Raven. A homemade Atari-like computer

[PhilC]

I couldn't resist.. expecting it could be a pretty fun and quick(?) project making a Tos driver for floppy disk on the isa bus when it arrives.
It comes with IDE, parallel and two serial ports too but I'm not sure I need many more of those things :lol:

s-l1600.jpg

(Yes, I am fully aware of how pointless it is :))

You keep pinching my ideas Mr Granlund. I wonder if my workshop is bugged? :lol:

[agranlund]

You keep pinching my ideas Mr Granlund. I wonder if my workshop is bugged? :lol:

In that case, there's a very high chance you'll beat me to it and I'll be very happy to test-drive your code :)
I have so many other things I want to play with, when time allows.

[PhilC]

You keep pinching my ideas Mr Granlund. I wonder if my workshop is bugged? :lol:

In that case, there's a very high chance you'll beat me to it and I'll be very happy to test-drive your code :)
I have so many other things I want to play with, when time allows.

Oh I very much doubt it :lol: I may not work any more but have a list as long as my arm with jobs to do.

[dml]

I have a question. When populating the RAM SIMM slots - do the RAM cards need to be populated starting from slot 0? Would it work if just slots 1 & 2 were filled?

[sety]

I have a question. When populating the RAM SIMM slots - do the RAM cards need to be populated starting from slot 0? Would it work if just slots 1 & 2 were filled?

I think slot0 is mandatory, I'm sure I have read that somewhere, but now that I have a working system I'll go check for you right now. :)

Yep! You need slot0 populated

[dml]

I think slot0 is mandatory, I'm sure I have read that somewhere, but now that I have a working system I'll go check for you right now. :)
Yep! You need slot0 populated

Thanks for checking that.

If I'm reading the schematic correctly, it appears the SIMM sockets are routed with only pins 68+69 (OE/WE) differentiating each slot. So the phyiscal ordering of the RAM slots could be reversed (slots 0 & 2 could be swapped around), by re-routing just 4 tracks?

[sety]

If I'm reading the schematic correctly, it appears the SIMM sockets are routed with only pins 68+69 (OE/WE) differentiating each slot. So the phyiscal ordering of the RAM slots could be reversed (slots 0 & 2 could be swapped around), by re-routing just 4 tracks?

They seem to go to the 1508 so you could probably even do it in firmware without having to cut anything! I'm super curious though.. Why? I'd love to know what you're planning. :)

[dml]

They seem to go to the 1508 so you could probably even do it in firmware without having to cut anything! I'm super curious though.. Why? I'd love to know what you're planning. :)

That's a good point - noted!

Slot 0 is both mandatory and very close to the CPU. Anything added in the CPU area which takes up extra space would interfere with the mandatory slot first.

I'm thinking it could be a beneficial mod to reverse the slot ordering (just for the RAM, not the ROM), rather than trying to move slots away from the CPU (which would obviously be a huge re-layout effort, likely impractical and not worth the trouble).

In my case, I have a nice, black-anodised passive cooler which is made to fit over the top of a 040/060 CPU, with a square slot milled out for that. That makes it is bigger than the CPU with a skirt around all 4 sides - unfortunately interfering with slot 0 socket just enough to be a problem.

I was hoping to avoid a CPU fan - partly the noise & inevitable rattling/sticking but also sucking dust into/around the board constantly - and was considering a trade for the optional RAM slot vs silent running, with the option of changing it at any time to populate the last slot.

Still plenty left to do before deciding on that one though.

[agranlund]

I think slot0 is mandatory, I'm sure I have read that somewhere, but now that I have a working system I'll go check for you right now. :)
Yep! You need slot0 populated

Thanks for checking that.

If I'm reading the schematic correctly, it appears the SIMM sockets are routed with only pins 68+69 (OE/WE) differentiating each slot. So the phyiscal ordering of the RAM slots could be reversed (slots 0 & 2 could be swapped around), by re-routing just 4 tracks?

Yep that should be doable.

Alternatively, and this might be easier, is to change pin setup in the ATF1508 bus logic:

Code: Select all

pin 44 = !RB0RD;
pin 45 = !RB0WR;
pin 46 = !RB1RD;
pin 48 = !RB1WR;
pin 49 = !RB2RD;
pin 50 = !RB2WR;
pin 51 = !RB3RD;
pin 52 = !RB3WR;

You'd need the WinCUPL software to rebuild it. It's old and finicky but it's free :)
In my installation I have replaced the fitter executable with the slightly newer one found in ProChip 5.0.1 but I'm not sure if you'll need to do that or not. Probably not.

And the third option would be changes in the bootloader software only.
Right now the bootloader requires slot0 for stack and working ram but in theory it should be possible to let it use the first slot found.
You'd probably need to add a small mmu table setup quite early in that case, and then the proper mmu setup during the final stages may need some changes. (or keeping just the one mmu setup but moving it to way earlier in the boot)

Now you have three options :)


Edit: I do like the third options regardless, and if someone else doesn't implement that I might do that some time in the (distant) future as it feels like it would be a fun thing to do.

[agranlund]

Slot 0 is both mandatory and very close to the CPU. Anything added in the CPU area which takes up extra space would interfere with the mandatory slot first.

I'm thinking it could be a beneficial mod to reverse the slot ordering (just for the RAM, not the ROM), rather than trying to move slots away from the CPU (which would obviously be a huge re-layout effort, likely impractical and not worth the trouble).

Ah, that's a good point!
We can make the ram slot order reversed in the firmware from now on.