3182da3965
Claude Code keeps per-project memory at <home>/.claude/projects/<key>/,
where <key> is the project's absolute path with every separator and the
drive colon turned into a dash. That makes it both rename-fragile and
machine-specific, and this project has hit each of those once:
- D:\DEV\Schunix -> D:\DEV\SchOS changed the key, and 43 memories were
invisible until moved across by hand.
- Development happens from Windows and from Linux, and each looks in a
different place for the same checkout.
Committing .claude/memory/ fixes both -- git carries it across renames
and between hosts -- and `import` puts it wherever the local machine
expects. .claude/settings.local.json stays ignored: those are per-machine
permissions.
The colon maps to a dash rather than being dropped. Deleting it gives
D-DEV-SchOS, which matches nothing and silently finds zero memories; that
was the first attempt. On Git Bash the key comes from `cygpath -w`,
because Claude Code is a Windows program and sees D:\DEV\SchOS, not
/d/DEV/SchOS.
114 lines
5.4 KiB
Markdown
114 lines
5.4 KiB
Markdown
---
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name: schunix-e1000-and-driver-layout
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description: "The e1000 NIC driver, the drivers/ reorganisation by device class, and virtio-gpu as the QEMU default."
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metadata:
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node_type: memory
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type: project
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originSessionId: 9d8a2aef-bcf0-47a0-96c6-f706efab4a95
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modified: 2026-08-08T20:17:14.134Z
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---
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2026-08-08. Three changes, all requested by Nexoniarz in one go.
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## drivers/<class>/<driver>/
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kernel/drivers/
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registry.c the one list of what exists
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gpu/vga/ gpu/virtio_gpu/
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net/e1000/
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bus/xhci/
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usb/core/ usb/hid/ usb/storage/ usb/hub/
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One directory per *driver*, not per class (Nexoniarz asked for this
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specifically), so a driver that grows a register header, a second source file or
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a firmware blob has somewhere to put it.
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Matches `DEVCLASS_*` in `include/device.h`. Flat was eight files with four
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called `usb_something`, and each driver added made it worse.
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**Makefile note:** the compile rule is now
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`@mkdir -p $(dir $@)`, not a fixed path — a hardcoded mkdir only creates the top
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directory and every subdirectory build fails with "unable to open output file".
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`KERN_DRIVERS` is built with `+=` per class rather than one long
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`$(addprefix ...)`; scripted edits kept collapsing the line continuations.
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## virtio-gpu is the QEMU default
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`QEMU_DISPLAY = -vga std -device virtio-gpu-pci` in the Makefile, used by all
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three qemu targets. **Keep `-vga std`** — the bootloader draws the splash
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through VBE in 16-bit real mode and there is no virtio path that early, so a
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machine with only virtio-gpu boots blind until the kernel is up.
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## FreeBSD reference tree
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`Refrence/freebsd-src` (spelled that way on disk) is a full FreeBSD checkout,
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re-cloned 2026-08-08 after the NetBSD one was deleted for space. Never built,
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never in an image; recorded in `docs/layout.md` and `docs/licensing.md` §4.
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**It is 2.1 GB** — measured, and the same reason the NetBSD one was deleted.
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Only `sys/dev`, `sys/net` and `sys/netinet` have ever been read, so a sparse
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checkout (`--filter=blob:none --sparse`, then
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`sparse-checkout set sys/dev sys/net sys/netinet`) is ~100 MB and loses nothing.
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Single-file fetches from `raw.githubusercontent.com` answered every licence
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question so far and cost nothing at all.
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**`sys/dev/e1000/` is Intel BSD-3-clause with zero advertising clauses** —
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checked. Its *device ID table* was transcribed into `include/e1000.h`, taking
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the driver from binding one card (QEMU's 82540EM) to the whole 8254x family:
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82540/41/44/45/46/47, ~27 IDs. That is the shape of adoption that works —
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**data, not logic**. The driver stays written from Intel manual 317453, and
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`NOTICE` carries the Intel attribution.
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The PCIe 8257x parts (82571-82574) were deliberately *excluded*: similar
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register map, different NVM access and init. Claiming a device the driver cannot
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initialise is worse than not claiming it — it binds, reports a nonsense MAC, and
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fails for reasons that look nothing like the cause.
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## e1000
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`include/e1000.h` + `kernel/drivers/net/e1000.c`, from Intel's public manual
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317453. Worked on the first boot:
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e1000: 52:54:0:12:34:56, link up, irq 11
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**Proven to carry real traffic**, 2026-08-08: `echo n > /proc/sysrq` runs
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`e1000_selftest()`, which hand-builds an ARP request for 10.0.2.2 and waits for
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the reply. Under QEMU user-mode networking:
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e1000: asking who has 10.0.2.2
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e1000: 64 bytes from 52:55:a:0:2:2 type 806
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e1000: ARP reply -- 10.0.2.2 is at 52:55:a:0:2:2
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e1000: self-test passed, 1 tx 1 rx
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That one exchange validates the whole path: transmit descriptor format, the DD
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handshake, TDT/RDT bookkeeping, DMA addresses, the receive-ring handback, and
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**the MAC filter** -- an ARP reply is unicast to us, so a wrong RAL/RAH means it
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never arrives. SLIRP is silent until spoken to, which is why the test has to
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transmit before it can expect to receive. Do this kind of check *before*
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layering a protocol stack on a driver: otherwise the stack's first failure is
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indistinguishable from its own bugs.
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Run with `-netdev user,id=n0 -device e1000,netdev=n0`. Provides `e1000_transmit()`,
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`e1000_receive()` and the MAC — **no IP stack yet, deliberately**: a stack
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written before a driver has nothing to test against and every bug in it looks
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like a driver bug.
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Details that are easy to get wrong and are commented in the source:
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- **Set `E1000_TXD_STAT_DD` on every transmit descriptor at init.** The hardware
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only sets it after *using* one, so a driver that waits for a bit the device
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has never had reason to write waits forever.
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- **RDT starts at NRX-1, not NRX.** One descriptor must always be held back or
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"ring full" and "ring empty" are indistinguishable.
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- **Clear the multicast table.** It is undefined after reset, so left alone the
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device accepts multicast for addresses nobody asked for.
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- **Read the MAC from EEPROM *and* fall back to RAL/RAH.** Some cards leave the
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EEPROM path unimplemented and you end up with all zeroes.
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- **`irq_register(..., level_low = 1)`** — PCI interrupts are level-triggered,
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active low. Edge-configured, it fires once then wedges.
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- Rings and buffers come from `dma_alloc`; the device reads them by physical
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address and kalloc pages are contiguous only by accident.
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- Enable the receiver *after* the ring base is set, or it DMAs into physical 0,
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which on this kernel is the boot page table.
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`ops` is null on the pci_driver: there is no net class in the device model yet.
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Adding one is the natural first step when the IP stack arrives.
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