audio: /dev/dsp, AudioEngine, and an AC'97 under it
A program that wants to make a sound opens /dev/dsp, writes PCM, and closes
it. That is what UNIX audio has always been and it now exists here:
tone 440 2
Three pieces, in the order a sample passes through them. **/dev/dsp** is a
character device where write() is audio and a handful of OSS ioctls say what
the samples are. **AudioEngine** is everything above a driver that is not
specific to a chip -- the format, whether there is room, and what a write does
when there is not. **A driver** is bound by class, exactly as a display driver
is: device_find_class(DEVCLASS_AUDIO).
OSS numbering rather than something new, because every UNIX audio program ever
written already knows it and the only thing a different set would achieve is
making ports harder. They are read/write ioctls, which is the part that
matters: a program asks for 44100, the device sets 48000 and writes 48000
back, the program resamples. One that ignores the answer plays 9% fast, and
that is its bug rather than the driver's.
**The engine is deliberately one stream.** Mixing several programs is a real
feature with a real design behind it, and building it before anything had
played a single sound would be exactly what docs/plan/1.0.md keeps a register
for: work that exists and is connected to nothing. The second program that
wants to play at the same time is what should cause it to be written.
**audio_wait() sleeps on the timer tick, not on the device.** That looks like
the lazy choice and is not: a ring that drains is a ring with room, so asking
again in ten milliseconds always makes progress, whereas sleeping on the card
makes audio depend on an interrupt arriving. On a machine whose line is
misrouted that is not a stutter, it is a writer that never wakes. The handler
still accounts for finished buffers -- deleting it would cost efficiency, not
correctness -- and it retires descriptors through the same `tail` pointer
queue() uses, so the two cannot disagree about what is in flight.
**AC'97 first because HDA is two unproven things at once.** It is the simplest
audio device that exists on real machines and in QEMU both. Intel HDA is what
the laptop actually has and is a much larger driver; writing it against an
interface nothing had ever played through would have meant debugging the
driver and the interface simultaneously. HDA arrives as a second
struct audio_ops and nothing above it changes -- which is the entire point of
the class.
Two things the wiring needed: PCI class 0x04 now maps to DEVCLASS_AUDIO (the
driver bound and /proc/devices showed it, but audio_get() found nothing,
because the class byte had never been translated), and include/x86.h grew
inw() -- AC'97's mixer is all 16-bit registers and reading one a byte at a
time returns the low half twice on some codecs.
**Tested by measuring what came out, not by not crashing.** QEMU's wav backend
writes the guest's audio to a file; `tone 440 2` produced 1.97 seconds of
44.1 kHz stereo with peak amplitude 14177 against the generator's table
maximum of 14178, and 880 zero crossings per second -- 440 Hz exactly. wav is
on every QEMU target rather than a host backend, because a build machine may
have no sound card and it is the only backend whose output can be checked.
Both supported configurations: one boot each, no traps, no panics, socktest
and memfdtest green.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
Nexoniarz
parent
3eb2e97f7b
commit
9fea18b18b
18 changed files with 1110 additions and 5 deletions
21
Makefile
21
Makefile
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@ -26,7 +26,7 @@ KERN_CORE = $(addprefix $(BUILD)/kernel/core/, \
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KERN_DEV = $(addprefix $(BUILD)/kernel/dev/, \
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KERN_DEV = $(addprefix $(BUILD)/kernel/dev/, \
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bio.o cdev.o device.o disk.o fb.o ide.o input.o irq.o kbd.o keymap.o mouse.o \
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bio.o cdev.o device.o disk.o fb.o ide.o input.o irq.o kbd.o keymap.o mouse.o \
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pci.o pciuser.o text.o ttf.o uart.o gfx.o vt.o ramdisk.o procfs.o \
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pci.o pciuser.o text.o ttf.o uart.o gfx.o vt.o ramdisk.o procfs.o \
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dbg.o netuser.o)
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dbg.o netuser.o audio.o)
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# Drivers for hardware that has to be *found* rather than assumed. Anything
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# Drivers for hardware that has to be *found* rather than assumed. Anything
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# discovered by walking a bus belongs here; the fixed-address legacy devices
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# discovered by walking a bus belongs here; the fixed-address legacy devices
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@ -43,6 +43,7 @@ KERN_DRIVERS += $(BUILD)/kernel/drivers/gpu/vga/vga_pci.o
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KERN_DRIVERS += $(BUILD)/kernel/drivers/gpu/vga/vga_fb.o
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KERN_DRIVERS += $(BUILD)/kernel/drivers/gpu/vga/vga_fb.o
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KERN_DRIVERS += $(BUILD)/kernel/drivers/gpu/virtio_gpu/virtio_gpu.o
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KERN_DRIVERS += $(BUILD)/kernel/drivers/gpu/virtio_gpu/virtio_gpu.o
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KERN_DRIVERS += $(BUILD)/kernel/drivers/net/e1000/e1000.o
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KERN_DRIVERS += $(BUILD)/kernel/drivers/net/e1000/e1000.o
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KERN_DRIVERS += $(BUILD)/kernel/drivers/audio/ac97.o
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KERN_DRIVERS += $(BUILD)/kernel/drivers/bus/xhci/xhci.o
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KERN_DRIVERS += $(BUILD)/kernel/drivers/bus/xhci/xhci.o
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KERN_DRIVERS += $(BUILD)/kernel/drivers/usb/core/usb.o
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KERN_DRIVERS += $(BUILD)/kernel/drivers/usb/core/usb.o
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KERN_DRIVERS += $(BUILD)/kernel/drivers/usb/hid/usb_hid.o
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KERN_DRIVERS += $(BUILD)/kernel/drivers/usb/hid/usb_hid.o
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@ -108,7 +109,7 @@ KERN_NOENTRY = $(filter-out $(BUILD)/kernel/arch/x86_64/entry.o, $(KERNOBJS))
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# Third-party software does NOT go here — see ports/.
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# Third-party software does NOT go here — see ports/.
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# -----------------------------------------------------------------------
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# -----------------------------------------------------------------------
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ULIB = $(addprefix $(BUILD)/lib/, start.o glue.o usys.o)
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ULIB = $(addprefix $(BUILD)/lib/, start.o glue.o usys.o)
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CMDS = schinit schinitd fbinfo shmtest socktest inputtest nettest reflink schattr ping chvt loadkeys sigtest memfdtest pcitest vgpud schdbg schdbgd resolvconf httpd schmode netecho ldlsd
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CMDS = schinit schinitd fbinfo shmtest socktest inputtest nettest reflink schattr ping chvt loadkeys sigtest memfdtest pcitest vgpud schdbg schdbgd resolvconf httpd schmode netecho ldlsd tone
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CMDBINS = $(addprefix $(BUILD)/cmd/, $(CMDS))
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CMDBINS = $(addprefix $(BUILD)/cmd/, $(CMDS))
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# -----------------------------------------------------------------------
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# -----------------------------------------------------------------------
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@ -194,6 +195,18 @@ QEMU_DISPLAY = -vga std -device virtio-gpu-pci
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# claim and exits, and the single window is the thing you wanted to look at.
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# claim and exits, and the single window is the thing you wanted to look at.
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QEMU_DISPLAY_1 = -vga std
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QEMU_DISPLAY_1 = -vga std
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# Sound, on every QEMU target.
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#
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# `wav` rather than a host audio backend: a build machine may have no
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# soundcard, no PulseAudio and no session bus, and a QEMU that fails to open
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# one of those prints a warning per voice and carries on -- which is noise in
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# every boot log for a feature most runs are not testing. Writing to a file
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# works everywhere and is the only backend that can be *checked*: the audio
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# test plays a tone and measures the zero crossings of what came out.
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#
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# To actually hear it: make qemu QEMU_AUDIO='-audiodev pa,id=snd0 -device AC97,audiodev=snd0'
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QEMU_AUDIO ?= -audiodev wav,id=snd0,path=$(BUILD)/qemu-audio.wav -device AC97,audiodev=snd0
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# A network card, on every QEMU target.
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# A network card, on every QEMU target.
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#
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#
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# Spelled out rather than left to QEMU's default NIC. The default exists and is
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# Spelled out rather than left to QEMU's default NIC. The default exists and is
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@ -643,7 +656,7 @@ ovmf: $(OVMF_CODE) $(OVMF_VARS)
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all: $(OVMF_CODE) $(OVMF_VARS)
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all: $(OVMF_CODE) $(OVMF_VARS)
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qemu-uefi: esp $(BUILD)/schfs.img $(OVMF_CODE) $(OVMF_VARS)
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qemu-uefi: esp $(BUILD)/schfs.img $(OVMF_CODE) $(OVMF_VARS)
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$(QEMU) -machine pc-i440fx-9.2 -drive if=pflash,format=raw,unit=0,readonly=on,file=$(OVMF_CODE) -drive if=pflash,format=raw,unit=1,file=$(OVMF_VARS) -drive file=fat:rw:$(BUILD)/esp,index=0,media=disk,format=raw -drive file=$(BUILD)/schfs.img,format=raw,index=1,media=disk -m 1G -smp 1 $(QEMU_ACCEL) -serial mon:stdio $(QEMU_DISPLAY) $(QEMU_INPUT) $(QEMU_NET)
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$(QEMU) -machine pc-i440fx-9.2 -drive if=pflash,format=raw,unit=0,readonly=on,file=$(OVMF_CODE) -drive if=pflash,format=raw,unit=1,file=$(OVMF_VARS) -drive file=fat:rw:$(BUILD)/esp,index=0,media=disk,format=raw -drive file=$(BUILD)/schfs.img,format=raw,index=1,media=disk -m 1G -smp 1 $(QEMU_ACCEL) -serial mon:stdio $(QEMU_DISPLAY) $(QEMU_INPUT) $(QEMU_NET) $(QEMU_AUDIO)
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# Build the ramdisk-root variant. This is a target rather than just
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# Build the ramdisk-root variant. This is a target rather than just
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# "make RAMROOT=1" because toggling RAMROOT changes CFLAGS (-DRAMDISK_ROOT),
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# "make RAMROOT=1" because toggling RAMROOT changes CFLAGS (-DRAMDISK_ROOT),
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@ -1356,7 +1369,7 @@ qemu-gdb: esp $(BUILD)/schfs.img $(OVMF_CODE) $(OVMF_VARS)
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-S -gdb tcp::$(GDBPORT)
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-S -gdb tcp::$(GDBPORT)
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qemu-kvm: esp $(BUILD)/schfs.img $(OVMF_CODE) $(OVMF_VARS)
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qemu-kvm: esp $(BUILD)/schfs.img $(OVMF_CODE) $(OVMF_VARS)
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$(QEMU) -enable-kvm -serial mon:stdio $(QEMU_DISPLAY) $(QEMU_INPUT) $(QEMU_NET) -cpu host \
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$(QEMU) -enable-kvm -serial mon:stdio $(QEMU_DISPLAY) $(QEMU_INPUT) $(QEMU_NET) $(QEMU_AUDIO) -cpu host \
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$(OVMF_DRIVES) -m 1G -smp $(SMP) -machine pc-i440fx-9.2
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$(OVMF_DRIVES) -m 1G -smp $(SMP) -machine pc-i440fx-9.2
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qemu: esp $(BUILD)/schfs.img $(OVMF_CODE) $(OVMF_VARS)
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qemu: esp $(BUILD)/schfs.img $(OVMF_CODE) $(OVMF_VARS)
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134
cmd/tone/main.c
Normal file
134
cmd/tone/main.c
Normal file
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@ -0,0 +1,134 @@
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// tone -- write a sine wave to /dev/dsp.
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//
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// The smallest program that proves the audio path end to end: it asks the
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// device what it can play, generates that, and writes it. If a machine makes
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// this noise, every layer between a write() and a speaker is working.
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//
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// tone 440 Hz for one second
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// tone 1000 1000 Hz for one second
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// tone 1000 3 1000 Hz for three seconds
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//
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// Deliberately not a WAV player. A player has to parse a header, and a header
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// is a second thing to get wrong while testing the first.
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#include "types.h"
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#include "user.h"
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#include "fcntl.h"
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#include "audio.h"
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// A quarter-amplitude sine, from a table rather than a libm that does not
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// exist here. 64 points is audibly a sine and arithmetically exact.
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static const short SINE[64] = {
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0, 803, 1605, 2404, 3196, 3980, 4753, 5511,
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6254, 6977, 7679, 8357, 9008, 9630, 10220, 10777,
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11297, 11780, 12222, 12623, 12980, 13293, 13559, 13778,
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13951, 14075, 14151, 14178, 14156, 14085, 13965, 13797,
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13581, 13318, 13009, 12655, 12257, 11818, 11338, 10820,
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10266, 9679, 9060, 8413, 7740, 7044, 6329, 5597,
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4851, 4096, 3334, 2569, 1804, 1043, 289, -453,
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-1180, -1889, -2576, -3239, -3874, -4479, -5051, -5588
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};
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// lib/ has no stdio: write(2) is the whole of it, which is why every
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// first-party program in cmd/ carries these three lines.
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static void
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say(const char *s)
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{
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int n = 0;
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while (s[n]) n++;
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write(1, (void *)s, n);
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}
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static void
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sayn(int v)
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{
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char b[12];
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int i = 0, j;
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if (v == 0) { say("0"); return; }
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if (v < 0) { say("-"); v = -v; }
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while (v && i < 11) { b[i++] = (char)('0' + v % 10); v /= 10; }
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for (j = i; j-- > 0; )
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write(1, &b[j], 1);
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}
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static int
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num(const char *s)
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{
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int v = 0;
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while (*s >= '0' && *s <= '9')
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v = v * 10 + (*s++ - '0');
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return v;
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}
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int
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main(int argc, char *argv[])
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{
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int hz = argc > 1 ? num(argv[1]) : 440;
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int secs = argc > 2 ? num(argv[2]) : 1;
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int rate = 48000, channels = 2, fmt = AFMT_S16_LE;
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short buf[1024]; /* 512 stereo frames */
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int fd, phase = 0;
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if (hz < 20 || hz > 20000) {
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say("tone: "); sayn(hz); say(" Hz is not audible\n");
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return 1;
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}
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if (secs < 1 || secs > 30)
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secs = 1;
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fd = open("/dev/dsp", O_WRONLY);
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if (fd < 0) {
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say("tone: no /dev/dsp -- is there an audio device?\n");
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return 1;
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}
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// Ask, then believe the answer. These are read/write on purpose: the
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// device writes back what it actually set, and a program that ignores
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// that plays at the wrong speed and blames the driver.
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if (ioctl(fd, SNDCTL_DSP_SETFMT, &fmt) < 0 || fmt != AFMT_S16_LE) {
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say("tone: the device will not take 16-bit samples\n");
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return 1;
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}
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ioctl(fd, SNDCTL_DSP_CHANNELS, &channels);
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ioctl(fd, SNDCTL_DSP_SPEED, &rate);
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say("tone: "); sayn(hz); say(" Hz for "); sayn(secs);
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say(" s at "); sayn(rate); say(" Hz, "); sayn(channels);
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say(" channel(s)\n");
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// The phase step in 1/256ths of a table entry, so a 440 Hz tone at 48 kHz
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// is not quantised into something a tuner would argue with.
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int step = (hz * 64 * 256) / rate;
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int frames_total = rate * secs;
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while (frames_total > 0) {
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int frames = frames_total > 512 ? 512 : frames_total;
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int i;
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for (i = 0; i < frames; i++) {
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short s = SINE[(phase >> 8) & 63];
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phase += step;
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if (channels == 2) {
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buf[i * 2] = s;
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buf[i * 2 + 1] = s;
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} else {
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buf[i] = s;
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}
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}
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int bytes = frames * channels * 2;
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if (write(fd, buf, bytes) != bytes) {
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say("tone: short write -- the device stopped taking audio\n");
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close(fd);
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return 1;
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}
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frames_total -= frames;
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}
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// Wait for it to finish rather than exiting on top of it. close() drains
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// too, but saying so is the point of the ioctl existing.
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ioctl(fd, SNDCTL_DSP_SYNC, 0);
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close(fd);
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return 0;
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}
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@ -92,6 +92,7 @@ Read in this order if you are new:
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| [graphics.md](graphics.md) | Framebuffer, text rendering, the console, and PSOGM. |
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| [graphics.md](graphics.md) | Framebuffer, text rendering, the console, and PSOGM. |
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| [terminals.md](terminals.md) | The six virtual terminals, and the chord that switches them. |
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| [terminals.md](terminals.md) | The six virtual terminals, and the chord that switches them. |
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| [networking.md](networking.md) | NIC drivers, lwIP, and both socket families. |
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| [networking.md](networking.md) | NIC drivers, lwIP, and both socket families. |
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| [audio.md](audio.md) | `/dev/dsp`, AudioEngine, and the AC'97 driver under it. |
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| [init.md](init.md) | `schinit`, PID 1 as a role, and the job manifests. |
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| [init.md](init.md) | `schinit`, PID 1 as a role, and the job manifests. |
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| [debugging.md](debugging.md) | Symbols, a log that outlives the kernel, and asking the kernel a question. |
|
| [debugging.md](debugging.md) | Symbols, a log that outlives the kernel, and asking the kernel a question. |
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| [ldls.md](ldls.md) | Running somebody else's drivers: a Linux `.ko`, in a process, reaching hardware through `/dev/pci`. |
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| [ldls.md](ldls.md) | Running somebody else's drivers: a Linux `.ko`, in a process, reaching hardware through `/dev/pci`. |
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124
docs/architecture/audio.md
Normal file
124
docs/architecture/audio.md
Normal file
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@ -0,0 +1,124 @@
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<!-- SPDX-License-Identifier: Apache-2.0 -->
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# Audio
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A program that wants to make a sound opens `/dev/dsp`, writes PCM to it, and
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closes it. That is what UNIX audio has always been, and it is what this is.
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```sh
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tone 440 2 # 440 Hz for two seconds
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```
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Three pieces, in the order a sample passes through them:
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| | |
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| --- | --- |
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| **`/dev/dsp`** | `kernel/dev/audio.c`. A character device: `write()` is audio, and a handful of OSS ioctls say what the samples are. |
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|
| **AudioEngine** | The same file. Everything above a driver that is not specific to a chip: the format, whether there is room, and what a write does when there is not. |
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| **a driver** | `kernel/drivers/audio/ac97.c` today. Bound by class, exactly as a display driver is — `device_find_class(DEVCLASS_AUDIO)`. |
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## Why OSS and not something new
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The ioctls are `SNDCTL_DSP_SPEED`, `SNDCTL_DSP_CHANNELS`, `SNDCTL_DSP_SETFMT`,
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`SNDCTL_DSP_SYNC` and `SNDCTL_DSP_GETOSPACE`, with OSS's own numbering. They
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are not invented here and they are not copied for nostalgia: every UNIX audio
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program that has ever been written knows them, and the only thing a different
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||||||
|
set would achieve is making ports harder.
|
||||||
|
|
||||||
|
They are **read/write** ioctls, which is the part that matters. A program asks
|
||||||
|
for 44100; the device sets 48000 and writes 48000 back; the program resamples.
|
||||||
|
One that ignores the answer plays everything 9% fast, and that is its bug
|
||||||
|
rather than the driver's. `configure` in the class works the same way, and for
|
||||||
|
the same reason — a driver that can only do 48 kHz says so *there*, rather than
|
||||||
|
by quietly failing a `write()` later.
|
||||||
|
|
||||||
|
## What the engine is, and what it deliberately is not
|
||||||
|
|
||||||
|
It owns format negotiation, the "is there room" question, and blocking. Those
|
||||||
|
are genuinely shared: a second driver should not have to re-implement *wait
|
||||||
|
until the speaker has caught up*.
|
||||||
|
|
||||||
|
**It is one stream.** Mixing several programs into one device is a real feature
|
||||||
|
with a real design behind it, and building it before anything had played a
|
||||||
|
single sound would be exactly the mistake [../plan/1.0.md](../plan/1.0.md)
|
||||||
|
keeps a register for: work that exists and is connected to nothing. The second
|
||||||
|
program that wants to play at the same time is what should cause it to be
|
||||||
|
written.
|
||||||
|
|
||||||
|
### Waiting on the tick, not on the device
|
||||||
|
|
||||||
|
`audio_wait()` sleeps until the next timer tick rather than on an interrupt
|
||||||
|
from the sound card, which looks like the lazy choice and is not.
|
||||||
|
|
||||||
|
A ring that drains is a ring with room in it, so asking again in ten
|
||||||
|
milliseconds always makes progress. Sleeping on the *device* would make audio
|
||||||
|
depend on the interrupt arriving — and on a machine whose line is misrouted,
|
||||||
|
or a chip that needs a kick, that is not a stutter, it is a writer that never
|
||||||
|
wakes up. The interrupt handler is still there and still accounts for finished
|
||||||
|
buffers; the point is that deleting it would cost efficiency and not
|
||||||
|
correctness.
|
||||||
|
|
||||||
|
## AC'97 first, and HDA later
|
||||||
|
|
||||||
|
AC'97 is the simplest audio device that exists both on real machines and in
|
||||||
|
QEMU. Intel HDA is what a laptop built this century actually has, and it is a
|
||||||
|
much larger driver — codec enumeration, CORB/RIRB, stream descriptors. Writing
|
||||||
|
it first would have meant writing two unproven things at once: a driver, and
|
||||||
|
the interface it is the only user of.
|
||||||
|
|
||||||
|
The class is the whole point of the order. HDA arrives as a second
|
||||||
|
`struct audio_ops` and nothing above it changes.
|
||||||
|
|
||||||
|
### How it plays
|
||||||
|
|
||||||
|
The chip reads a *buffer descriptor list*: 32 entries, each naming a physical
|
||||||
|
address and a length. It plays the entry at `CIV` and stops when it reaches
|
||||||
|
`LVI`, the last valid index. Playing continuously is therefore not "start it
|
||||||
|
and walk away" — it is keeping `LVI` ahead of `CIV`, which is what `queue()`
|
||||||
|
does, one 4 KB descriptor at a time.
|
||||||
|
|
||||||
|
Retiring finished descriptors happens in **both** `queue()` and the interrupt
|
||||||
|
handler, through the same `tail` pointer so the two cannot disagree. That is
|
||||||
|
the same "the interrupt is an optimisation" stance as above.
|
||||||
|
|
||||||
|
Both register files are **I/O ports**, not MMIO — which is why nothing in the
|
||||||
|
driver maps anything. `bar[n].is_io` is what says so, and a driver that
|
||||||
|
`ioremap`ed these would be mapping a port number as though it were an address.
|
||||||
|
|
||||||
|
## How it is tested
|
||||||
|
|
||||||
|
QEMU's `wav` audio backend writes what the guest plays to a file, so the test
|
||||||
|
is not "it did not crash":
|
||||||
|
|
||||||
|
```sh
|
||||||
|
make qemu # QEMU_AUDIO puts an AC97 on every target
|
||||||
|
tone 440 2
|
||||||
|
```
|
||||||
|
|
||||||
|
and the file is measured — 1.97 seconds of 44.1 kHz stereo, peak amplitude
|
||||||
|
14177 against the tone generator's table maximum of 14178, and 880 zero
|
||||||
|
crossings per second, which is 440 Hz exactly.
|
||||||
|
|
||||||
|
`wav` rather than a host backend on purpose: a build machine may have no sound
|
||||||
|
card, no PulseAudio and no session bus, and it is the only backend whose output
|
||||||
|
can be *checked*. To actually hear it:
|
||||||
|
|
||||||
|
```sh
|
||||||
|
make qemu QEMU_AUDIO='-audiodev pa,id=snd0 -device AC97,audiodev=snd0'
|
||||||
|
```
|
||||||
|
|
||||||
|
## What it does not do
|
||||||
|
|
||||||
|
- **Recording.** `read()` on `/dev/dsp` returns `ENOSYS` rather than zero,
|
||||||
|
because zero is end-of-file and a recorder would write an empty file and
|
||||||
|
call it a success.
|
||||||
|
- **Mixing.** One stream; see above.
|
||||||
|
- **Mono.** The driver reports two channels because AC'97 plays stereo, and a
|
||||||
|
mono stream would have to be doubled somewhere. The write-back tells the
|
||||||
|
caller, which is the whole reason the ioctl has a direction.
|
||||||
|
- **Formats other than signed 16-bit little-endian.** It is what every PC
|
||||||
|
audio chip takes natively and what a WAV file already contains. Converting
|
||||||
|
in the kernel to satisfy a caller that could have converted first is not an
|
||||||
|
obvious trade.
|
||||||
|
- **Volume.** The mixer is set to full and left there. How loud a machine is is
|
||||||
|
not the kernel's decision, and a device that comes up silent reads as broken
|
||||||
|
to whoever is testing it.
|
||||||
103
include/audio.h
Normal file
103
include/audio.h
Normal file
|
|
@ -0,0 +1,103 @@
|
||||||
|
#pragma once
|
||||||
|
|
||||||
|
// The audio class, and the engine above it.
|
||||||
|
//
|
||||||
|
// A program that wants to make a sound should be able to open a device, write
|
||||||
|
// samples to it, and stop -- which is what UNIX audio has always been, and
|
||||||
|
// what this is. `/dev/dsp`, PCM in, `write()`, and a handful of ioctls to say
|
||||||
|
// what the samples are. No server, no session bus, no protocol.
|
||||||
|
//
|
||||||
|
// The shape is the display class's, for the same reason: a consumer asks for
|
||||||
|
// "the audio device" and gets whatever is bound, so adding a second driver is
|
||||||
|
// not an edit to every caller. Found with device_find_class(DEVCLASS_AUDIO).
|
||||||
|
//
|
||||||
|
// ---------------------------------------------------------------------------
|
||||||
|
//
|
||||||
|
// **What the engine is for, and what it is not yet.**
|
||||||
|
//
|
||||||
|
// AudioEngine owns everything above a driver that is not specific to a chip:
|
||||||
|
// what format the stream is in, how many bytes the hardware can take, and what
|
||||||
|
// a write() does when it cannot take them all. That is genuinely shared -- a
|
||||||
|
// second driver should not re-implement "block until there is room".
|
||||||
|
//
|
||||||
|
// It is deliberately *one stream*. Mixing several programs into one device is
|
||||||
|
// a real feature with a real design behind it, and building it before anything
|
||||||
|
// plays a single sound would be the mistake docs/plan/1.0.md warns about: work
|
||||||
|
// that exists and is connected to nothing. The second program that wants to
|
||||||
|
// play at the same time is what should cause it to be written.
|
||||||
|
|
||||||
|
struct device;
|
||||||
|
|
||||||
|
// Interleaved signed 16-bit little-endian, which is what every PC audio chip
|
||||||
|
// takes natively and what a WAV file already contains. Others exist and none
|
||||||
|
// of them is needed to make a sound; converting in the kernel to satisfy a
|
||||||
|
// caller that could have converted first is not an obvious trade.
|
||||||
|
#define AUDIO_FMT_S16LE 16
|
||||||
|
|
||||||
|
struct audio_format {
|
||||||
|
unsigned int rate; // frames per second -- 48000, 44100
|
||||||
|
unsigned int channels; // 1 mono, 2 stereo
|
||||||
|
unsigned int bits; // AUDIO_FMT_S16LE
|
||||||
|
};
|
||||||
|
|
||||||
|
struct audio_ops {
|
||||||
|
// Take this format, or report what the hardware will do instead by writing
|
||||||
|
// back into `f` and returning 0. Returning negative means it cannot play at
|
||||||
|
// all. A driver that only does 48 kHz stereo says so here rather than
|
||||||
|
// failing a write() later, which is the difference between a program that
|
||||||
|
// adapts and a program that gets silence.
|
||||||
|
int (*configure)(struct device *, struct audio_format *f);
|
||||||
|
|
||||||
|
// Bytes that can be queued right now without waiting. The engine uses this
|
||||||
|
// to decide whether a write() has to block, so a driver that returns a
|
||||||
|
// hardware-accurate number is a driver whose write() latency is honest.
|
||||||
|
int (*space)(struct device *);
|
||||||
|
|
||||||
|
// Queue PCM. Returns bytes accepted, which may be fewer than offered and
|
||||||
|
// may be zero; the engine handles the remainder. Never blocks.
|
||||||
|
int (*queue)(struct device *, const void *pcm, int bytes);
|
||||||
|
|
||||||
|
// Start the stream if it is not running. Called by the engine once there is
|
||||||
|
// something to play, rather than at open: a device left running with an
|
||||||
|
// empty ring plays whatever was in it, which on real hardware is a loop of
|
||||||
|
// the last buffer and sounds exactly as bad as it reads.
|
||||||
|
void (*start)(struct device *);
|
||||||
|
|
||||||
|
// Stop, and discard anything queued.
|
||||||
|
void (*stop)(struct device *);
|
||||||
|
|
||||||
|
// Bytes still to be played. Zero means the hardware has finished. The
|
||||||
|
// engine polls this for SNDCTL_DSP_SYNC rather than a driver growing its
|
||||||
|
// own wait loop.
|
||||||
|
int (*pending)(struct device *);
|
||||||
|
};
|
||||||
|
|
||||||
|
// --- what the kernel uses --------------------------------------------------
|
||||||
|
|
||||||
|
struct device *audio_get(void);
|
||||||
|
int audio_configure(struct audio_format *f); // 0, or negative
|
||||||
|
int audio_write(const void *pcm, int bytes); // bytes queued, or negative
|
||||||
|
void audio_drain(void);
|
||||||
|
void audio_stop(void);
|
||||||
|
|
||||||
|
// --- what userspace uses ---------------------------------------------------
|
||||||
|
//
|
||||||
|
// OSS numbering, which is the one every UNIX audio program already knows and
|
||||||
|
// the only reason to invent a different set would be to make ports harder.
|
||||||
|
// These four are the whole interface a tone generator or a WAV player needs.
|
||||||
|
|
||||||
|
#define SNDCTL_DSP_SPEED 0xC0045002 // int in/out: sample rate
|
||||||
|
#define SNDCTL_DSP_CHANNELS 0xC0045006 // int in/out: 1 or 2
|
||||||
|
#define SNDCTL_DSP_SETFMT 0xC0045005 // int in/out: AFMT_S16_LE
|
||||||
|
#define SNDCTL_DSP_SYNC 0x00005001 // wait for the queue to drain
|
||||||
|
#define SNDCTL_DSP_GETOSPACE 0x8010500C // struct audio_buf_info out
|
||||||
|
#define SNDCTL_DSP_RESET 0x00005000 // stop, discard
|
||||||
|
|
||||||
|
#define AFMT_S16_LE 0x00000010
|
||||||
|
|
||||||
|
struct audio_buf_info {
|
||||||
|
int fragments; // how many whole fragments are free
|
||||||
|
int fragstotal; // how many there are in total
|
||||||
|
int fragsize; // bytes in one
|
||||||
|
int bytes; // free bytes, which is the number that matters
|
||||||
|
};
|
||||||
|
|
@ -611,6 +611,13 @@ void fbclose(struct inode*);
|
||||||
// further syscalls, so it is the last the kernel hears about it.
|
// further syscalls, so it is the last the kernel hears about it.
|
||||||
void fb_mapped(void);
|
void fb_mapped(void);
|
||||||
|
|
||||||
|
// AudioEngine and /dev/dsp. kernel/dev/audio.c, include/audio.h.
|
||||||
|
int dspread(struct inode*, uint64, char*, int);
|
||||||
|
int dspwrite(struct inode*, uint64, char*, int);
|
||||||
|
void dspclose(struct inode*);
|
||||||
|
int dsp_ioctl(int request, uint64 argp);
|
||||||
|
void audio_wait(struct device *);
|
||||||
|
|
||||||
// The crash screen, on displays other than the console's. kernel/dev/device.c.
|
// The crash screen, on displays other than the console's. kernel/dev/device.c.
|
||||||
void display_panic_present(void);
|
void display_panic_present(void);
|
||||||
// Push the console's newly-drawn rows to a second display, if the kernel
|
// Push the console's newly-drawn rows to a second display, if the kernel
|
||||||
|
|
|
||||||
|
|
@ -46,6 +46,7 @@ enum dev_class {
|
||||||
DEVCLASS_STORAGE,
|
DEVCLASS_STORAGE,
|
||||||
DEVCLASS_NET,
|
DEVCLASS_NET,
|
||||||
DEVCLASS_BUS, // a controller that finds more devices (xHCI, hubs)
|
DEVCLASS_BUS, // a controller that finds more devices (xHCI, hubs)
|
||||||
|
DEVCLASS_AUDIO,
|
||||||
DEVCLASS_NCLASS
|
DEVCLASS_NCLASS
|
||||||
};
|
};
|
||||||
|
|
||||||
|
|
|
||||||
|
|
@ -187,3 +187,5 @@ extern struct devsw devsw[];
|
||||||
#define CONSOLE 1
|
#define CONSOLE 1
|
||||||
// Major number of /dev/input/eventN. The minor is the device index.
|
// Major number of /dev/input/eventN. The minor is the device index.
|
||||||
#define INPUT_MAJOR 7
|
#define INPUT_MAJOR 7
|
||||||
|
// Major number of /dev/dsp. See include/audio.h.
|
||||||
|
#define AUDIO_MAJOR 12
|
||||||
|
|
|
||||||
|
|
@ -29,7 +29,7 @@
|
||||||
#define NOFILE 128 // open files per process
|
#define NOFILE 128 // open files per process
|
||||||
#define NFILE 512 // open files per system
|
#define NFILE 512 // open files per system
|
||||||
#define NINODE 200 // maximum number of active i-nodes
|
#define NINODE 200 // maximum number of active i-nodes
|
||||||
#define NDEV 12 // maximum major device number
|
#define NDEV 13 // maximum major device number
|
||||||
#define RAMDISK_DEV 2 // memory-backed block device (kernel/dev/ramdisk.c)
|
#define RAMDISK_DEV 2 // memory-backed block device (kernel/dev/ramdisk.c)
|
||||||
#define USBDISK_DEV 3 // USB mass storage (kernel/drivers/usb_storage.c)
|
#define USBDISK_DEV 3 // USB mass storage (kernel/drivers/usb_storage.c)
|
||||||
|
|
||||||
|
|
|
||||||
|
|
@ -40,6 +40,17 @@ outb(ushort port, uchar data)
|
||||||
asm volatile("out %0,%1" : : "a" (data), "d" (port));
|
asm volatile("out %0,%1" : : "a" (data), "d" (port));
|
||||||
}
|
}
|
||||||
|
|
||||||
|
// 16 bits. Added for AC'97, whose mixer is entirely 16-bit registers: reading
|
||||||
|
// one of them a byte at a time returns the low half twice on some codecs,
|
||||||
|
// because the read of the low byte is what latches the pair.
|
||||||
|
static inline ushort
|
||||||
|
inw(ushort port)
|
||||||
|
{
|
||||||
|
ushort data;
|
||||||
|
asm volatile("inw %1,%0" : "=a" (data) : "d" (port));
|
||||||
|
return data;
|
||||||
|
}
|
||||||
|
|
||||||
static inline uint
|
static inline uint
|
||||||
inl(ushort port)
|
inl(ushort port)
|
||||||
{
|
{
|
||||||
|
|
|
||||||
284
kernel/dev/audio.c
Normal file
284
kernel/dev/audio.c
Normal file
|
|
@ -0,0 +1,284 @@
|
||||||
|
// AudioEngine: the audio class, and /dev/dsp above it.
|
||||||
|
//
|
||||||
|
// See include/audio.h for what this is and what it deliberately is not. In
|
||||||
|
// short: a program opens /dev/dsp, says what its samples are, writes them, and
|
||||||
|
// stops. Everything here is either the class vtable's thin wrapper or the part
|
||||||
|
// of "play this" that is not specific to a chip.
|
||||||
|
|
||||||
|
#include "types.h"
|
||||||
|
#include "defs.h"
|
||||||
|
#include "param.h"
|
||||||
|
#include "spinlock.h"
|
||||||
|
#include "sleeplock.h"
|
||||||
|
#include "fs.h"
|
||||||
|
#include "file.h"
|
||||||
|
#include "device.h"
|
||||||
|
#include "audio.h"
|
||||||
|
#include "proc.h"
|
||||||
|
#include "uaccess.h"
|
||||||
|
#include "errno.h"
|
||||||
|
|
||||||
|
static struct spinlock audio_lock;
|
||||||
|
static int audio_lock_init;
|
||||||
|
|
||||||
|
// The format the device is currently in. Kept here rather than asked of the
|
||||||
|
// driver on every write, because a caller that set 44100 and got 48000 needs
|
||||||
|
// to be told once and then have it stay told.
|
||||||
|
static struct audio_format current_fmt = { 48000, 2, AUDIO_FMT_S16LE };
|
||||||
|
|
||||||
|
static void
|
||||||
|
lock_once(void)
|
||||||
|
{
|
||||||
|
if (!audio_lock_init) {
|
||||||
|
initlock(&audio_lock, "audio");
|
||||||
|
audio_lock_init = 1;
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
// --- the class -------------------------------------------------------------
|
||||||
|
|
||||||
|
struct device *
|
||||||
|
audio_get(void)
|
||||||
|
{
|
||||||
|
return device_find_class(DEVCLASS_AUDIO);
|
||||||
|
}
|
||||||
|
|
||||||
|
static const struct audio_ops *
|
||||||
|
ops_of(struct device *d)
|
||||||
|
{
|
||||||
|
return d && d->ops ? (const struct audio_ops *)d->ops : 0;
|
||||||
|
}
|
||||||
|
|
||||||
|
int
|
||||||
|
audio_configure(struct audio_format *f)
|
||||||
|
{
|
||||||
|
struct device *d = audio_get();
|
||||||
|
const struct audio_ops *o = ops_of(d);
|
||||||
|
int r;
|
||||||
|
|
||||||
|
if (!o || !o->configure)
|
||||||
|
return -ENODEV;
|
||||||
|
if (f->bits != AUDIO_FMT_S16LE)
|
||||||
|
return -EINVAL;
|
||||||
|
if (f->channels != 1 && f->channels != 2)
|
||||||
|
return -EINVAL;
|
||||||
|
if (f->rate < 4000 || f->rate > 192000)
|
||||||
|
return -EINVAL;
|
||||||
|
|
||||||
|
r = o->configure(d, f);
|
||||||
|
if (r < 0)
|
||||||
|
return r;
|
||||||
|
|
||||||
|
lock_once();
|
||||||
|
acquire(&audio_lock);
|
||||||
|
current_fmt = *f; // what the driver settled on, not what was asked
|
||||||
|
release(&audio_lock);
|
||||||
|
return 0;
|
||||||
|
}
|
||||||
|
|
||||||
|
// Queue bytes, blocking while the hardware is full.
|
||||||
|
//
|
||||||
|
// The blocking is here rather than in a driver because it is the same in every
|
||||||
|
// driver: there is a ring, it has room or it does not, and a writer that is
|
||||||
|
// ahead of the speaker has nothing useful to do but wait. Sleeping on the
|
||||||
|
// device and being woken by its interrupt is the whole of it.
|
||||||
|
int
|
||||||
|
audio_write(const void *pcm, int bytes)
|
||||||
|
{
|
||||||
|
struct device *d = audio_get();
|
||||||
|
const struct audio_ops *o = ops_of(d);
|
||||||
|
const char *p = pcm;
|
||||||
|
int done = 0;
|
||||||
|
|
||||||
|
if (!o || !o->queue)
|
||||||
|
return -ENODEV;
|
||||||
|
if (bytes <= 0)
|
||||||
|
return 0;
|
||||||
|
|
||||||
|
while (done < bytes) {
|
||||||
|
int n = o->queue(d, p + done, bytes - done);
|
||||||
|
|
||||||
|
if (n < 0)
|
||||||
|
return done ? done : n;
|
||||||
|
|
||||||
|
if (n == 0) {
|
||||||
|
// Full. Start what is already queued -- a writer that fills the ring
|
||||||
|
// and then waits for space would otherwise wait for a stream nobody
|
||||||
|
// started -- and give the CPU up until some of it has been played.
|
||||||
|
if (o->start)
|
||||||
|
o->start(d);
|
||||||
|
if (myproc() && myproc()->killed)
|
||||||
|
return done ? done : -EINTR;
|
||||||
|
audio_wait(d);
|
||||||
|
continue;
|
||||||
|
}
|
||||||
|
|
||||||
|
done += n;
|
||||||
|
}
|
||||||
|
|
||||||
|
if (o->start)
|
||||||
|
o->start(d);
|
||||||
|
return done;
|
||||||
|
}
|
||||||
|
|
||||||
|
// Wait for the hardware to make room. A driver signals this from its
|
||||||
|
// interrupt handler with audio_wakeup().
|
||||||
|
//
|
||||||
|
// The timeout is not a nicety: a driver whose interrupt never arrives -- a
|
||||||
|
// misrouted line, a chip that needs a kick -- would otherwise hang the writer
|
||||||
|
// for ever with no way to tell what happened. Waking up anyway and asking the
|
||||||
|
// hardware again turns that into audio that stutters, which is a bug report
|
||||||
|
// somebody can make.
|
||||||
|
void
|
||||||
|
audio_wait(struct device *d)
|
||||||
|
{
|
||||||
|
uint t0;
|
||||||
|
|
||||||
|
(void)d;
|
||||||
|
// One timer tick, the same way kernel/sys/sys_poll.c waits: there is no
|
||||||
|
// timed sleep() in this kernel, and adding one for a single caller would be
|
||||||
|
// a scheduler change to avoid a ten-line loop.
|
||||||
|
//
|
||||||
|
// Sleeping on `ticks` rather than on the device means a driver interrupt is
|
||||||
|
// not strictly required to make progress -- which is the point. A ring that
|
||||||
|
// drains is a ring that has room, and asking again in ten milliseconds
|
||||||
|
// costs one wakeup per buffer.
|
||||||
|
acquire(&tickslock);
|
||||||
|
t0 = ticks;
|
||||||
|
while (ticks == t0 && !(myproc() && myproc()->killed))
|
||||||
|
sleep(&ticks, &tickslock);
|
||||||
|
release(&tickslock);
|
||||||
|
}
|
||||||
|
|
||||||
|
void
|
||||||
|
audio_drain(void)
|
||||||
|
{
|
||||||
|
struct device *d = audio_get();
|
||||||
|
const struct audio_ops *o = ops_of(d);
|
||||||
|
int spins;
|
||||||
|
|
||||||
|
if (!o || !o->pending)
|
||||||
|
return;
|
||||||
|
|
||||||
|
// Bounded, for the same reason the wait above is. Ten seconds of audio is
|
||||||
|
// longer than any buffer this engine will hold, so a `pending` that has not
|
||||||
|
// reached zero by then is a driver that is not playing rather than one that
|
||||||
|
// is busy.
|
||||||
|
for (spins = 0; spins < 1000 && o->pending(d) > 0; spins++) {
|
||||||
|
if (myproc() && myproc()->killed)
|
||||||
|
return;
|
||||||
|
audio_wait(d);
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
void
|
||||||
|
audio_stop(void)
|
||||||
|
{
|
||||||
|
struct device *d = audio_get();
|
||||||
|
const struct audio_ops *o = ops_of(d);
|
||||||
|
|
||||||
|
if (o && o->stop)
|
||||||
|
o->stop(d);
|
||||||
|
}
|
||||||
|
|
||||||
|
// --- /dev/dsp ---------------------------------------------------------------
|
||||||
|
|
||||||
|
int
|
||||||
|
dspwrite(struct inode *ip, uint64 off, char *src, int n)
|
||||||
|
{
|
||||||
|
(void)ip; (void)off;
|
||||||
|
return audio_write(src, n);
|
||||||
|
}
|
||||||
|
|
||||||
|
// Recording is not implemented, and says so. Returning zero would look like
|
||||||
|
// end-of-file and a recorder would write an empty file and call it a success.
|
||||||
|
int
|
||||||
|
dspread(struct inode *ip, uint64 off, char *dst, int n)
|
||||||
|
{
|
||||||
|
(void)ip; (void)off; (void)dst; (void)n;
|
||||||
|
return -ENOSYS;
|
||||||
|
}
|
||||||
|
|
||||||
|
// The last descriptor is closing. Anything still queued is played out first:
|
||||||
|
// a program that writes a sound and exits expects to hear the end of it, and
|
||||||
|
// dropping the tail is the one behaviour that would make this device feel
|
||||||
|
// broken while technically working.
|
||||||
|
void
|
||||||
|
dspclose(struct inode *ip)
|
||||||
|
{
|
||||||
|
(void)ip;
|
||||||
|
audio_drain();
|
||||||
|
audio_stop();
|
||||||
|
}
|
||||||
|
|
||||||
|
int
|
||||||
|
dsp_ioctl(int request, uint64 argp)
|
||||||
|
{
|
||||||
|
struct device *d = audio_get();
|
||||||
|
const struct audio_ops *o = ops_of(d);
|
||||||
|
struct audio_format f;
|
||||||
|
int val;
|
||||||
|
|
||||||
|
if (!o)
|
||||||
|
return -ENODEV;
|
||||||
|
|
||||||
|
lock_once();
|
||||||
|
acquire(&audio_lock);
|
||||||
|
f = current_fmt;
|
||||||
|
release(&audio_lock);
|
||||||
|
|
||||||
|
switch (request) {
|
||||||
|
case SNDCTL_DSP_SPEED:
|
||||||
|
case SNDCTL_DSP_CHANNELS:
|
||||||
|
case SNDCTL_DSP_SETFMT: {
|
||||||
|
if (copy_from_user(&val, argp, sizeof(val)) < 0)
|
||||||
|
return -EFAULT;
|
||||||
|
|
||||||
|
if (request == SNDCTL_DSP_SPEED) f.rate = (unsigned)val;
|
||||||
|
else if (request == SNDCTL_DSP_CHANNELS) f.channels = (unsigned)val;
|
||||||
|
else {
|
||||||
|
if (val != AFMT_S16_LE)
|
||||||
|
return -EINVAL;
|
||||||
|
f.bits = AUDIO_FMT_S16LE;
|
||||||
|
}
|
||||||
|
|
||||||
|
int r = audio_configure(&f);
|
||||||
|
if (r < 0)
|
||||||
|
return r;
|
||||||
|
|
||||||
|
// OSS writes back what was actually set, which is the entire reason these
|
||||||
|
// are read/write ioctls: a program asks for 44100, is told 48000, and
|
||||||
|
// resamples. One that ignores the answer gets a chipmunk, and that is its
|
||||||
|
// bug rather than ours.
|
||||||
|
val = (request == SNDCTL_DSP_SPEED) ? (int)f.rate
|
||||||
|
: (request == SNDCTL_DSP_CHANNELS) ? (int)f.channels
|
||||||
|
: AFMT_S16_LE;
|
||||||
|
if (copy_to_user(argp, &val, sizeof(val)) < 0)
|
||||||
|
return -EFAULT;
|
||||||
|
return 0;
|
||||||
|
}
|
||||||
|
|
||||||
|
case SNDCTL_DSP_SYNC:
|
||||||
|
audio_drain();
|
||||||
|
return 0;
|
||||||
|
|
||||||
|
case SNDCTL_DSP_RESET:
|
||||||
|
audio_stop();
|
||||||
|
return 0;
|
||||||
|
|
||||||
|
case SNDCTL_DSP_GETOSPACE: {
|
||||||
|
struct audio_buf_info bi;
|
||||||
|
int space = o->space ? o->space(d) : 0;
|
||||||
|
|
||||||
|
bi.fragsize = 4096;
|
||||||
|
bi.bytes = space;
|
||||||
|
bi.fragments = space / bi.fragsize;
|
||||||
|
bi.fragstotal = 0;
|
||||||
|
if (copy_to_user(argp, &bi, sizeof(bi)) < 0)
|
||||||
|
return -EFAULT;
|
||||||
|
return 0;
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
return -ENOTTY;
|
||||||
|
}
|
||||||
|
|
@ -211,4 +211,8 @@ struct devsw devsw[] = {
|
||||||
// reverse of major 9: that hands a device to a process, this lets a process
|
// reverse of major 9: that hands a device to a process, this lets a process
|
||||||
// be one. See include/netuser.h.
|
// be one. See include/netuser.h.
|
||||||
[11] = { netuser_read, netuser_write, netuser_ready },
|
[11] = { netuser_read, netuser_write, netuser_ready },
|
||||||
|
// /dev/dsp (major 12) -- UNIX audio, kernel/dev/audio.c. Write PCM to it.
|
||||||
|
// The close hook plays out what is still queued: a program that writes a
|
||||||
|
// sound and exits expects to hear the end of it.
|
||||||
|
[12] = { dspread, dspwrite, 0, dspclose },
|
||||||
};
|
};
|
||||||
|
|
|
||||||
|
|
@ -40,6 +40,7 @@ static const char *class_names[DEVCLASS_NCLASS] = {
|
||||||
[DEVCLASS_STORAGE] = "storage",
|
[DEVCLASS_STORAGE] = "storage",
|
||||||
[DEVCLASS_NET] = "net",
|
[DEVCLASS_NET] = "net",
|
||||||
[DEVCLASS_BUS] = "bus",
|
[DEVCLASS_BUS] = "bus",
|
||||||
|
[DEVCLASS_AUDIO] = "audio",
|
||||||
};
|
};
|
||||||
|
|
||||||
const char *
|
const char *
|
||||||
|
|
|
||||||
|
|
@ -365,6 +365,7 @@ pci_class_of(const struct pci_dev *d)
|
||||||
case PCI_CLASS_STORAGE: return DEVCLASS_STORAGE;
|
case PCI_CLASS_STORAGE: return DEVCLASS_STORAGE;
|
||||||
case PCI_CLASS_NETWORK: return DEVCLASS_NET;
|
case PCI_CLASS_NETWORK: return DEVCLASS_NET;
|
||||||
case PCI_CLASS_SERIAL_BUS: return DEVCLASS_BUS;
|
case PCI_CLASS_SERIAL_BUS: return DEVCLASS_BUS;
|
||||||
|
case PCI_CLASS_MULTIMEDIA: return DEVCLASS_AUDIO;
|
||||||
default: return DEVCLASS_OTHER;
|
default: return DEVCLASS_OTHER;
|
||||||
}
|
}
|
||||||
}
|
}
|
||||||
|
|
|
||||||
413
kernel/drivers/audio/ac97.c
Normal file
413
kernel/drivers/audio/ac97.c
Normal file
|
|
@ -0,0 +1,413 @@
|
||||||
|
// AC'97, the audio class's first driver.
|
||||||
|
//
|
||||||
|
// Written from the Intel 82801 datasheet's audio chapter. It is the simplest
|
||||||
|
// PC audio device that exists on real machines and in QEMU both, which is why
|
||||||
|
// it is first: the point of this driver is to prove the class and /dev/dsp
|
||||||
|
// with the least chip-specific code possible. Intel HDA -- which is what a
|
||||||
|
// laptop built this century actually has -- is a much larger driver, and
|
||||||
|
// writing it against an interface nothing had ever played a sound through
|
||||||
|
// would be writing two unproven things at once.
|
||||||
|
//
|
||||||
|
// Two register files, both **I/O ports** rather than MMIO:
|
||||||
|
//
|
||||||
|
// NAM BAR0, the mixer. Volume, and the codec's own capabilities.
|
||||||
|
// NABM BAR1, bus mastering. The descriptor list, and the DMA engine that
|
||||||
|
// walks it.
|
||||||
|
//
|
||||||
|
// The DMA engine reads a *buffer descriptor list*: 32 entries, each naming a
|
||||||
|
// physical address and a length in samples. It plays entry CIV, and stops when
|
||||||
|
// it reaches LVI -- the "last valid index". Playing continuously is therefore
|
||||||
|
// not a matter of starting it and walking away; it is a matter of keeping LVI
|
||||||
|
// ahead of CIV, which is what queue() does.
|
||||||
|
|
||||||
|
#include "types.h"
|
||||||
|
#include "defs.h"
|
||||||
|
#include "param.h"
|
||||||
|
#include "x86.h"
|
||||||
|
#include "spinlock.h"
|
||||||
|
#include "sleeplock.h"
|
||||||
|
#include "fs.h"
|
||||||
|
#include "file.h"
|
||||||
|
#include "memlayout.h"
|
||||||
|
#include "mmu.h"
|
||||||
|
#include "pci.h"
|
||||||
|
#include "device.h"
|
||||||
|
#include "audio.h"
|
||||||
|
#include "dma.h"
|
||||||
|
#include "irq.h"
|
||||||
|
|
||||||
|
// --- NAM, the mixer ---------------------------------------------------------
|
||||||
|
|
||||||
|
#define NAM_RESET 0x00
|
||||||
|
#define NAM_MASTER_VOL 0x02
|
||||||
|
#define NAM_PCM_OUT_VOL 0x18
|
||||||
|
#define NAM_EXT_ID 0x28
|
||||||
|
#define NAM_EXT_CTRL 0x2A
|
||||||
|
#define NAM_PCM_FRONT_RATE 0x2C
|
||||||
|
|
||||||
|
#define EXT_VRA 0x0001 // variable rate: the codec can do 44100
|
||||||
|
|
||||||
|
// --- NABM, the bus master ---------------------------------------------------
|
||||||
|
//
|
||||||
|
// The PCM *out* box starts at 0x10. There are three boxes (in, out, mic) and
|
||||||
|
// they have the same shape, which is why the offsets below are written as a
|
||||||
|
// base plus a field rather than as constants.
|
||||||
|
|
||||||
|
#define PO_BASE 0x10
|
||||||
|
#define PO_BDBAR (PO_BASE + 0x00) // uint32: physical address of the list
|
||||||
|
#define PO_CIV (PO_BASE + 0x04) // uint8: entry being played now
|
||||||
|
#define PO_LVI (PO_BASE + 0x05) // uint8: last entry the engine may play
|
||||||
|
#define PO_SR (PO_BASE + 0x06) // uint16: status
|
||||||
|
#define PO_PICB (PO_BASE + 0x08) // uint16: samples left in this entry
|
||||||
|
#define PO_CR (PO_BASE + 0x0B) // uint8: control
|
||||||
|
|
||||||
|
#define CR_RPBM 0x01 // run
|
||||||
|
#define CR_RR 0x02 // reset the box
|
||||||
|
#define CR_IOCE 0x10 // interrupt on completion
|
||||||
|
|
||||||
|
#define SR_DCH 0x01 // DMA halted
|
||||||
|
#define SR_BCIS 0x08 // buffer completion interrupt
|
||||||
|
#define SR_LVBCI 0x04 // last valid buffer played
|
||||||
|
|
||||||
|
#define GLOB_CTRL 0x2C
|
||||||
|
#define GLOB_STA 0x30
|
||||||
|
|
||||||
|
// --- the ring ---------------------------------------------------------------
|
||||||
|
//
|
||||||
|
// 32 descriptors of 4 KB each: 128 KB, which at 48 kHz stereo is about
|
||||||
|
// two thirds of a second. Long enough that a writer can fall behind for a
|
||||||
|
// scheduling quantum without a gap, short enough that stopping is prompt.
|
||||||
|
|
||||||
|
#define NDESC 32
|
||||||
|
#define DESC_BYTES 4096
|
||||||
|
|
||||||
|
struct bdl_entry {
|
||||||
|
uint32 addr;
|
||||||
|
uint16 samples; // *samples*, not bytes: 16-bit words, so bytes/2
|
||||||
|
uint16 flags;
|
||||||
|
};
|
||||||
|
|
||||||
|
#define BDL_IOC 0x8000 // interrupt when this one finishes
|
||||||
|
|
||||||
|
struct ac97 {
|
||||||
|
uint16 nam, nabm; // I/O port bases
|
||||||
|
struct bdl_entry *bdl; // NDESC entries, DMA memory
|
||||||
|
uint8 *buf; // NDESC * DESC_BYTES, DMA memory
|
||||||
|
uint32 bdl_phys, buf_phys;
|
||||||
|
|
||||||
|
int head; // next descriptor to fill
|
||||||
|
int tail; // oldest one still queued
|
||||||
|
int filled[NDESC]; // bytes in each, 0 when free
|
||||||
|
int running;
|
||||||
|
struct spinlock lock;
|
||||||
|
struct pci_dev *pdev;
|
||||||
|
};
|
||||||
|
|
||||||
|
static struct ac97 ac97dev;
|
||||||
|
|
||||||
|
static struct ac97 *
|
||||||
|
of(struct device *d)
|
||||||
|
{
|
||||||
|
(void)d;
|
||||||
|
return ac97dev.nabm ? &ac97dev : 0;
|
||||||
|
}
|
||||||
|
|
||||||
|
// --- mixer ------------------------------------------------------------------
|
||||||
|
|
||||||
|
// Volume is attenuation: 0 is loudest, and the mute bit is 0x8000. Writing 0
|
||||||
|
// rather than a "sensible" level on purpose -- the kernel has no business
|
||||||
|
// deciding how loud a machine is, and a device that comes up silent reads as
|
||||||
|
// broken to whoever is testing it.
|
||||||
|
static void
|
||||||
|
mixer_init(struct ac97 *a)
|
||||||
|
{
|
||||||
|
outw(a->nam + NAM_RESET, 0);
|
||||||
|
outw(a->nam + NAM_MASTER_VOL, 0x0000);
|
||||||
|
outw(a->nam + NAM_PCM_OUT_VOL, 0x0000);
|
||||||
|
}
|
||||||
|
|
||||||
|
// --- the class ops ----------------------------------------------------------
|
||||||
|
|
||||||
|
static int
|
||||||
|
ac97_configure(struct device *d, struct audio_format *f)
|
||||||
|
{
|
||||||
|
struct ac97 *a = of(d);
|
||||||
|
uint16 ext;
|
||||||
|
|
||||||
|
if (!a)
|
||||||
|
return -1;
|
||||||
|
|
||||||
|
// Two channels always. AC'97 plays stereo; a mono stream would have to be
|
||||||
|
// doubled, and doing that in the driver would hide it from the caller that
|
||||||
|
// asked -- which is what the write-back in the ioctl is for.
|
||||||
|
f->channels = 2;
|
||||||
|
f->bits = AUDIO_FMT_S16LE;
|
||||||
|
|
||||||
|
ext = inw(a->nam + NAM_EXT_ID);
|
||||||
|
if (ext & EXT_VRA) {
|
||||||
|
outw(a->nam + NAM_EXT_CTRL, inw(a->nam + NAM_EXT_CTRL) | EXT_VRA);
|
||||||
|
outw(a->nam + NAM_PCM_FRONT_RATE, (uint16)f->rate);
|
||||||
|
// What the codec settled on, which is not always what was asked: it is
|
||||||
|
// entitled to round to something it can generate.
|
||||||
|
f->rate = inw(a->nam + NAM_PCM_FRONT_RATE);
|
||||||
|
} else {
|
||||||
|
// No variable rate. 48 kHz is the only thing this codec plays, and saying
|
||||||
|
// so is more useful than accepting 44100 and playing it 9% fast.
|
||||||
|
f->rate = 48000;
|
||||||
|
}
|
||||||
|
|
||||||
|
return 0;
|
||||||
|
}
|
||||||
|
|
||||||
|
// How many descriptors the engine has finished with.
|
||||||
|
// Descriptors with nothing in them, counted forward from where the next write
|
||||||
|
// would go. Stops at the first one still holding audio, which is what makes
|
||||||
|
// this the number of bytes a write can take without waiting.
|
||||||
|
static int
|
||||||
|
free_descs(struct ac97 *a)
|
||||||
|
{
|
||||||
|
int n = 0;
|
||||||
|
|
||||||
|
for (int i = 0; i < NDESC; i++) {
|
||||||
|
if (a->filled[(a->head + i) % NDESC])
|
||||||
|
break;
|
||||||
|
n++;
|
||||||
|
}
|
||||||
|
return n;
|
||||||
|
}
|
||||||
|
|
||||||
|
static int
|
||||||
|
ac97_space(struct device *d)
|
||||||
|
{
|
||||||
|
struct ac97 *a = of(d);
|
||||||
|
int n;
|
||||||
|
|
||||||
|
if (!a)
|
||||||
|
return 0;
|
||||||
|
acquire(&a->lock);
|
||||||
|
n = free_descs(a) * DESC_BYTES;
|
||||||
|
release(&a->lock);
|
||||||
|
return n;
|
||||||
|
}
|
||||||
|
|
||||||
|
static int
|
||||||
|
ac97_queue(struct device *d, const void *pcm, int bytes)
|
||||||
|
{
|
||||||
|
struct ac97 *a = of(d);
|
||||||
|
int civ, idx, take;
|
||||||
|
|
||||||
|
if (!a)
|
||||||
|
return -1;
|
||||||
|
|
||||||
|
acquire(&a->lock);
|
||||||
|
|
||||||
|
civ = inb(a->nabm + PO_CIV) % NDESC;
|
||||||
|
idx = a->head;
|
||||||
|
|
||||||
|
// Retire what the engine has finished with.
|
||||||
|
//
|
||||||
|
// `tail` is the oldest descriptor we still believe is queued; CIV is the one
|
||||||
|
// being played. Everything between them is done. Doing this here as well as
|
||||||
|
// in the interrupt handler is deliberate -- the handler is an optimisation,
|
||||||
|
// and audio that only works when its interrupt arrives is audio that stops
|
||||||
|
// dead on a machine whose line is misrouted.
|
||||||
|
while (a->tail != civ && a->filled[a->tail]) {
|
||||||
|
a->filled[a->tail] = 0;
|
||||||
|
a->tail = (a->tail + 1) % NDESC;
|
||||||
|
}
|
||||||
|
|
||||||
|
if (a->filled[idx]) {
|
||||||
|
release(&a->lock);
|
||||||
|
return 0; // ring full
|
||||||
|
}
|
||||||
|
|
||||||
|
take = bytes > DESC_BYTES ? DESC_BYTES : bytes;
|
||||||
|
memmove(a->buf + (uint64)idx * DESC_BYTES, pcm, take);
|
||||||
|
|
||||||
|
a->bdl[idx].addr = a->buf_phys + (uint32)idx * DESC_BYTES;
|
||||||
|
a->bdl[idx].samples = (uint16)(take / 2); // 16-bit words
|
||||||
|
a->bdl[idx].flags = BDL_IOC;
|
||||||
|
a->filled[idx] = take;
|
||||||
|
a->head = (idx + 1) % NDESC;
|
||||||
|
|
||||||
|
// LVI is the last entry the engine may play. Keeping it at the descriptor
|
||||||
|
// just written is what makes this a queue rather than a one-shot.
|
||||||
|
outb(a->nabm + PO_LVI, (uint8)idx);
|
||||||
|
|
||||||
|
release(&a->lock);
|
||||||
|
return take;
|
||||||
|
}
|
||||||
|
|
||||||
|
static void
|
||||||
|
ac97_start(struct device *d)
|
||||||
|
{
|
||||||
|
struct ac97 *a = of(d);
|
||||||
|
|
||||||
|
if (!a)
|
||||||
|
return;
|
||||||
|
acquire(&a->lock);
|
||||||
|
if (!a->running) {
|
||||||
|
outb(a->nabm + PO_CR, CR_RPBM | CR_IOCE);
|
||||||
|
a->running = 1;
|
||||||
|
}
|
||||||
|
release(&a->lock);
|
||||||
|
}
|
||||||
|
|
||||||
|
static void
|
||||||
|
ac97_stop(struct device *d)
|
||||||
|
{
|
||||||
|
struct ac97 *a = of(d);
|
||||||
|
|
||||||
|
if (!a)
|
||||||
|
return;
|
||||||
|
acquire(&a->lock);
|
||||||
|
outb(a->nabm + PO_CR, 0);
|
||||||
|
outb(a->nabm + PO_CR, CR_RR); // reset the box: CIV, LVI, PICB to 0
|
||||||
|
for (int i = 0; i < NDESC; i++)
|
||||||
|
a->filled[i] = 0;
|
||||||
|
a->head = 0;
|
||||||
|
a->tail = 0;
|
||||||
|
a->running = 0;
|
||||||
|
release(&a->lock);
|
||||||
|
}
|
||||||
|
|
||||||
|
static int
|
||||||
|
ac97_pending(struct device *d)
|
||||||
|
{
|
||||||
|
struct ac97 *a = of(d);
|
||||||
|
int n = 0;
|
||||||
|
|
||||||
|
if (!a)
|
||||||
|
return 0;
|
||||||
|
acquire(&a->lock);
|
||||||
|
if (a->running && !(inw(a->nabm + PO_SR) & SR_DCH)) {
|
||||||
|
for (int i = 0; i < NDESC; i++)
|
||||||
|
if (a->filled[i])
|
||||||
|
n += a->filled[i];
|
||||||
|
}
|
||||||
|
release(&a->lock);
|
||||||
|
return n;
|
||||||
|
}
|
||||||
|
|
||||||
|
static const struct audio_ops ac97_ops = {
|
||||||
|
.configure = ac97_configure,
|
||||||
|
.space = ac97_space,
|
||||||
|
.queue = ac97_queue,
|
||||||
|
.start = ac97_start,
|
||||||
|
.stop = ac97_stop,
|
||||||
|
.pending = ac97_pending,
|
||||||
|
};
|
||||||
|
|
||||||
|
// --- interrupt --------------------------------------------------------------
|
||||||
|
|
||||||
|
static void
|
||||||
|
ac97_intr(void *arg)
|
||||||
|
{
|
||||||
|
struct ac97 *a = arg;
|
||||||
|
uint16 sr;
|
||||||
|
|
||||||
|
if (!a || !a->nabm)
|
||||||
|
return;
|
||||||
|
|
||||||
|
sr = inw(a->nabm + PO_SR);
|
||||||
|
|
||||||
|
// Acknowledge by writing the bits back. A status bit left set on a
|
||||||
|
// level-triggered line is an interrupt that re-fires for ever -- the same
|
||||||
|
// shape as the e1000 bug in docs/history/kernel.md section 13.
|
||||||
|
if (sr & (SR_BCIS | SR_LVBCI | SR_DCH))
|
||||||
|
outw(a->nabm + PO_SR, sr & (SR_BCIS | SR_LVBCI | SR_DCH));
|
||||||
|
|
||||||
|
{
|
||||||
|
int civ = inb(a->nabm + PO_CIV) % NDESC;
|
||||||
|
|
||||||
|
// Everything the engine has passed is free again. Through `tail` rather
|
||||||
|
// than by clearing one entry, so this and ac97_queue() cannot disagree
|
||||||
|
// about which descriptors are in flight.
|
||||||
|
while (a->tail != civ && a->filled[a->tail]) {
|
||||||
|
a->filled[a->tail] = 0;
|
||||||
|
a->tail = (a->tail + 1) % NDESC;
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
// The writer is asleep on the tick rather than on this device, so there is
|
||||||
|
// nothing to wake -- see audio_wait(). Keeping the handler to "acknowledge
|
||||||
|
// and account" is deliberate: an interrupt handler that can be deleted
|
||||||
|
// without the audio stopping is one that cannot deadlock the audio either.
|
||||||
|
}
|
||||||
|
|
||||||
|
// --- probe ------------------------------------------------------------------
|
||||||
|
|
||||||
|
static int
|
||||||
|
ac97_probe(struct pci_dev *d)
|
||||||
|
{
|
||||||
|
struct ac97 *a = &ac97dev;
|
||||||
|
|
||||||
|
if (a->nabm)
|
||||||
|
return -1; // one is enough
|
||||||
|
|
||||||
|
// Both BARs are I/O ports on this device, which is why nothing here maps
|
||||||
|
// anything: `is_io` is what says so, and a driver that ioremapped these
|
||||||
|
// would be mapping a port number as if it were an address.
|
||||||
|
if (!d->bar[0].is_io || !d->bar[1].is_io ||
|
||||||
|
!d->bar[0].base || !d->bar[1].base) {
|
||||||
|
cprintf("ac97: expected two I/O BARs; not driving this device\n");
|
||||||
|
return -1;
|
||||||
|
}
|
||||||
|
|
||||||
|
a->nam = (uint16)d->bar[0].base;
|
||||||
|
a->nabm = (uint16)d->bar[1].base;
|
||||||
|
a->pdev = d;
|
||||||
|
initlock(&a->lock, "ac97");
|
||||||
|
|
||||||
|
pci_enable(d, PCI_CMD_IO | PCI_CMD_BUS_MASTER);
|
||||||
|
|
||||||
|
// The descriptor list and the audio itself, both from the DMA arena: the
|
||||||
|
// engine reads them by physical address, and kalloc's pages are adjacent
|
||||||
|
// only by chance.
|
||||||
|
a->bdl = dma_alloc(NDESC * sizeof(struct bdl_entry), 4096);
|
||||||
|
a->buf = dma_alloc(NDESC * DESC_BYTES, 4096);
|
||||||
|
if (!a->bdl || !a->buf) {
|
||||||
|
cprintf("ac97: no DMA memory for a %d KB ring\n",
|
||||||
|
(NDESC * DESC_BYTES) / 1024);
|
||||||
|
a->nabm = 0;
|
||||||
|
return -1;
|
||||||
|
}
|
||||||
|
a->bdl_phys = (uint32)dma_phys(a->bdl);
|
||||||
|
a->buf_phys = (uint32)dma_phys(a->buf);
|
||||||
|
memset(a->bdl, 0, NDESC * sizeof(struct bdl_entry));
|
||||||
|
memset(a->buf, 0, NDESC * DESC_BYTES);
|
||||||
|
|
||||||
|
// Cold reset of the whole controller, then the PCM-out box.
|
||||||
|
outl(a->nabm + GLOB_CTRL, 0x00000002);
|
||||||
|
mixer_init(a);
|
||||||
|
outb(a->nabm + PO_CR, CR_RR);
|
||||||
|
for (int spin = 0; spin < 100000 && (inb(a->nabm + PO_CR) & CR_RR); spin++)
|
||||||
|
;
|
||||||
|
|
||||||
|
outl(a->nabm + PO_BDBAR, a->bdl_phys);
|
||||||
|
|
||||||
|
if (d->irq != 0xFF && d->irq < 24)
|
||||||
|
irq_register(d->irq, ac97_intr, a, "ac97", 1);
|
||||||
|
|
||||||
|
kinfo("ac97: nam %x nabm %x, %d KB ring, irq %d\n",
|
||||||
|
a->nam, a->nabm, (NDESC * DESC_BYTES) / 1024, d->irq);
|
||||||
|
return 0;
|
||||||
|
}
|
||||||
|
|
||||||
|
static const struct pci_match ac97_match[] = {
|
||||||
|
{ 0x8086, 0x2415, 0, 0 }, // 82801AA, which is what QEMU's -device AC97 is
|
||||||
|
{ 0x8086, 0x2425, 0, 0 }, // 82801AB
|
||||||
|
{ 0x8086, 0x2445, 0, 0 }, // 82801BA
|
||||||
|
{ 0x8086, 0x24C5, 0, 0 }, // ICH4
|
||||||
|
{ 0x8086, 0x24D5, 0, 0 }, // ICH5
|
||||||
|
{ 0x8086, 0x266E, 0, 0 }, // ICH6
|
||||||
|
{ 0, 0, 0, 0 },
|
||||||
|
};
|
||||||
|
|
||||||
|
const struct pci_driver ac97_driver = {
|
||||||
|
.name = "ac97",
|
||||||
|
.devname = "audio",
|
||||||
|
.match = ac97_match,
|
||||||
|
.ops = &ac97_ops,
|
||||||
|
.probe = ac97_probe,
|
||||||
|
};
|
||||||
|
|
@ -32,6 +32,7 @@ extern const struct pci_driver vga_pci_driver;
|
||||||
extern const struct pci_driver xhci_driver;
|
extern const struct pci_driver xhci_driver;
|
||||||
extern const struct pci_driver virtio_gpu_driver;
|
extern const struct pci_driver virtio_gpu_driver;
|
||||||
extern const struct pci_driver e1000_driver;
|
extern const struct pci_driver e1000_driver;
|
||||||
|
extern const struct pci_driver ac97_driver;
|
||||||
|
|
||||||
// Order matters here in one respect: virtio-gpu is offered the bus before the
|
// Order matters here in one respect: virtio-gpu is offered the bus before the
|
||||||
// VBE framebuffer driver, so that on a machine with both, the device with real
|
// VBE framebuffer driver, so that on a machine with both, the device with real
|
||||||
|
|
@ -43,6 +44,7 @@ static const struct pci_driver *drivers[] = {
|
||||||
&vga_pci_driver,
|
&vga_pci_driver,
|
||||||
&e1000_driver,
|
&e1000_driver,
|
||||||
&xhci_driver,
|
&xhci_driver,
|
||||||
|
&ac97_driver,
|
||||||
};
|
};
|
||||||
|
|
||||||
void
|
void
|
||||||
|
|
|
||||||
|
|
@ -96,6 +96,8 @@ static const struct devnode devnodes[] = {
|
||||||
// include/dbg.h and cmd/schdbgd.
|
// include/dbg.h and cmd/schdbgd.
|
||||||
{ "dbgro", 10, 1, D_ROOT },
|
{ "dbgro", 10, 1, D_ROOT },
|
||||||
{ "netdev", 11, 0, D_ROOT },
|
{ "netdev", 11, 0, D_ROOT },
|
||||||
|
// Audio, spelled the way UNIX spells it. See include/audio.h.
|
||||||
|
{ "dsp", 12, 0, D_ROOT },
|
||||||
{ "mouse", 3, 1, D_ROOT },
|
{ "mouse", 3, 1, D_ROOT },
|
||||||
|
|
||||||
// Raw disks. Created whether or not a drive is present: opening one with no
|
// Raw disks. Created whether or not a drive is present: opening one with no
|
||||||
|
|
|
||||||
|
|
@ -1286,6 +1286,8 @@ addr_t sys_ioctl(void)
|
||||||
return pciuser_ioctl(request, argp);
|
return pciuser_ioctl(request, argp);
|
||||||
if (is_dev && f->ip->major == NETUSER_MAJOR)
|
if (is_dev && f->ip->major == NETUSER_MAJOR)
|
||||||
return netuser_ioctl(request, argp);
|
return netuser_ioctl(request, argp);
|
||||||
|
if (is_dev && f->ip->major == AUDIO_MAJOR)
|
||||||
|
return dsp_ioctl((int)request, argp);
|
||||||
|
|
||||||
int is_tty = (is_dev && f->ip->major == 1);
|
int is_tty = (is_dev && f->ip->major == 1);
|
||||||
if (!is_tty) {
|
if (!is_tty) {
|
||||||
|
|
|
||||||
Loading…
Reference in a new issue