Re: [Qemu-devel] [PATCH 5/6] [RFC] Emulation of Leon3.

[Edgar E. Iglesias]

On Fri, Dec 17, 2010 at 07:14:20PM +0000, Blue Swirl wrote:
> On Wed, Dec 15, 2010 at 5:47 PM, Fabien Chouteau <address@hidden> wrote:
> > On 12/13/2010 07:18 PM, Blue Swirl wrote:
> >>
> >> On Mon, Dec 13, 2010 at 3:51 PM, Fabien Chouteau<address@hidden>
> >>  wrote:
> >>>
> >>> On 12/11/2010 10:56 AM, Blue Swirl wrote:
> >>>>
> >>>> On Tue, Dec 7, 2010 at 11:40 AM, Fabien Chouteau<address@hidden>
> >>>>  wrote:
> >>>>>
> >>>>> On 12/06/2010 06:53 PM, Blue Swirl wrote:
> >>>>>>
> >>>>>> On Mon, Dec 6, 2010 at 9:26 AM, Fabien Chouteau<address@hidden>
> >>>>>>  wrote:
> >>>>>>>
> >>>>>>> Signed-off-by: Fabien Chouteau<address@hidden>
> >>>>>>> ---

...

> >>>>>>>  #ifdef DEBUG_PCALL
> >>>>>>>     if (qemu_loglevel_mask(CPU_LOG_INT)) {
> >>>>>>>         static int count;
> >>>>>>> @@ -4135,6 +4153,14 @@ void do_interrupt(CPUState *env)
> >>>>>>>     env->pc = env->tbr;
> >>>>>>>     env->npc = env->pc + 4;
> >>>>>>>     env->exception_index = -1;
> >>>>>>> +
> >>>>>>> +#if !defined(CONFIG_USER_ONLY)
> >>>>>>> +    /* IRQ acknowledgment for Leon3 */
> >>>>>>> +    if (env->version == 0xf3000000&&      (intno&      ~15) ==
> >>>>>>> TT_EXTINT)
> >>>>>>> {
> >>>>>>> +        grlib_irqmp_ack (env, intno);
> >>>>>>> +        leon3_cache_control_int();
> >>>>>>> +    }
> >>>>>>
> >>>>>> Like this. I don't think a CPU should immediately ack any incoming
> >>>>>> interrupts.
> >>>>>
> >>>>> Leon3 does...
> >>>>
> >>>> Strange. Then this should be handled at board level (leon3.c).
> >>>
> >>> Well, it's a CPU feature not a board feature.
> >>
> >> Maybe, but we don't want to clutter interrupt handling with this.
> >
> > I don't see what you expect here... How can I get the acknowledgment
> > information without changing the do_interrupt function?
> 
> Board can acknowledge the interrupt just before calling cpu_interrupt().

Hi,

I don't think that will work properly. IIUC, the leon acks the irq when it
is actually taken by the CPU. Due to CPU internal masking, that may be at
a later point than when the irq is signalled to the CPU.

IMO, what is needed is something along the lines of what Fabien coded but
with some level of indirection so that the CPU doesn't call directly into
the irqmp model. Maybe through ack function pointers or through a
qemu_irq ack line or some other way. The board should then setup the
connection between the ack mechanism and the irqmp model.

Cheers