have tracked down a weird CPU bug: if i do a soft reboot from within SETUP with CTRL-SETUP (a key combination from the the manual) the Z80 corrupts the 808x address space with stack data.
What i found out:
* BIOS begins an extensive memory test (BITTEST_AX) -https://github.com/shattered/retro-bios/...-022e5-00#L3931
* problem gets visible at this location:https://github.com/shattered/retro-bios/...-022e5-00#L4175
- BX is current address
- AL contains XOR result of correct and actual value
Z80 writes to $07f0/$07f1 (reflected at 808x offset $87f0/$87f1).RESULT: ERROR 19
Main Board RAM (0-64K)
Why does the Z80 interfere with the memory test?There is a reasonable suspicion the ZFLIP flag is set or handled wrongly. I just cant find where...
P.S.: floppy test on the DIAG.DISK (from 'indiviual tests') now aborts with a 'Z80 response error'. Coincidence?
Any ideas? :-)
Screenshot of Z80 caught in the act:https://dl.dropboxusercontent.com/u/37819653/BANNISTER/Z80_writes_to_8088_memory.jpg