Re: [9fans] RPi in QEMU

[Don Bailey <don.bailey@gmail.com>]

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Hmm, I've applied the patches and built the kernel. I can see the image
loaded at 0x80010000, but it is spinning at address 0xffff000c; is this a
sdmmc load loop?

I'm using version 8.0.0 of QEMU. What version are you using, Mr. Miller?
Also, since the SD takes seconds to load and not ms/us, how long are you
waiting until you see something printed on the console...? Curious if I'm
just running very slow, or if there is still something buggy going on...

Thanks for responding and adding some patches. I am trying to follow along
to make it work, if you don't mind a bit of back and forth :-)

D


On Thu, Aug 31, 2023 at 2:48 PM Richard Miller <9fans@hamnavoe.com> wrote:

> don.bailey@gmail.com:
> > So to get this back on the track of RPI emulated in QEMU … has anyone
> successfully used the Miller image with Q?
>
> After a bit of experimentation, I have done so, for some value of
> "successfully".
>
> A few tweaks are required first, because QEMU's emulation of Pi hardware
> and
> firmware is not as faithful as it might be:
>
> - binary kernel file is loaded at 0x10000, not 0x8000
> - the watchdog timer doesn't work (or isn't there)
> - system timer behaviour is a bit peculiar
> - emulation of the SDMMC in multi-block mode is spectacularly slow
>   (transfers take not milliseconds but seconds)
>
> After tweaking as shown below, a QEMU-compatible kernel can be built with
>   mk CONF'='pi2 9pi2.qemu
> and run with something like
>   qemu-system-arm -M raspi2b -kernel 9pi2.qemu -serial stdio \
>     -drive file=9pi.img,if=sd,format=raw \
>     -append 'readparts=1 console=1 *ncpu=1
> nobootprompt=local!/dev/sdM0/fossil'
>
> For convenience I've put a kernel file on
> /n/sources/contrib/miller/9pi2.qemu
>
> However ...
>
> - the DWC usb host adapter of the Pi2/3 does not work the way Plan 9
> expects
> - therefore there's no functioning usb
> - therefore I don't know how to attach a keyboard, mouse or network
> interface
>
> If anybody wants to debug this further I'm happy to collaborate, but I'm
> not sufficiently motivated to do it myself.
>
> Diffs against files in /n/sources/contrib/miller/9/bcm, which I think are
> identical to 9legacy 9/bcm sources):
>
> mkfile:
> 85a86,90
> > $p$CONF.qemu:DQ:      $CONF.$O $OBJ $LIB
> >       $CC $CFLAGS '-DKERNDATE='`{date -n} $CONF.c
> >       echo '# linking kernel for QEMU'
> >       $LD -s -l -o $target -H6 -R4096 -T0x80010000 $OBJ $CONF.$O $LIB
> >
>
> mem.h:
> 48c48
> < #define       KTZERO          (KZERO+0x8000)          /* kernel text
> start */
> ---
> > #define       KTZERO          (KZERO+0x10000)         /* kernel text
> start */
>
> archbcm2.c:
> 225c225
> <       addclock0link(wdogfeed, HZ);
> ---
> >       //addclock0link(wdogfeed, 1000);
>
> sdmmc.c:
> 25c25
> <       Multiblock      = 1,
> ---
> >       Multiblock      = 0,
>
> clock.c:
> 35c35
> <       MinPeriod       = 10,
> ---
> >       MinPeriod       = 100,
> 124c124
> <       u32int t0, t1, tstart, tend;
> ---
> >       u32int t0, t1, tstart;
> 142d141
> <       tend = tstart + 10000;
> 145c144
> <       }while(tn->clo != tend);
> ---
> >       }while(tn->clo - tstart < 10000);

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