Sorry for the delayed response. I haven't browsed this forum very thoroughly for a while.
Could it be that the PPC Macs have wider ROMs than what you expect and interleave differently thus producing confusing results? On the IIci, I have recently confirmed with your experience that they are 8-bit and interleaved 1 byte at a time amongst 4 ROM chips. But a while ago when I interleaved the PEX FLASH ROM together, each flash chip was actually 32-bit, so I took 4 bytes from #1, 4 bytes from #2, 4 bytes from #1, 4 bytes from #2, etc. This may have nothing to do with the PEX ROM SIMM however.
It doesn't answer your question, but in my Mac ROM Verify hack that I posted somewhere, I have noticed that doing a checksum on a PPC ROM pulled via GetRom does work if you use only the first 3 MB of 4MB ROMs. This could be dumped from an internal 68k emulator or something and not the actual ROM however because GetROM is presumably a 68k app and thus is running in some sort of emulation mode.
More clues though:
All dumps that I've made on PPCs are always different on different PPC Macs. None are identical like you might expect if this is some "emulation" ROM.
All dumps I've made contain the appropriate startup sound(s), including the TAM.
All dumps that I've made match checksums with those found at various places online.
There's no answer in what I mentioned, but maybe there are helpful clues.
Could it be that the PPC Macs have wider ROMs than what you expect and interleave differently thus producing confusing results? On the IIci, I have recently confirmed with your experience that they are 8-bit and interleaved 1 byte at a time amongst 4 ROM chips. But a while ago when I interleaved the PEX FLASH ROM together, each flash chip was actually 32-bit, so I took 4 bytes from #1, 4 bytes from #2, 4 bytes from #1, 4 bytes from #2, etc. This may have nothing to do with the PEX ROM SIMM however.
It doesn't answer your question, but in my Mac ROM Verify hack that I posted somewhere, I have noticed that doing a checksum on a PPC ROM pulled via GetRom does work if you use only the first 3 MB of 4MB ROMs. This could be dumped from an internal 68k emulator or something and not the actual ROM however because GetROM is presumably a 68k app and thus is running in some sort of emulation mode.
More clues though:
All dumps that I've made on PPCs are always different on different PPC Macs. None are identical like you might expect if this is some "emulation" ROM.
All dumps I've made contain the appropriate startup sound(s), including the TAM.
All dumps that I've made match checksums with those found at various places online.
There's no answer in what I mentioned, but maybe there are helpful clues.