Boosting STFM: 16MHz bus, 64MHz Shifter

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troed
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Re: Boosting STFM: 16MHz bus, 64MHz Shifter

Post by troed » Fri Oct 13, 2017 8:12 pm

exxos wrote:
Fri Oct 13, 2017 8:04 pm
Fantastic to finally see a proper speed result! Would also be nice to see stock medium res benchmarks at some point ;) I got 200% pretty much across all tests with GB3, but it wasn't a good test... Probably not far out from your second image anyway...
BTW, it seems GEMbench cannot save screenshots in "low" res ... ;) (Greyed out)
exxos wrote:
Fri Oct 13, 2017 3:27 pm
Thinking out loud here...

Could we not re-generate the syncs and rebuild a higher vertical resolution ? We have control over DE but if we could double the vertical sync speed as well..

Maybe no reason to start the frame earlier and gain a few extra pixels in the borders as well ?
We can't do anything about GLUE and its counting of lines - but we have full control over DE. It's trivial to do the good old overscan hw mod of course, but it might be possible with some fast logic to selectively add a few lines before and after the regular screen. I think 640x240 and 1280x480 would be nice and fully doable.

It would be a slight nightmare to sync this _exactly_ to the line start and line end of the GLUE-controlled lines though.

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Re: Boosting STFM: 16MHz bus, 64MHz Shifter

Post by exxos » Fri Oct 13, 2017 8:18 pm

troed wrote:
Fri Oct 13, 2017 8:12 pm
BTW, it seems GEMbench cannot save screenshots in "low" res ... ;) (Greyed out)
Yeah, GB6 does not run in low res :) obviously different screen detection routine there, damn my lazy coding ;)

troed wrote:
Fri Oct 13, 2017 8:12 pm
We can't do anything about GLUE and its counting of lines - but we have full control over DE. It's trivial to do the good old overscan hw mod of course, but it might be possible with some fast logic to selectively add a few lines before and after the regular screen. I think 640x240 and 1280x480 would be nice and fully doable.

It would be a slight nightmare to sync this _exactly_ to the line start and line end of the GLUE-controlled lines though.
What I mean is not letting the GLUE do any of the counting at all..generating new sync external to glue can be done. though I don't know if generating syncs externally would break other stuff.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

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troed
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Re: Boosting STFM: 16MHz bus, 64MHz Shifter

Post by troed » Fri Oct 13, 2017 9:53 pm

troed wrote:
Thu Oct 12, 2017 10:55 pm
Alright, so here's the first slightly negative observation. The Shifter is indeed getting extremely stressed when in monochrome (where its internal pixel clock is the highest). I didn't see this until now, it takes a few minutes to appear and I've been mostly playing around in "low" res. Also, it's dependent on the actual graphics shown - something I've seen with regards to Shifter behaviour in my sync scroll/overscan research on regular machines as well.
After some more testing, this is indeed caused by Shifter timings being borderline. I had this, quite severe, where it then suddenly "popped" into banded state (every fifth word black, i.e, black vertical columns) where it otherwise was fine, and then it "popped" into a non-banded state again (but with wrap-around at left side) again otherwise displaying everything nicely.

So, it's not a general case of the Shifter not being able to handle the high(est) pixel clock but being down to very delicate borderline timing. This is good - might be something that can be tweakable for each installation or so.

/Troed

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exxos
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Re: Boosting STFM: 16MHz bus, 64MHz Shifter

Post by exxos » Fri Oct 13, 2017 10:35 pm

troed wrote:
Fri Oct 13, 2017 9:53 pm
After some more testing, this is indeed caused by Shifter timings being borderline. I had this, quite severe, where it then suddenly "popped" into banded state (every fifth word black, i.e, black vertical columns) where it otherwise was fine, and then it "popped" into a non-banded state again (but with wrap-around at left side) again otherwise displaying everything nicely.

So, it's not a general case of the Shifter not being able to handle the high(est) pixel clock but being down to very delicate borderline timing. This is good - might be something that can be tweakable for each installation or so.
From my testing before, if the video was shifting 16pixels to the right and "wrapping around" it was the GLUE clock having to much delay.

Even so, random faults like this may just be noise on some signal. Its common and can get time consuming to track down. Leave all the fine tuning to me when I catch up with stuff and can get it all in my V2.6 prototype :)
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
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troed
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Re: Boosting STFM: 16MHz bus, 64MHz Shifter

Post by troed » Sun Oct 15, 2017 7:46 pm

I just realized I don't need to guess about the difference between using the F161 16MHz clock for CPU (where memory only reached 100% speed) and using the MMU 16MHz clock (where memory access got to 200%) - I could use the LA to see what the difference is :P

clocks_mmu_or_f161.png
clocks_mmu_or_f161.png (134.28 KiB) Viewed 269 times

Surprising, actually.

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Re: Boosting STFM: 16MHz bus, 64MHz Shifter

Post by exxos » Sun Oct 15, 2017 9:57 pm

These are my scope readings I took on a stock machine ages ago...


8MHz - 32MHz
8_32.png
8_32.png (4.55 KiB) Viewed 260 times

16MHz - 32MHz
16_32.png
16_32.png (4.54 KiB) Viewed 260 times

8MHz - 16MHz.
8_16.png
8_16.png (4.63 KiB) Viewed 260 times

They are all perfectly in sync.

You're 161 16MHz line is out of sync with the rest of the system. I still think that is covering up a sync issue with DTACK on the rest of the system. IE delaying the clock to the CPU so it reads DTACK later.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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