1 extra cycle added when OUTing to VDP (on some cases)

By hit9918

Prophet (2923)

12-12-2014, 01:16

I guess the thing described is already done in TR emu.
But there is something different with the WAIT pin.

By Overflow

Resident (57)

15-12-2014, 10:05

Thanks guys! especially for this very interesting thread sd_natcher gives:

sd_snatcher wrote:

Quote:

I hope those 2+ dont do the 13 cycles thing in 3.57mhz mode.

That's the point, Panasonic and Sanyo ones will do, as it was proven in this thread.

As a synthesis:
Turbo R and some MSX2+, when in z80 mode, slow down IO access to VDP;
- proven by previous measurements (see this thread)
- emulated by BlueMSX (part of source given in this thread)
- also emulated by openMSX (checked by debug, see my cycle counter (explained at thread start))
- exactly 1 cycle added (checked on openMSX by debug, confirmed on real HW by own test)

Overflow wrote:

(...) my remote friend also managed to get 12 cycles on his real MSX turbo R!?!?

I was wrong, I did not undertand well, I can now confirm that this extra cycle (as slow down) is still there.

By hit9918

Prophet (2923)

16-12-2014, 17:47

Good clarification!
I wonder whether the extra cycle in z80 mode is just a side-effect of the turbo brake or whether there is another reason.

By o.geerdink

Hero (587)

16-12-2014, 18:08

It's the CIA cycle, all msx are belong to us