etc:users:jcmvbkbc:little-things:4
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Table of Contents
2010-01-04 Qemu PCI card with IRQ
Plan
- Find the right way of triggering IRQ through PCI:
- when to assert, when to deassert IRQ line;
- when to start, when to cease interrupting;
- Make PCI device driver that would handle IRQs;
Worklog
Conclusion
- when to assert/deassert IRQ line: no matter (at least for emulation);
- although it is generally level-triggered, qemu treats them as edge-triggered, so that qemu_irq_pulse may be used;
- anyway (e.g. for proper IRQ sharing) separate 'irq status' register is needed for the device function (not implemented in this demo, but hold on :);
- when to start/stop interrupts: doc contradiction;
- PCI spec says that IRQ is enabled (interrupt disable == 0 in command register) upon reset, but linux pci documentation says that IRQ will go only when you explicitly enable them;
- anyway, nothing happens (at least, nothing is visible) until request_irq;
- even more: right place to request_irq is not probe routine, but rather device open routine;
- qemu 0.12.1 yields maximum of ~3000 PCI interrupts/second;
- using tabs in Linux is stupid ):
etc/users/jcmvbkbc/little-things/4.1262833859.txt.gz · Last modified: 2010/01/07 06:10 by jcmvbkbc