Re: [Qemu-devel] [RFC] IRQ acknowledge on MIPS

[Aurelien Jarno <aurelien@aurel32.net>]

Hi all,

Some news on that point.

After a discussion with Paul Brook, Thiemo Seufer and Ralf Baechle on
IRC yesterday, we got convinced that the current IRQ handling is not
correct.

The hardware interrupt is currently deasserted by the CPU itself (in
cpu-exec.c). It should be deasserted by the interrupt controller (the
i8259a in our case), so that pending interrupts are not missed. This is
wrong for MIPS, but also for x86_64 and PowerPC. ARM is correctly
implemented though.

Then after playing with the current code, I am sure we are missing a
simple interrupt controller for the MIPS CPU. It supports 6 hardware
interrupts (IP2 to IP7) and we are using two of them in the current
emulation: one for the i8259a and the other for the timer. In both case
the current code assert and deassert a CPU_INTERRUPT_HARD.

The interrupt controller should assert and deassert the
CPU_INTERRUPT_HARD upon the contents of the CP0 cause and CP0 status (ie
mask) registers. Currently we are totally ignoring that interrupts can
be masked and leave this task to the operating system.

I will try to write the missing code this night.

Bye,
Aurelien

-- 
  .''`.  Aurelien Jarno	            | GPG: 1024D/F1BCDB73
 : :' :  Debian developer           | Electrical Engineer
 `. `'   aurel32@debian.org         | aurelien@aurel32.net
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