Re: [9fans] RPi in QEMU

[Richard Miller <9fans@hamnavoe.com>]

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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