Boosting STFM: 16MHz bus, 64MHz Shifter

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troed
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Boosting STFM: 16MHz bus, 64MHz Shifter

Post by troed » Thu Oct 05, 2017 5:05 pm

edit: A long prosaic writeup of all the steps can be found here: https://blog.troed.se/projects/atari-st ... deo-modes/


Since a few months back I've slowly been modifying one of my 1040 STFMs with the "Stefan Nitschke 16MHz mod". I got the inspiration from an Atari-Forum thread by exxos where he showed the interesting display you got if you overclocked the Shifter.

Stefan details two ways to do the mod:

16MHZ_ST.TXT.zip
(2.66 KiB) Downloaded 6 times

1) Take the 32MHz clock and feed it to the MMU instead of the regular 16MHz clock it gets from the Shifter. Use the new 16MHz output from the MMU to feed the CPU, and downclock it back to 8MHz to GLUE/therest. Also, AND the DE signal with 2MHz so that the new faster MMU doesn't feed more data to the Shifter than it can handle.

This gives you twice the RAM speed and twice the CPU speed. Not a bad boost.

2) Add a new 64MHz oscillator and feed it to the Shifter instead of its usual 32MHz. The MMU will get 32MHz from the Shifter, and then do as above - except this time don't AND 2MHz to DE. Since the Shifter is running at twice the speed it can handle MMU feeding it twice as fast.

This will give you the same RAM and CPU boost - but will also double the horisontal resolution. This is my main interest. 640*200 in 16 colors, 1280*200 in 4 and 1280*400 in mono.

IMG_20171005_111920.jpg
IMG_20171005_111920.jpg (701.17 KiB) Viewed 328 times

To do the mod I have swapped out the RAM in my machine for exxos' 4MB SIMM kit, as well as the dual fast TOS. The CPU has been swapped out for a 16MHz version. The motherboard is of a later rev with SMT versions of the MMU and GLUE.

edit: Latest status is that it's working - see page 3 of this thread.

Former latest status is that the machine boots nicely and the diagnostic cart runs through RAM and ROM tests without issues. Timer tests fail at T5 (PSG). The floppy drive is unable to read any disks - but it can itself format fine from the desktop and create a folder. Such a formatted disk can be written to by another ST, but the disk cannot be read back by the boosted machine.

Currently I'm using the 8Mhz (now 16) from the MMU to the CPU, and the 4MHz (now 8 MHz) to the GLUE/therest. Additionally I'm using a 74LS74 to downclock the 8MHz clock to 4MHz for the MFP. I'm not really sure what's causing the floppy issues since everything else seems very stable.

Bad photo, but you can see the new oscillator on the Shifter, the 74LS74 MFP clock downclock, the fast TOS etc. Also my logic analyzer which I used to verify that the 4MHz clock indeed works ...
Attachments
IMG_20171005_142547.jpg
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Last edited by troed on Thu Oct 12, 2017 2:18 pm, edited 2 times in total.

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

Post by exxos » Thu Oct 05, 2017 5:50 pm

Fantastic stuff :bravo:

I really hope we can get this running stable, if you can iron out all the bugs and make it into something worthwhile than we can gain of course extra speed and extra resolutions which can be integrated into future boosters and even the new motherboard :)

I did not really make many notes about this, but the post I did on my site is below.

http://www.exxoshost.co.uk/atari/last/1 ... JULY192016

I only had the original gem bench back then, was not really accurate, some really looking forward to seeing GB6 results. They probably will not differ much from 200% across the figures anyway.

I was running stable enough to run gem bench back then, but overall it was not totally stable. There is a lot of clock skew which I believe is causing the issues. To correct this basically thought about using something like a binary counter as a clock dividing circuit. So then you start off with a 64 MHz from the oscillator and clocking down to 32MHz, 16MHz, 8MHz, 4MHz, 2MHz.

Though as the output from the oscillator is a little weak, it may ultimately be worth trying to start off with 128 MHz as the master clock, then at least 64 MHz will be buffered along with all the others. That these speeds could be pushing basic logic chips past their limits.

I need to really check, the binary counter needs to adjust every output at the same time. The basic problem with clock dividers using flip-flops is every flip-flop adds propagation delay, and the more change of flip-flops the more the delay and the more the clock skew is. This would not be a good thing. I will ultimately I think replacing all the clocks will solve a lot of the stable of the issues. Most of the clocks are cut anyway so buffering them should not be a problem.


EDIT:
Actually just found this page is used when explaining this..

http://www.electronics-tutorials.ws/cou ... unt_3.html


So the 74F161 seems the best candidate for clock buffering.

http://www.tij.co.jp/jp/lit/ds/sdfs056b/sdfs056b.pdf
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troed
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Re: Boosting STFM: 16MHz bus, 64MHz Shifter

Post by troed » Thu Oct 05, 2017 7:45 pm

Here's a capture of the 16MHz (from MMU), 8MHz (from MMU) and 4MHz (divided by the 74LS74 from the 8MHz) taken at the maximum speed of my LA. The relationship between the clocks is stable between captures at that speed.

la_16_8_4_400mhz.png
la_16_8_4_400mhz.png (106.11 KiB) Viewed 301 times

edit: Annotated. I'd say the 8MHz clock (MMU original 4MHz) is lead, ~2ns ahead of the 16MHz (original 8MHz). The new MFP clock is ~15ns behind the 8MHz.

la_16_8_4_400mhz_annotated.png
la_16_8_4_400mhz_annotated.png (61.15 KiB) Viewed 300 times

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

Post by exxos » Thu Oct 05, 2017 9:33 pm

troed wrote:
Thu Oct 05, 2017 7:45 pm

edit: Annotated. I'd say the 8MHz clock (MMU original 4MHz) is lead, ~2ns ahead of the 16MHz (original 8MHz). The new MFP clock is ~15ns behind the 8MHz.
You *should* be ok with those timings... never know with this stuff though.

You also need to post scope images to see the ringing on the signals and adjust series resistors accordingly.
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Re: Boosting STFM: 16MHz bus, 64MHz Shifter

Post by troed » Thu Oct 05, 2017 9:39 pm

exxos wrote:
Thu Oct 05, 2017 9:33 pm
You also need to post scope images to see the ringing on the signals and adjust series resistors accordingly.
Yeah apparently I need an oscilloscope extension for my LA and it's only available for the previous hw version :( Or something. I had really hoped not having to buy a separate oscilloscope as well ...

But, let's start with changing the address/data bus resistor packs and break open that fresh refurbished Epson 340 tomorrow ... :)

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

Post by exxos » Thu Oct 05, 2017 9:43 pm

troed wrote:
Thu Oct 05, 2017 9:39 pm
Yeah apparently I need an oscilloscope extension for my LA and it's only available for the previous hw version :( Or something. I had really hoped not having to buy a separate oscilloscope as well ...
ah ok, thought you had a scope (my bad sorry!)
troed wrote:
Thu Oct 05, 2017 9:39 pm
But, let's start with changing the address/data bus resistor packs and break open that fresh refurbished Epson 340 tomorrow ... :)
Yes, 16mhz is unstable with my boosters without 2.2K. So once you have done that, fingers crossed that your machine starts to behave better!

I would make sure you have some 33R in series with clock inputs and outputs. The LA does not show the "real picture" a lot of the time. Signals could be glitching like mad, and just because the LA does not see them, doesn't mean that the ST chips won't see them either ;)
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Re: Boosting STFM: 16MHz bus, 64MHz Shifter

Post by troed » Thu Oct 05, 2017 9:47 pm

exxos wrote:
Thu Oct 05, 2017 9:43 pm
ah ok, thought you had a scope (my bad sorry!)
I thought so too until I checked what was in the LA box I purchased a while ago today ;)
I would make sure you have some 33R in series with clock inputs and outputs. The LA does not show the "real picture" a lot of the time. Signals could be glitching like mad, and just because the LA does not see them, doesn't mean that the ST chips won't see them either ;)
Yeah, currently I have none :)

With that said, the GLUE should really trip up noticeable by just looking at the screen if it saw false clock glitches I think. But I have a bunch of 33R waiting right next to the computer already so ... :)

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

Post by exxos » Thu Oct 05, 2017 9:53 pm

troed wrote:
Thu Oct 05, 2017 9:47 pm
With that said, the GLUE should really trip up noticeable by just looking at the screen if it saw false clock glitches I think. But I have a bunch of 33R waiting right next to the computer already so ... :)
GLUE is the chip which causes hell with DMA stuff for some odd reason, IE floppy drive. If something is slightly wrong, it mostly shows on floppy access more than anything. I have lost much time fighting with the GLUE :roll:

Your having fun though, thats all that matters ;)
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Re: Boosting STFM: 16MHz bus, 64MHz Shifter

Post by troed » Fri Oct 06, 2017 11:08 am

Pullups changed on address and data bus, no change.

Tested with the freshly refurbished Epson 340, no change.

However, since I did a bit more testing:

The drive seems to have issues reading more than writing/formatting. Most often it will simply believe disks have 0 bytes used in 0 files, but sometimes it shows some of the data. Pressing ESC for a re-read of the directory content will show something else, etc. Like:

1 files
ESC
13 files
ESC
10 files
ESC
18 files

... so to me this really looks like something to do with the transfer of data through the floppy controller, but I don't know.

When I find time to work on it again I'll add some 33R to the clocks. After that I don't really know .. maybe see if the LA can give some insight specifically around floppy/DMA clock and data.

/Troed

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

Post by exxos » Fri Oct 06, 2017 12:45 pm

Add a 1K resistor (pull up) on CPU /DTACK and /AS see if that helps. Also add a sil array on the DMA databus.
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.
https://ataristeven.exxoshost.co.uk/Steem.htm Latest Steem Emulator

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