CURRENT PROTOTYPE STATUS (SEC 64MHz 68000)

[exxos]

This project is basically on hold when I figure out some stuff..

I needed a flexible register to store settings.. I was thinking of using a ATtiny where Urban said he could do the firmware this.. Basically using the tiny as some simple flash storage.. But I've been thinking over the past few days that really I should be moving over to the RTC chip as it has built-in NVRAM where I can store some settings and of course it gives a clock as well.

I may have mentioned the technicals of such a thing before. Basically things like TOS 104 / 206 select would be software switchable stored in a simple flash register so that once it is set, it will stay like that without having to load software to program or set things each time.

So rather than spending time on the tiny chip, I have been talking to Icky about doing a small development board to work on the flash and RTC stuff. It would make more sense to figure this stuff out and programmed the software for it before going any further with the SEC booster...

So this project has now branched to the topic below.

https://www.exxosforum.co.uk/forum/viewt ... =73&t=1697

[exxos]

The "full" version of the SEC booster with flash and RTC & fast-ram I am just not going to go ahead with this project anytime soon. As said above, there is much work to be done with the RTC & Flash firmware yet which are own projects in their own right which will take a lot of time.

As the "simple" SEC is basically completed. When/If I get chance I will produce a few of those boards as the SEC design will move over to the remake project ultimately, so it needs more testing before that happens anyway.

Overall I am trying to reduce the workload on projects to concentrate on the remake boards.

[exxos]

As my SEC machine was hijacked for testing the V2.3 booster, I just put it all back together and the blitter was seriously freaking out! It would basically crash getting to desktop and then totally corrupt the screen with garbage.

Turns out, when I added in the 390pF capacitor back onto A1, I soldered it directly onto the ROM board. Originally I had a yellow wire connecting the capacitor to the outer GND part of the motherboard is shown in the image below..

So I put the wire back in, and the blitter is now behaving! Totally bonkers!

I think there's a little more investigating to do circulating around A1 in relating to the DMA & BLITTER!

On the next revision board I have rooted A1 via the PLD in case that would help with something at some point.

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[exxos]

Scope came out..

Left to right..

A1 as stock.... A1 with 390pF added... A1 with wire and 390pF added... Only the last image works...

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I'm going to try adding a few ohms to see what happens... I suspect there needs to be a delay on A1 for some reason

EDIT:
68R in series didn't work at all again...

[exxos]

I measured A1 on the DMA pin directly and saw total chaos..But this actually works oddly.

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Without the capacitor there is reasonable nice square wave..

So I cut the A1 line at the DMA and added about 100R series with it. This did not allow the machine to boot (which is what happens without the capacitor).

Then I added 50pF onto it and now the machine boots perfectly and the waveform looks pretty nice as well.

Oddly with just the 50pF on its own, machine does not reset, but about 30 seconds later it does and then works perfectly.. Bizarre..

I don't think this is a bad signal on A1, but it just must need a tiny delay there some reason.

I did try keeping BGACK low for one extra cycle in case the CPU was starting the next cycle too fast after a DMA cycle (or blitters) but this did not make any difference.

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[exxos]

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This scope shows A1 before and after the resistor.

The yellow signal is after..

I was seeing some undershoot and overshoot earlier this was smoothed out by the resistor and capacitor.. So it is cleaning up the signal. I have zoomed in and checked a lot between the two, and I do not really see any delays there. As you can see in the image above, signals still look pretty much identical. But without the resistor and capacitor, machine does not boot up at all.. So it's a bit of a mystery still..

[exxos]

SEC_F3.jpg (73.27 KiB) Viewed 4406 times

So thanks to a generous person of sending me these boards... I will bag a few of these up to send off for assembly... This board of course has the sound fix as mentioned previously, and also I have A1 routed via the PLD to experiment with that issue a little more...These are running at 50MHz..

Benchmarks https://www.exxosforum.co.uk/forum/viewt ... =42&t=1834

Small number of these boards when madeup and tested will be available in my store as beta test versions..

[exxos]

I only had 3 ATF1508 chips here, so ordered seven more (at £10+ a pop they not cheap!) , they should be here today. I have packed up enough parts to send off for 10 to be made, likely seven will make it to my store.. Bank holiday weekend will delay things as will be able to post them off until next week now


This is the video of it in action in case anyone missed it

[exxos]

Got my boards back

Probably be another month before I can invest some time into them though

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[Icky]

Nice! Looking good.