Re: [PATCH 8/8] q800: add NMI handler

[Mark Cave-Ayland]

On 16/10/2021 18:09, Laurent Vivier wrote:

> Le 15/10/2021 à 22:12, Mark Cave-Ayland a écrit :
> > On 15/10/2021 09:40, Laurent Vivier wrote:
> >
> > > Le 13/10/2021 à 23:21, Mark Cave-Ayland a écrit :
> > > > This allows the programmer's switch to be triggered via the monitor for 
> > > > debugging
> > > > purposes. Since the CPU level 7 interrupt is level-triggered, use a timer to 
> > > > hold
> > > > the NMI active for 100ms before releasing it again.
> > >
> > > I'm wondering if Qemu provides another way to have a level-triggered interrupt 
> > > in this case.
> > >
> > > I' tried to see if keeping the button pressed on a mac kept the IRQ up (as QMP 
> > > NMI does), but a real
> > > mac is too slow and has to many things to display it was not really 
> > > conclusive...
> >
> > When writing the patch I rebased the outstanding MacOS patches onto the branch, 
> > installed Macsbug
> > into MacOS and used "info nmi" to break into it.
> >
> > Testing glue_nmi() with:
> >
> >    GLUE_set_irq(s, GLUE_IRQ_IN_NMI, 1);
> >    GLUE_set_irq(s, GLUE_IRQ_IN_NMI, 0);
> >
> > i.e. a simple pulse didn't launch MacsBug at all. Keeping the NMI high launches 
> > MacsBug (which is
> > usable) but then as soon as you exit MacsBug with ES, MacsBug breaks 
> > immediately again making it
> > impossible to return to the Finder. Adding the timer allows launching MacsBug 
> > and then
> > exiting/re-entering MacsBug again on demand as expected.
>
> I think we have to mimic the finger pressing the button..
>
> By the way, NMI should also dumps the CPU registers under linux.
>
> Reviewied-by: Laurent Vivier <laurent@vivier.eu>

I've just tried this on Linux, and it seems to work okay although I get several 
copies of the register dump on the console for a single invocation of "info nmi" e.g.

[    4.610000] Non-Maskable Interrupt
[    4.610000] Modules linked in: mac_esp(+) esp_scsi macsonic
[    4.610000] PC: [<00002dc0>] arch_cpu_idle+0x4/0x6
[    4.610000] SR: 2000  SP: (ptrval)  a2: 00395314
[    4.610000] d0: 00000000    d1: 00000002    d2: 0004b492    d3: 00392000
[    4.610000] d4: 00000000    d5: 00000000    a0: 00392000    a1: 00395314
[    4.610000] Process swapper (pid: 0, task=(ptrval))
[    4.610000] Frame format=0
[    4.610000] Stack from 00393f9c:
[    4.610000]         0004b540 00000431 0040ee22 0004b4c4 0002bf6a 004005f0 00393ff8 
0004b714
[    4.610000]         0003e23a 0029c518 000000c2 0040eb54 3dc1e5d0 00000000 0004ff74 
0003efe2
[    4.610000]         003f4e92 00000000 00000040 00000000 00000000 00000000 0040ee22 
00000000
[    4.610000]         003f3872
[    4.610000] Call Trace: [<0004b540>] do_idle+0x7c/0xd2
[    4.610000]  [<0004b4c4>] do_idle+0x0/0xd2
[    4.610000]  [<0002bf6a>] kernel_thread+0x0/0x26
[    4.610000]  [<004005f0>] __alloc_bootmem+0x0/0x38
[    4.610000]  [<0004b714>] cpu_startup_entry+0xe/0x12
[    4.610000]  [<0003e23a>] find_task_by_pid_ns+0x0/0x22
[    4.610000]  [<0029c518>] rest_init+0x78/0x82
[    4.610000]  [<0004ff74>] printk+0x0/0x18
[    4.610000]  [<0003efe2>] parse_args+0x0/0x2c2
[    4.610000]  [<003f4e92>] start_kernel+0x43e/0x448
[    4.610000]  [<003f3872>] _sinittext+0x872/0x11f8
[    4.610000] Code: bc00 0060 f210 f0ff 7001 60cc 4e72 2000 <4e75> 2079 003b fc6c 
4a88 6702 4e90 60fe 2079 003b fc68 4a88 6702 4e90 60fe 2f0c

(repeated 7 or 8 times)

MacsBug seems to handle this better: as soon as the NMI is triggered, MacsBug opens 
and displays "NMI" both if the programmer switch GPIO is held active, or pulsed as 
implemented in the patch. When using the above patch, subsequent NMI triggers do not 
display "NMI" or change MacsBug in any visible way which suggests that once the NMI 
is triggered, the NMI is ignored until the programmers switch GPIO is inactive once 
again.

Do you see the repeated register output in Linux for a single press of the 
programmers switch on a real Quadra 800? It may be that Linux could be improved by 
having similar logic.


ATB,

Mark.