Re: [hatari-devel] looking for someone with a mono monitor

Am 28.11.16 14:37, schrieb Troed Sångberg:

Hello Troed,

thanks for your answer and sorry for my again very late answer, it is difficult for me to spend time on this matter that I though like a lot.
At first a thank to Thomas Huth for pointing me to that great presentation of yours on youtube. I didn't know you even "reverse engineered" the state machine of the Glue-Chip, very amazing to learn all those details! Especially the part with the "wake-states" indeed enlightens me.

However! What you just described above sound amazing - and would be the first time external sync (oh how much I tried doing tricks with it in color in the good old days .. ) has been used for any sync trick - and a proper _split screen_ at that is incredible! I need to think about this for a while - my naïve first guess would be that you manage to skip the actual vsync pulse but not the reset-vbase that happens during the vsync phase. If so then there's an 800 lines long 30.5Hz frame being displayed which would be very much non-sync-clean ... but I'll have to look into it.

[...]

This, like Thomas said, is surely all about wakestates. The fact that it did work on both short and long top-border GLUEs should mean it works on all STFs. STEs would need verification. For your info, the GLUE and MMU can be offset 0-3 cycles selected "at random" (but with huge machine dependent attractors) at cold boot. This affects when you from the CPU need to poke your values into the freq and res registers - see this wiki page for my documentation of this phenomena: http://www.atari-wiki.com/index.php/ST_STE_Scanlines

Hmm, maybe my explanations were confusing. The part about only 2 of 7 STs and those 2 were "13 line" and "29 line" Glues referred to my experiments with internal and external synchronization. So only on 2 of 7 STs I was able to trigger a second VBL-phase with that trick, the other 5 STs just showed black colour on the respective lines but still increased the video-count as usual (no line skippping or such).
It still astounded me that a "13 line Glue" and a "29 line Glue" both initiated a "2nd VBL" with the Ext/Int-Synch trick since I considered those two Glues must definitely be from separate production lines (I heart that rather older Glue-Chips only have 13 lines in the upper border for 50 Hz and that this was "corrected" later somehow). Opening the right border in monochrom always worked on all STs.

If you ever feel like coding again, I've published a one line wakestate-detection routine that tells you which ST wakestate (or if it's an STE) you're currently in, by manipulating the GLUE and checking the results.

Sigh, I really would love to play with that stuff again. The first challenge would be to find and set up my old Atari ST again from our attic.

was, that the spot where you have to open the right border in monochrome depended on moon wetness, weather situation, whatsoever .... it was different any time I turned on my ST. So I had to "extend" the time I switched to colour mode to make sure the "critical spot" was within that time, hence I had to stay in colour mode for more than 24 cycles (would have to look into the source to see for how long).

The shortest switch I know how to do is 4 cycles long, 16 pixels in mono, and if you know which wakestate you're in you don't need better accuracy than that (actually 1 cycle would do, but I know of no way to do such a switch back'n'forth).

Hmm, should try that. Anyways, those days I was a little "jealous" at the color mode since they're able to continuously display their line and open the right border and I will always have this black gap there.

Regards,

Starbug