d0f7acf9eb
An x86-64 operating system built from xv6, now largely rewritten: SMP, a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF rasteriser, and a Linux-numbered syscall ABI. No history before this point -- the tree was never under version control. This commit exists so the rename that follows has something to undo to.
43 lines
2 KiB
C
43 lines
2 KiB
C
#pragma once
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// Hardware interrupt registration.
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//
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// Until this existed, trap() was a switch statement listing every interrupt
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// the kernel knew about, and adding a device meant editing the trap handler.
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// That is fine while the devices are the four the PC has always had at fixed
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// pins; it stops being fine the moment a device's IRQ is whatever the BIOS
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// decided to put in its PCI config space this boot. A driver cannot write
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// `case T_IRQ0 + IRQ_XHCI:` because there is no such constant -- it only
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// learns its line at probe time.
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//
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// So: a line has a chain of handlers, a driver adds itself to one at probe
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// time, and enabling the line is a consequence of registering rather than a
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// separate call somebody can forget.
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//
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// Chains matter more than they look. PCI interrupt pins are *shared*: four
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// INTx lines are routed to a handful of IOAPIC inputs, so two unrelated
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// devices routinely land on the same one. A handler must therefore check
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// whether its own device actually raised the interrupt and do nothing if it
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// did not.
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#define NIRQ 24 // IOAPIC redirection entries on a PC
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#define NCHAIN 4 // handlers that may share one line
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typedef void (*irq_handler_t)(void *arg);
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// Returns 0, or -1 if the line is out of range, reserved, or full.
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// Registering enables the line; the last unregister masks it again.
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//
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// `level_low` selects PCI's signalling (level-triggered, active low) rather
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// than ISA's (edge-triggered, active high). Getting this wrong does not fail
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// cleanly: an edge-configured level interrupt fires once and then wedges,
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// because the device keeps the line asserted and no further edge ever comes.
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int irq_register(int irq, irq_handler_t fn, void *arg, const char *name,
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int level_low);
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void irq_unregister(int irq, irq_handler_t fn, void *arg);
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// Called from trap() with the IOAPIC pin number, not the vector.
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void irq_dispatch(int irq);
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void irq_init(void);
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int irq_info(char *buf, int cap); // /proc/interrupts
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