#534 VRAM corruption even with too_fast_vram_access=ignore

Next_release
closed-fixed
5
2014-10-01
2014-05-19
SD Snatcher
No

VRAM data is getting corrupted even after enabling the too_fast_vram_access feature.

Steps to reproduce the problem:

1) Boot a Sanyo PHC-70FD
2) Load the game Elite, disk version
3) Type the following commands on the console:

set z80_freq 80000000
set too_fast_vram_access ignore
set z80_freq_locked off

The screen will get corrupted data everywhere.
Note: The Z80 frequency is 80MHz, not 8Mhz

The corruption only stops if I also enable the "set cmdtiming broken" command. But that doesn't make sense, as this is a MSX1 game and the blitter isn't used.

For the turbofixing use case, I need to also test the scenario where the CPU is at high speed, but the blitter is still at the standard speed.

Curiously enough, the test has exactly the same results on a National FS-1300 (+ Sony HB-F1 drive), but this is a MSX1 computer with the TMS9918 VDP and without any blitter. (be sure to release the z80_freq_locked with this floppy interface only after the game is already loaded)

Tested with openMSX 0.10.1 on Mac OS-X 10.9.2.

Discussion

  • In some cases, this means the workaround for #471 isn't effective.

     
  • Fixed by wouter in commit 3ab96c51ef0cff07c7dfb3c2c294e7e4c45c88dd
    Thanks!

     
    • status: open --> closed-fixed
     
    • assigned_to: Wouter Vermaelen