exxos blog - random goings on

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stephen_usher
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Re: exxos blog - random goings on

Post by stephen_usher »

The CMOS part would be slightly faster to react to a rising signal as the transition voltage between 0 and 1 is lower for CMOS and hence it would trigger at a different point. Basically the CPU would see the transition to 0 later than the NMOS part and the transition to 1 earlier by a nanosecond or so.

In other words the STE's timing only just about works by accident.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
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Re: exxos blog - random goings on

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stephen_usher wrote: Tue Nov 07, 2023 12:23 pm The CMOS part would be slightly faster to react to a rising signal as the transition voltage between 0 and 1 is lower for CMOS and hence it would trigger at a different point. Basically the CPU would see the transition to 0 later than the NMOS part and the transition to 1 earlier by a nanosecond or so.
Yeah it's all a bit of a mixed bag. It's also possibly why 2.2K pullups help with DMA issues as it changes timings by about 7ns IIRC. Though that's another oddity as why would the address and databus effect busgrant timings. Another rabbithole I am not going down. Though the pullups help with stability in particular with the HC CPU with boosters as well.
stephen_usher wrote: Tue Nov 07, 2023 12:23 pm In other words the STE's timing only just about works by accident.
Yeah that's pretty much it. Thats why its such a problem (as always) to do fixes which work across all machines. You can make or break a machine by putting a SGS or MOT CPU in the thing, or changing the ROMs. That's how bad the whole thing is. As I have always said for years, it is a miracle these things ever worked at all.

I suspect this is one of the problems I had back in the early STE booster days where only particular CPU's or GAL's would work. With fake GALs in the mix with "Random" timings to start with. Makes diagnostic very problematic. Its why I started moving away from GALs to ATF series chips as at least I had a similar starting point for timings. Getting things working across all machines I think it is going to be pretty much impossible. Things which fix one machine can then inherently break another machine.

I really did not want to go down another DMA rabbithole. I'm only doing these experiments to give people a possible solution if they have problems only when using the STE booster. Ultimately I think it can just be a plugin board because all the later boosters had the GALs in sockets. So a small plugin PCB should help solve issues should they arise again somewhere in the future. Though again unfortunately this is going to soak up a lot of my time which I don't have :(
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Re: exxos blog - random goings on

Post by stephen_usher »

Maybe adding a pull-up to the bus grant line could help (or break things further if it's the transition down to low which is the problem) then.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
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Re: exxos blog - random goings on

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stephen_usher wrote: Tue Nov 07, 2023 1:17 pm Maybe adding a pull-up to the bus grant line could help (or break things further if it's the transition down to low which is the problem) then.
I've tried a million related things already. It's why I gave up in the end and started on fixing the timings instead.
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Re: exxos blog - random goings on

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A bit neater version.

This one picks up the 8MHz after the first buffer as that is what will be on the GAL. So by the time it goes though more buffers and the GAL adding around 10ns delays, as if by magic, the 8MHz clock is still perfectly in sync 8-)

IMG_1659.JPG
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Rather problematical to find parts in stock and correct values in JLC :roll: Managed to bodge it in a way that I have 2 presets to either advance or retard the timings. It should be fine for a second test board anyway.
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Re: exxos blog - random goings on

Post by exxos »

Finally got all the MC68882 FPUs tested and accurately speed rated with my new cool stickers 8-) . They be heading to the store over the weekend.

Options will be 16MHz, 40MHz, 50MHz. All tested properly with the DFB1X accelerator.

MC68882.jpg
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Re: exxos blog - random goings on

Post by TheNameOfTheGame »

One of those things is not like the others. :lol:
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Re: exxos blog - random goings on

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TheNameOfTheGame wrote: Fri Nov 10, 2023 5:05 pm One of those things is not like the others. :lol:
Always done to annoy ;)
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Re: exxos blog - random goings on

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Where’s the tick box for the “f*caked ones?”
If it ain't broke, test it to Destruction.
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Re: exxos blog - random goings on

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PhilC wrote: Fri Nov 10, 2023 6:12 pm Where’s the tick box for the “f*caked ones?”
The bin eated all those ones.
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
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