While being a great Open Source fan, I still think it would be better to use a real machine's firmware to ensure the emulation is complete. Once we are sure the virtual hardware is working properly there will be no need to run POST. It doesn't even have to be implemented.
Otherwise there are chances that Firmware would perfectly function on a virtual hardware, but it would have nothing to do with the real hardware. There are always some features which are documented too fuzzy or not documented at all.
So I'm going to give it a shot with the real firmware. Btw it is called OBP - Open Boot Prom.
The first results are not very fruitful: the RAM is not detected, and there are no sbus devices (=> no booting from SCSI yet). But at least OBP has the command "power-off" (which OpenBIOS doesn't), and the command is even perfectly working:
$ qemu-system-sparc -M SS-20 -L . -bios ss20_v2.25_rom -nographic -hda hda.img
ESP ERROR: esp_mem_writeb: Unhandled ESP command (a2)
Power-ON Reset
SMCC SPARCstation 10/20 UP/MP POST version VRV3.45 (09/11/95)
CPU_#0 TI, STP1021PGA(1.x) 1Mb External cache
CPU_#1 ******* NOT installed *******
CPU_#2 ******* NOT installed *******
CPU_#3 ******* NOT installed *******
<<<>>> IS RUNNING (MID = 00000008)
$$$$$ WARNING : No Keyboard Detected! $$$$$
MMU ICACHE_TLB bit pattern Test
Case 0000000f: I_TLB mis-matched exp=55555000 obs=00000000 xor=
55555000 entry # 0x00000000
Available Memory 0x08000000
Allocating SRMMU Context Table
Context Table allocated, Available Memory 0x07fc0000
Setting SRMMU Context Register
Context Table allocated, Available Memory 0x07fc0000
Setting SRMMU Context Table Pointer Register
RAMsize allocated, Available Memory 0x07fb0000
Allocating SRMMU Level 1 Table
Level 1 Table allocated, Available Memory 0x07fafc00
Mapping RAM @ 0xffef0000
RAM mapped, Available Memory 0x07fafa00
Mapping ROM @ 0xffd00000
ROM mapped, Available Memory 0x07faf800
Mapping ROM @ 0x00000000
ROM mapped, Available Memory 0x07faf000
ttya initialized
Cpu #0 TI,TMS390Z55
Cpu #1 Nothing there
Cpu #2 Nothing there
Cpu #3 Nothing there
Probing Memory Bank #0 Nothing there
Probing Memory Bank #1 Nothing there
Probing Memory Bank #2 Nothing there
Probing Memory Bank #3 Data Access Error
ok show-devs
/TI,TMS390Z55@f,f8fffffc
/SUNW,sx@f,80000000
/eccmemctl@f,0
/virtual-memory@0,0
/memory
/obio
/iommu@f,e0000000
/openprom
/aliases
/options
/packages
/obio/power@0,a01000
/obio/auxio@0,800000
/obio/SUNW,fdtwo@0,700000
/obio/interrupt@0,400000
/obio/counter@0,300000
/obio/eeprom@0,200000
/obio/zs@0,0
/obio/zs@0,100000
/iommu@f,e0000000/sbus@f,
e0001000
/packages/obp-tftp
/packages/deblocker
/packages/disk-label
ok show-sbus
SBus slot f
SBus slot e
SBus slot 0
SBus slot 1
SBus slot 2
SBus slot 3
ok power-off
$
