Acorn System FPGA

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hoglet
Posts: 6391
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Location: Bristol

Acorn System FPGA

Postby hoglet » Tue Aug 09, 2016 11:39 am

Hi Guys,

I've started work on an FPGA clone of the Acorn System family. Why? Actually I don't really have a good reason, other than it's an excuse to learn more about these systems.

I'm initially targeting the Papilio Duo, and later will add the Altera DE1:
IMG_0529.JPG

So far I've got the following implemented:
- 6502 CPU / RAM / ROM / System Via
- optional ICE T65 for debugging (very useful!)
- Keyboard
- VDU 40 (6845 + SAA5050)
- VDU 80 (6845 + Character generator ROM)
- Video switch and scan doubler

At the moment, I have the following software in ROM:
- System 3 OS (F000-FFFF) (MDFS link)
- System 5 OS (F000-FFFF) (MDFS link)
- Acorn New Basic (A000-DFFF) (MDFS link)

I'm intending the System model to be selectable with jumpers, which at the moment just switches between the System 3 and System 5 OS ROMs.

All the work I've done so far is in github:
https://github.com/hoglet67/AcornSystemFpga

What I have so far seems to boot, after playing a few tricks to fake a disk interface at 0A00.

The System 3 OS seems to include drivers for the VDU 40 board:
IMG_0526.JPG

The System 5 OS seems to include drivers for the VDU 80 board:
IMG_0530.JPG


Both seem able to run "Acorn New Basic" which I currently have included in ROM.

There's room for improvement in the keyboard and both video systems, but I think the real challenge will be a file system. The System floppy disk interface uses an 8271, and to my knowledge there isn't a VHDL or Verilog design for that yet. So if anyone does know of such an implementation (either against real floppies, or against an SD card), that would be very handy.

I'm wonder what, if any, other software exists that might run on this?

I might also explore the 6809 CPU card. But again, without a disk interface this is going to be a bit boring.

Dave

IanB
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Joined: Sun Sep 04, 2011 7:28 pm

Re: Acorn System FPGA

Postby IanB » Tue Aug 09, 2016 5:20 pm

hoglet wrote:I'm wonder what, if any, other software exists that might run on this?

The only System software I have is the level 2 econet file server:

system5.jpg


Here's the ROM image and file server software.
Sys5RomFS.zip
(47.4 KiB) Downloaded 23 times

Edit: Forgot to mention the ROM image is 8K and the first 4K is the Econet driver (E000-EFFF). You have to use *GO E003 to init econet. There are other entry points as well, see the system 5 manual for details.

hoglet wrote:But again, without a disk interface this is going to be a bit boring

You could try connecting the FPGA to an econet module and use econet as a file system but if you want to use the file server software you would have to get both econet and the disc interface working.

2nd Edit
There is also a copy of SMON on the disk image which is the UK101's EXMON machine code monitor modified to work on the SYSTEM 5
Last edited by IanB on Tue Aug 16, 2016 9:52 pm, edited 1 time in total.

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richardtoohey
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Location: Tauranga, New Zealand

Re: Acorn System FPGA

Postby richardtoohey » Sun Aug 14, 2016 4:00 am

hoglet wrote:I've started work on an FPGA clone of the Acorn System family. Why? Actually I don't really have a good reason ...

What I have so far seems to boot ...
=D> You are a wonder, Dave. (Sincerely). I used to try and keep up but ... 8-[ :?:

=D> and thanks for sharing - it's always fun to see what you are up to. :D

waltermixxx
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Location: Toronto

Re: Acorn System FPGA

Postby waltermixxx » Tue Aug 16, 2016 12:45 pm

Very cool :)

A DE1 version would be awesome, I have one ready and waiting ... ( It was running as a spectrum 128 recently, but I think we can do better than that with a nice variety of Acorn machines...) A lovely Acorn Atom with 12K and colour card would be awesome, then i will have come full circle with my first real computer...) :)

I think Atom would be good:

https://github.com/hoglet67/AtomFpga/tree/master/altera

is this it? if so I think I know what I am doing tonight. :)

more specifically: https://github.com/hoglet67/AtomFpga/tr ... ra/release

(I'm kinda new to FPGA boards... but I will give this a shot. :)

is there any documentation on what settings the switches should be on?
are they used on the DE1? :)

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hoglet
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Location: Bristol

Re: Acorn System FPGA

Postby hoglet » Tue Aug 16, 2016 2:55 pm

waltermixxx wrote:I think Atom would be good:

https://github.com/hoglet67/AtomFpga/tree/master/altera

is this it? if so I think I know what I am doing tonight. :)

more specifically: https://github.com/hoglet67/AtomFpga/tr ... ra/release

(I'm kinda new to FPGA boards... but I will give this a shot. :)

That's the one...

You need to write the firmware (schakelkaart.rom) into the DE1's ROM at address 0x100000. This is so it can co-exist with the Beeb and Electron FPGA firmware. This involves using the DE1 Control Panel App (Windows only), which is described well in the manual.

You then just program the sof or pof file using the programmer software.
waltermixxx wrote:is there any documentation on what settings the switches should be on?
are they used on the DE1? :)

Once programmed, just connect a PS/2 keyboard and a VGA Monitor.

The only toggle switch used is switch 0, which chooses the 6847 character set, so not that important.

The only push key used is key 0, which is a hard reset.

You can write the latest Atom Software Archive to a small SD Card:
viewtopic.php?t=6544

Dave

waltermixxx
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Location: Toronto

Re: Acorn System FPGA

Postby waltermixxx » Tue Aug 16, 2016 9:12 pm

Excellent my S100 IMSAI Mini system can wait a bit while I get this Acorn Atom up and running. I will post pictures once I do. Cheers.

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roland
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Re: Acorn System FPGA

Postby roland » Tue Aug 16, 2016 10:14 pm

I think it would take some reprogramming of the CPLD's to turn the Atom2k15 into a SYSTEM-compatible computer as long as it uses text only programmes that correctly call the OSWRCH/OSRDCH mos entry points. With a small hardware mod it would also be possible to switch between Atom and System-mode.

But why bother if there's only some file sharing software available ... ?
256K + 6502 Inside
MAN WOMAN :shock:


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