Yep that's broken, I'll fix it. Thanks for the report

Great, I’m curious to see how you’ll do it

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Jonathan Foucher

Take a look at the Planck 6502 computer.

I've committed a fix. I haven't managed to test it as I have broken my build else where.

Hoglet has kindly tested this and fixed a few issues. I have also fixed my build, but haven't tested it yet.

Right, that works perfectly now. Here is the output I get when running the 65C02 tests:



Thank you both!

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Jonathan Foucher

Take a look at the Planck 6502 computer.

NICE!

After messing about with the ARM assembly code for quite a while, I gave up trying to use it for this purpose. I could not familiarize myself with ARM assembly quickly enough to not run out of patience. Interacting with outside code written in C was a particular difficulty. So I decided to just throw fake6502 in there, and the performance impact is significant, but not enough to put the idea in jeopardy.

VGA output works fine (using a modified scanvideo from pico-extras)
I have added input from a PS/2 keyboard which is really easy to make work on the Pico.

Now, BASIC works fine, even though there is stille work to do implementing more VIC and VIA registers (I did the minimum VIC emulation to get BASIC working, and the minimum VIA emulation to get the cursor to blink

I have also included a schematic, in case anybody wants to try and run the code on their Pico.

Finally, here is a hello world gif:



You can also watch the full video

If you like, the full code and the beginning of a hardware design is in the github repository

Edit: a uf2 file ready to upload to your pico is here: https://github.com/jfoucher/picovic/releases/tag/0.01

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Jonathan Foucher

Take a look at the Planck 6502 computer.

(I wonder if Dave or Dominic could sketch an example of calling a C function from within the fast 65c02 model?)

There were actually very helpful already, and I managed to call C functions from assembly (to read from and write to memory for example) but interrupts proved to be too much of a challenge for me...

Anyway, for the time being fake6502 is good enough but I'll probably revisit the assembly code at some point in the future.

Regarding next steps, I would like to implement LOAD and SAVE from an SPI SD card adapter. Are there any resources anyone would recommend for doing that? Commodore filesystem specifications would be nice, as well as the translation that the 1541 performs between the data stored on disk and what is sent to the VIC-20.
Thanks for any resources you can point me to.

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Jonathan Foucher

Take a look at the Planck 6502 computer.

It's great progress anyway! (Sorry, can't help with the Commodore file formats questions)

On CBM machines the DOS runs in the drive, which basically is a small server; the computer sends requests over a serial bus (for the VIC-20 and C64; it's a parallel bus for the PETs) along the lines of "open this file" or "send these data" and the drive replies. So the computer itself knows nothing about the filesystem or FDC.

I think that by far the fastest and easiest thing to do would be to implement the hardware for this bus and then plug that into an actual device such as an SD2IEC (or even a real Commodore drive). You'd need to emulate just some of the PIO functionality of a 6522 VIA and use that to run GPIO pins that eventually go out to a DIN-6 connector. If you get clever you don't even need full level translation between the 3.3V GPIO pins and the 5V bus because the bus uses pullups (the output pins only ever pull bus lines to ground).

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Curt J. Sampson - github.com/0cjs

I hadn't thought of doing it that way, because I don't have an SD2IEC device, only an SPI adapter for SD cards, but it's actually a pretty good idea. I also think the sd2iec firmware should give me some inspiration if I was to go the SPI adapter way.


Good to know, but I already have a 74LVC4245 on the board for the PS/2 port with 6 free pins, so I might as well use it.

if you have any info about what the DOS on the disk drive does, that would be good to have. I find looking at a spec and implementing it is sometimes easier that looking at preexisting code and trying to adapt it.

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Jonathan Foucher

Take a look at the Planck 6502 computer.

Progress is slow but steady. I managed to read data from the SD card attached via SPI using this great library.

I had to modify it a bit because of DMA / IRQ conflicts with the code I am using for the VGA output.

Then, though a combination of this diskimage.c andthis format description I managed to parse a .d64 file that is present on the SD card and output (to serial) a directory listing like you would get when running as well as raw file data.

I have started hooking directly into the kernal routines from the C code to load the data and put it in the accumulator. Basically the C code detects if the PC is at the start of a serial input routine, set the A register to a byte read from the .d64 image at the correct offset, and sets the PC to the end of the input routine. This seems to do ... something, although not the correct thing.

I'm still not sure whether the 1541 does any translation between what's on the disk and what is sent through the serial bus. If anyone has info on that point, it will be more than welcome. Otherwise I'll have to dig into the sd2iec firmware, which is pretty complex (because it seems to emulate many devices and handle various fast loaders).

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Jonathan Foucher

Take a look at the Planck 6502 computer.

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

Thanks for all the great info. Hopefully I can at least get load and save of prg files working

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Jonathan Foucher

Take a look at the Planck 6502 computer.