Open source 14MHz 68000 accelerator

[Glen M]

Originally Posted by Mathesar

Great video and I am glad you like the card!
Your comment about it being the perfect Dread accelerator made me smile. It could have been back in the day right? Sold as a bundle? I would have certainly wanted it for Sinterklaas back then!

That exactly what I was thinking, I could see it flying off the shelves back in the day.

Originally Posted by Mathesar

Spot on Somewhere along the project I had the idea to do some tricks with the address lines to relocate the trapdoor RAM to $D00000. This way the trapdoor RAM would be added to the system memory instead of overruled. This would give you 1.5MB of ranger RAM of which only the first 1MB would be really fast. It costed too much logic though.

Thanks for the further information, I'll see about putting a pinned comment to the top of the video explaining this.

Originally Posted by Mathesar

I hear varying reports about compatbility with the IDE68K.
It works fine though with the trap door chip ram mod. (I did the same )

I can only try the IDE68K and glad to hear the trap door chip ram mod will work. I'll let you know how I get on.

[sparx]

Originally Posted by Glen M

I released a video on this card yesterday. There are a fair few comments from people asking were to get one, I don't suppose anyone is building them at present or knows of someone who is?

One other question that's getting asked is, why is the fast ram mapped to the slow ram address space?

I don't suppose anyone could provide an answer to this and using small words so I can understand lol.

Howdy mate

I have 2 left over that I'm just about to list on eBay

Great vid btw!

[Glen M]

I was toying with a 68010 in the accelerator yesterday but its hideously unstable. I think the problem is the chip itself just doesn't like the 14mhz clock but just wanted to ask in here if there would be any reason on the accelerator for instability with that chip compared to the 68k itself.

Its unstable in so much as software will load but quickly crash, either throwing a guru or just straight black screen. Seems to run stable for approximately 1 minute. I've noticed the chip gets hot, considerably hotter than the 68k so my best guess is that this refinished chip out of china is a slow part being pushed well beyond its spec. I don't think its a 12mhz chip as inscribed on the top of it.

[breech]

Yep I would say you are right, probably a rebadged 8 or 10mhz part. Try a ceramic 12.5mhz MC68010L10, they are less likely to be molestered. Adding heatsinks will extend the life of the chips.

[nikosidis]

@Glen M

I can tell you that the cards are rock stable when they are working.
I have no problems like you mention.

[Glen M]

Thanks, that's what I thought myself but just mentioning it in case I was missing something obvious.

[Mathesar]

I have also tried a 68010 labeled as MC68010FN12 without problems. One of the things to check with these cards though is the voltage on J2/14MHz. If the voltage differs too much from 2.5V the clock signal might not be too good for an overclocked CPU.

And yes, these 68010's, not being HCMOS, do run hot

[Glen M]

Originally Posted by Mathesar

I have also tried a 68010 labeled as MC68010FN12 without problems. One of the things to check with these cards though is the voltage on J2/14MHz. If the voltage differs too much from 2.5V the clock signal might not be too good for an overclocked CPU.

And yes, these 68010's, not being HCMOS, do run hot

Do you mean on JP2? Its sitting at 3.7volts on my card.

Regardless though its rock solid with the 68k processor.

[sparx]

Originally Posted by Glen M

Do you mean on JP2? Its sitting at 3.7volts on my card.

Regardless though its rock solid with the 68k processor.

J2, also labelled 14MHz - it's located near the 68000

[Glen M]

Found it, its 2.3v. 5v reads as 4.93 on my machine so half that would be 2.46. Not that far off really. I don't think the issue is with the card though, its more likely to be the processor.

[pandy71]

Originally Posted by Glen M

Found it, its 2.3v. 5v reads as 4.93 on my machine so half that would be 2.46. Not that far off really. I don't think the issue is with the card though, its more likely to be the processor.

You may try to slightly increase power voltage and provide good cooling - something like small heatsink+fan solution from notebooks or graphic cards.

[Mathesar]

Originally Posted by Glen M

Found it, its 2.3v. 5v reads as 4.93 on my machine so half that would be 2.46. Not that far off really. I don't think the issue is with the card though, its more likely to be the processor.

That's a good value giving you a clock duty cycle of about 47%.
Yes, I think the issue is with the processor chip.

[nikosidis]

I made my own design of the card

https://ibb.co/VJrpyYB

Love the card.

Even Sensible world of soccer benefit from it.
Without the accelerator there are a few slowdowns. With it it is not a single slowdown

[Mathesar]

I have the schematics done for a slightly upgraded version. It fixes the A590 compatibility issue by having tristate logic on the ~AS signal. I am thinking of doing this version as aN accelerator / clock doubled only version with a fast local slot on which some fastram can later be added. This fastram could then even be some autoconfig ram instead of ranger ram.

What do you think? Nice? DIP64 or PLCC CPU?

Also, what about some harddisk option? I have this idea of a super simple simple, semi bit banging SPI interface for an SD card. Not autobooting of course.. But how much of a problem is it to boot from a bootfloppy?

[hooverphonique]

Originally Posted by Mathesar

I am thinking of doing this version as aN accelerator / clock doubled only version

Is the current version not exactly this already?

Originally Posted by Mathesar

What do you think? Nice? DIP64 or PLCC CPU?

The PLCC version is easier to find as 14MHz compatible, isn't it?

[nikosidis]

Originally Posted by Mathesar

I have the schematics done for a slightly upgraded version. It fixes the A590 compatibility issue by having tristate logic on the ~AS signal. I am thinking of doing this version as aN accelerator / clock doubled only version with a fast local slot on which some fastram can later be added. This fastram could then even be some autoconfig ram instead of ranger ram.

What do you think? Nice? DIP64 or PLCC CPU?

Also, what about some harddisk option? I have this idea of a super simple simple, semi bit banging SPI interface for an SD card. Not autobooting of course.. But how much of a problem is it to boot from a bootfloppy?

That sounds fantastic Mathesar
I like PLCC CPU.
SD card is perfect. Why will Amiga not boot from it?

[Mathesar]

Originally Posted by nikosidis

That sounds fantastic Mathesar
I like PLCC CPU.
SD card is perfect. Why will Amiga not boot from it?

Because it will not act like a gayle-like IDE interface but something else. I am looking at building something in the style of the current design, so with a minimum number of discrete logic chips. And that will require a custom driver that needs to be loaded from a floppy. However, that floppy will only have to load the driver and hand over the boot process to the boot partition on the SD card. I have something similar running on my A500 and the boot delay is very minimal.

[nikosidis]

Originally Posted by Mathesar

Because it will not act like a gayle-like IDE interface but something else. I am looking at building something in the style of the current design, so with a minimum number of discrete logic chips. And that will require a custom driver that needs to be loaded from a floppy. However, that floppy will only have to load the driver and hand over the boot process to the boot partition on the SD card. I have something similar running on my A500 and the boot delay is very minimal.

Ok, that sounds good. I guess when loaded you can reset without loading the driver again.

What about doing a custom Amiga Rom with the driver in it?

It is this programable eprom Amiga Rom to buy now where it is possible to select roms.

[PeteAU]

Originally Posted by Mathesar

I have the schematics done for a slightly upgraded version. It fixes the A590 compatibility issue by having tristate logic on the ~AS signal. I am thinking of doing this version as aN accelerator / clock doubled only version with a fast local slot on which some fastram can later be added. This fastram could then even be some autoconfig ram instead of ranger ram.

What do you think? Nice? DIP64 or PLCC CPU?

Also, what about some harddisk option? I have this idea of a super simple simple, semi bit banging SPI interface for an SD card. Not autobooting of course.. But how much of a problem is it to boot from a bootfloppy?

Do you mean to remove the SRAMs and have a separate board for memory? The fastram in ranger-space was very novel and cute solution, but these are also interesting ideas.

How would you do DRAM and keep it typically Mathesar retro? GAL20v8?

I had this idea of 3 optional boards: 14mhz accel, ram board, ide board. All connected together via 2x32 (64-pin) right-angle header. So you could keep expanding things to the right-hand side without stacking on top.

Bootfloppy from a gotek is not really painful, I reckon.

P.S. What would be the difficulty in clocking the PLCC 68000 at 21 MHz? Heaps more logic?

[Mathesar]

Originally Posted by PeteAU

Do you mean to remove the SRAMs and have a separate board for memory? The fastram in ranger-space was very novel and cute solution, but these are also interesting ideas.

How would you do DRAM and keep it typically Mathesar retro? GAL20v8?

I had this idea of 3 optional boards: 14mhz accel, ram board, ide board. All connected together via 2x32 (64-pin) right-angle header. So you could keep expanding things to the right-hand side without stacking on top.

Bootfloppy from a gotek is not really painful, I reckon.

P.S. What would be the difficulty in clocking the PLCC 68000 at 21 MHz? Heaps more logic?

You had the same idea that I had . Yes, the idea was to separate the accelerator and ram boards. And yes, the plan is to have connectors on the side... This way I can develop in phases, first a DMA compatible 14MHz cpu (maybe with SD interface), then a fast ram board. Maybe we could indeed do a dram board. I think autoconfig is also doable with just discrete logic.... No GAL's needed. I never looked into a 21MHz version but the biggest problem would probably be the E clock.