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Re: STE V1.5 32MHz BOOSTER - STATUS

Posted: Tue Jun 05, 2018 12:12 am
by exxos
Now with SPRRT (c) ( Super Predictive Rom Read Technology) :twisted: :twisted: :twisted: :twisted:

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Re: STE V1.5 32MHz BOOSTER - STATUS

Posted: Tue Jun 05, 2018 7:43 am
by tuxie
That looks amazing, now some stability testing ? ^^ Test with some games ? And we want Videos ^^

Re: STE V1.5 32MHz BOOSTER - STATUS

Posted: Tue Jun 05, 2018 11:54 am
by exxos
I did a video, not much to really see though.




Will leave it running throughout today and make sure the CPU can run at 40MHz...

It's possible not all CPU's may run at 40MHz so not all boosters may run at the higher speeds.

Re: STE V1.5 32MHz BOOSTER - STATUS

Posted: Thu Jun 07, 2018 3:36 pm
by exxos
40MHz as ran perfectly for several hours for about 4 days now. So the least design stable. I hope all the PLCC CPUs will run at this speed. Though ultimately, I will move to the SEC CPU like used on the STFM. Though I cannot move to that CPU without moving to a larger PLD. So it will likely be a project for next year.

Out of curiosity, I use my variable clock generator and ran at 42MHz.. For a short time.. So CPU is pushed close to its limits, but isn't actually running at its limits.. But even so 40MHz is the maximum possible stable speed. It is still faster than 32MHz anyway :)

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So I think we are about therefore final release design :)

Re: STE V1.5 32MHz BOOSTER - STATUS

Posted: Thu Jun 07, 2018 9:35 pm
by exxos
I have had a motherboard in for some time trying to figure out why boosters are unstable on it.. It is one of the more later boards with integrated blitter. I did ask around before and no one else had any problems with the boosters with this particular style of motherboard. Though this one has been a royal PITA.

I first thought there was some issue with the blitter as you was running 2% faster than normal, does not sound much, but it almost always crashed on the main blitter test. I tried delaying signals like DTACK a bit more, and it did seem to help. Though I put back the original code, and the machine was running for almost an hour without crashing.. So the fault was very intermittent but could happen anywhere in a few seconds of turning on the machine to almost an hour later, or not at all.

After scoping around, each time the scope was placed on the ROM CE signal, it instantly crashed. So there was something obviously wrong this signal somehow. I tried adding a pull-up resistor as I was thinking the load of the scope was too much for the CE line, this again did seem to work but was not conclusive, but the ROM speed dropped back down to 309% :roll: so clearly this was not direction to go in.

So I added in a series of resistor into the CE line (100R currently) and so far the machine seems stable and I can connect the scope probe now the side of the resistor without crashing. So I took some screenshots of the before and after signals...


NO RESISTOR
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100R RESISTOR
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So I think there is definitely some sort of loading or noise issue on the CE signal. I did try adding in a 22pF capacitor, but this did not change anything, so I added in a second one for 44pF and the machine did not even boot, the corrupt screen. So possible the capacitance of the GAL and ROM IC is simply too much for the STE logic to drive correctly. BOf course there looks to be approximately 1V of undershoot on the signal, could actually latch up CMOS inputs.. So I do need to read up on that again..

So I plan to make some small changes to the DUALTOS boards. Where I will run the ROM CE from the STE CE signal via a ( likely) 100R resistor. Then run the booster CE signal via a second 100R resistor. This way any interference between the GAL and ROM is reduced rather than driving them from the same resistor. Plus the overall load on the STE CE reduced considerably. So I will need to do a revised PCB (again :roll: ).


EDIT:

The ROM PDF says..
Maximum voltage is -0.6V DC, which may undershoot to -2.0V for pulses of less than 20ns. Maximum output pin voltage is VCC + 0.75V DC, which may overshoot to +7.0V for pulses of less than 20ns.
The GAL PDF says..
GAL22V10 devices are designed with an on-board charge pump to negatively bias the substrate. The negative bias is of sufficient magnitude to prevent input undershoots from causing the circuitry to latch. Additionally, outputs are designed with n-channel pullups instead of the traditional p-channel pullups to eliminate any possibility of SCR induced latching.
So the GAL are pretty hardcore by the sounds of it! So it must be the ROM having issues. Which makes sense as I had trouble getting the dualtos board on its own to run stable on this machine.

The machine under test is still running.. I have my scope sampling over each second, and undershoot max is 400mV.. So under the 600mV limit easily. So looking like another mystery solved :)

Re: STE V1.5 32MHz BOOSTER - STATUS

Posted: Fri Jun 08, 2018 4:51 pm
by exxos
STE has been on test several hours today...

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So definitely stable I think :)

Re: STE V1.5 32MHz BOOSTER - STATUS

Posted: Fri Jun 08, 2018 5:51 pm
by exxos
Now the sad news :cry: It looks like the CPU has died :cry:

I tried my other booster I made up, that one works, the booster GAL is OK and its getting the clock, but just a white screen.. So looks like 40MHz is a PLCC CPU killer :(

So I will order some likely 32MHz ones on Monday and try again... :roll:

Re: STE V1.5 32MHz BOOSTER - STATUS

Posted: Fri Jun 08, 2018 6:41 pm
by rpineau
Was it getting hot ?

Re: STE V1.5 32MHz BOOSTER - STATUS

Posted: Fri Jun 08, 2018 6:42 pm
by Atarian Computing
Aww...RIP

A moment of silence for a fallen comrade.

Re: STE V1.5 32MHz BOOSTER - STATUS

Posted: Fri Jun 08, 2018 6:54 pm
by exxos
rpineau wrote:
Fri Jun 08, 2018 6:41 pm
Was it getting hot ?
Nope, not at all.

I just unsoldered the CPU and tried in MB direct and it worked.. So big :WTF: There.. unless the heat from the heat gun "fixed it".. Doubt it...

Will plug the other booster in, and will leave that running.. but not here weekends, so likely leave running all day Monday and see if same thing happens...

I even heated this other booster CPU up with heatgun, can't touch it its burning hot and machine still running :shrug: