"Clue" has garbled green text when selecting difficulty

[Former user]

Original issue 318 created by csatech31 on 2013-01-19T03:01:23.000Z:

What steps will reproduce the problem?
load rom, when selecting difficulty, there are green garbled letters on screen making it a bit hard to read

What is the expected output? What do you see instead?
able to select difficulty with no problems

What version of the emulator are you using (official, SVN revision,...)?
1.7.3 SVN r757

[Former user]

Comment # 1 originally posted by ekeeke31 on 2013-01-19T10:06:06.000Z:

Indeed, i never noticed this before so i am not sure if this was introduced recently or was always the case (if you could test it with old releases, this could help).

It does not happen when the console is started in PAL mode which seems to indicate an issue with VBLANK timings (probably DMA during VBLANK), I will investigate it.

[Former user]

Comment # 2 originally posted by ekeeke31 on 2013-02-21T20:14:52.000Z:

for the record, it is caused by a VRAM cleanup operations being interrupted by vdp interrupt, which cause all later VRAM writes to be ignored after the interrupt callback returns

depending on when the VRAM write operation was initiated in the frame you got more or less garbage on screen.
the problem is that the game is kinda bugged and works on real hardware by luck, because it does not sync itself with anything related to vdp before starting the operation, so having instructions or memory access timings just a bit off or delayed can cause the issue to appear or disappear, which is why it doesn't happen the same in all emulators

i can make it work by hacking the timings but i would prefer not and instead find what is off or delayed in the emulator and what 100% accurate timings should be

[Former user]

Comment # 3 originally posted by ekeeke31 on 2013-02-22T22:44:28.000Z:

Took me some time but it was actually fixed by handling FIFO timings properly in the case of invalid write access.

fixed in r762