Open source 14MHz 68000 accelerator

[nikosidis]

Originally Posted by Mathesar

I brought my A500 to a local retro computerclub some time ago with the accelerator installed. It was running the free demo of Dread. While I was chatting with someone two guys started playing Dread and commented to each other how smooth it runs a bog standard A500. I didn't ruin it for them...

Haha, that is a funny story Dread on standard A500 is ok, but with this accelerator it is perfect!



Your accelerator is a true joy to use. With many games made for Scorpion Engine they usually require something like A1200 CPU specs. so there you have it

[erikarn]

I'll go next test it on the diagrom.

I wonder if the E clock is "ok enough" here? hm

[Mathesar]

Originally Posted by erikarn

I'll go next test it on the diagrom.

I wonder if the E clock is "ok enough" here? hm

It's E clock vs VPA/VMA. The info is further back in this thread. But give diagrom a try. For me it was a life saver!

[erikarn]

Originally Posted by Mathesar

Yes, U5A pin 6 should still go to U5B pin 13. So it is indeed best to cut /AS7 at the plug header.

Yes indeed! That's the plan!

Originally Posted by Mathesar

It's E clock vs VPA/VMA. The info is further back in this thread. But give diagrom a try. For me it was a life saver!

Yeh I'm still trying to find it; and it may be a rev5 one which means I have to do some surgery. I'll let you know soon.

[erikarn]

ok, it boots fine into diagrom, and all the tests pass.

if i remove the dual uart board, it stops booting to yellow screen, it boots to 2.04 screen, but doesn't see or try to boot from the SCSI card ROM.

i booted a 1.3 workbench disk and ran amigatestkit; all fine there too.

hm, wonder what's going on! anything else to try?

[erikarn]

(and yes, the CIA tests all pass, both diagrom and atk)

[erikarn]

hm, i wonder if the timing between it and buster on the a2000 is slightly whack?

[Mathesar]

Hmmm, I don't know the A2000 well enough to comment. You did do the DMA hacks? In any case you could try to boot without the ranger/fast RAM?

[erikarn]

Yeah, DMA hacks were done. It shouldn't need the DMA hacks just to poke the autoconfig ranges.

I'm gonna go find/use my salae and see if i can capture some clock phase / buster timing snapshots.

[erikarn]

here's some traces during autoconfig in diagrom! all done in pulseview.

[erikarn]

here's another trace.

what's going on between as7/dtack7 and as14/dtack14?

[Mathesar]

Originally Posted by erikarn

here's another trace.

what's going on between as7/dtack7 and as14/dtack14?

AS7 is a delayed version of AS14.
Dtack7 is sampled at the falling edge of the 7mhz clock to produce dtack14.
This is all part of the bus logic to make the 14MHz cpu look like a 7Mhz cpu to Gary & co. That part looks fine to me.

[Mathesar]

Originally Posted by erikarn

here's some traces during autoconfig in diagrom! all done in pulseview.

The second trace is interesting. There are two read cycles here with the first one asserting dtack a bit later then the second one. Both cycles finish without wait states though. Maybe that is something?

[ToeJam]

Hi all,
Total noob here. i am reasonably confident in soldering, not so much with surface mount tho. But I do want to try to build this card. The issue im having is interpreting some of the IC’s. When I search with the part number from the BOM I get a long list of IC’s that have similar numbers but seem to perform different functions.
Would I be OK to order the parts below?

U4,U9 CD74ACT02M96
U5 - SN74HCT74DRG4
U6 - CD74ACT112M
U7 - 74HCT4046AD,112
U8 - SN74ACT08DRG4
U10 - MC74ACT32DR2G

U1, U3 and U11 im OK with.

Sorry if this has been covered already or am asking in the wrong place, you can blame Glen M his video inspired me to try it

Thanks Mathesar for a great project.

[erikarn]

Originally Posted by Mathesar

The second trace is interesting. There are two read cycles here with the first one asserting dtack a bit later then the second one. Both cycles finish without wait states though. Maybe that is something?

hi, yeah, they're bus transactions.

lemme go set it up again and include /OVR in the trace.

[erikarn]

Originally Posted by Mathesar

AS7 is a delayed version of AS14.
Dtack7 is sampled at the falling edge of the 7mhz clock to produce dtack14.
This is all part of the bus logic to make the 14MHz cpu look like a 7Mhz cpu to Gary & co. That part looks fine to me.

it looks like /AS14 going high is asserting the flipflop /clr signals, which is clearing DTACK14? Ie, it doesn't wait for the bus to release DTACK7 before DTACK14 is released?

[Mathesar]

Originally Posted by erikarn

it looks like /AS14 going high is asserting the flipflop /clr signals, which is clearing DTACK14? Ie, it doesn't wait for the bus to release DTACK7 before DTACK14 is released?

That's right and normal 68000 behaviour. Once /DTACK is sampled low in S4 (bus state) the CPU will continue and de-assert /AS at the end of S7. It will not wait for /DTACK to be de-asserted.

[Mathesar]

Originally Posted by ToeJam

Hi all,
Total noob here. i am reasonably confident in soldering, not so much with surface mount tho. But I do want to try to build this card. The issue im having is interpreting some of the IC’s. When I search with the part number from the BOM I get a long list of IC’s that have similar numbers but seem to perform different functions.
Would I be OK to order the parts below?

U4,U9 CD74ACT02M96
U5 - SN74HCT74DRG4
U6 - CD74ACT112M
U7 - 74HCT4046AD,112
U8 - SN74ACT08DRG4
U10 - MC74ACT32DR2G

U1, U3 and U11 im OK with.

Sorry if this has been covered already or am asking in the wrong place, you can blame Glen M his video inspired me to try it

Thanks Mathesar for a great project.

Looks good to me, make sure all IC's are listed as SOIC (SMD parts with 0.127mm pitch between the leads)

[ToeJam]

Thank you,


PCB’s are on the way and I will order the parts making sure IC's are SOIC, cant wait to give this a try. I really appreciate l for the assistance. I’ll let you know how I go.



Cheers,

[sovietconscript]

I'm a bit late to the party here but would this accelerator work in an A2000? Also since my soldering skills are pretty much nonexistent is there anywhere to purchase one of these pre-made?