so I see some code in early OF init in powerpc mac bootroms
if (something) is set, it moves a bunch of memory around, some of it endianness swapping; invalidates caches; and then enables MSR_LE|MSR_ILE (unless it's running on ppc601, in which case it sets the LE bit in HID0 for enabling little endian mode there)
it doesn't seem to touch any memory controller registers?
got a random IRQL_NOT_LESS_OR_EQUAL in ntoskrnl when playing pinball
display output is "wobbling". I reseated both ends of AV cable, still did it, happens in hbc too. noticed it only happens when GX does efb->xfb copy (inside arc firmware/nt kernel boot which writes to XFB directly everything is fine). I hope this isn't a sign of hardware failure...
based on code and documentation and hardware datasheet evidence it seems likelier and likelier that G3 macs - and only G3 macs - were to have a powerpc NT port
"It is possible to make it appear that memory is organized in little-endian format, even though it is maintained by a microprocessor that is inherently big-endian, such as the PowerPC processor. This effect is desirable, for example, when Windows NT runs on a PCI-based Power Macintosh computer, because Windows NT requires memory to appear to be little-endian."
Apple documentation : Designing PCI Cards and Drivers for Power Macintosh Computers, Revised Edition (1999-03-26), "Address Swizzling" in Appendix A.
powerpc NT was dead for two years by this point???
@wamwoowam i think it does something on a hardware level (there's code in early OF to do lots of endianness swapping then set MSR_LE|MSR_ILE if something is set), that also happens to confuse the firmware, possibly third party graphics firmware in graphics card option ROMs