VIC-20 and SD2IEC

[nafmo]

Hi!

The README says:

vic20_jiffy_1541.d64: (...) This should also work on an SD2IEC, although this is untested.

I can verify that it does indeed work, as can be seen in this image: https://social.vivaldi.net/@nafmo/115306105100040880

Now to see if I can get the C64 version to work from the SD2IEC, I guess I will need to build a custom image for that?

[davidgiven]

Nice! How's the performance?

Re C64: currently there's no JiffyDOS fastloader. I got so burnt out doing the Jiffy stuff for the Vic20 that I couldn't face the C64 side without a break. Maybe soon.

[nafmo]

Performance seems to be decent, I only tested it briefly last night (ran a few commands, opened the BASIC interpreter). It didn't feel like I had to wait for anything to finish, which is nice.

As to fastloaders; My VIC-20 (and C64) does have built-in JiffyDOS. Can the BIOS for these use the kernel routines for data transfers and thus benefit from the fastloader when installed, or does it have to bypass it completely to be able to read the CP/M filesystem?

[davidgiven]

One good test is to try and assemble bedit.asm, which almost entirely I/O-bound, and on real machines the performance varies from slow to very slow. Sadly, I expect the VIC is not a brilliant development machine, as every test assembly would require saving the program, exiting the editor, doing the assembly, then reloading the editor and the program...

Regarding using the kernal disk routines: the kernal is not really designed to play nicely with other operating systems and has variables scattered all over the memory map, especially in zero page, which drastically limits CP/M's available memory (CP/M wants contiguous memory areas). The C64 port used to do this and it was just about workable, but IIRC you lost a complete 16kB of RAM due to needing to keep the kernal ROM mapped to handle interrupts? And IIRC there was a technical reason why this couldn't be done on the VIC but I can't remember what it was.

[nafmo]

I don't have my VIC-20 connected on a daily basis, so I haven't got around to test. And curiously yesterday when I tested it, it didn't load. Weird.

I doodled some ideas on how to get this to run with the SD2IEC, or other similar devices that aren't CBM DOS devices (i.e., can't run 6502 machine language code):

A D64 mode first: Mount a D64 to allow for the direct sector read/write operations, but write a BIOS/BDOS that calls the official CBM kernal routines directly for all access. This would allow a JiffyDOS-enabled machine to use that, since SD2IEC firmware supports the JiffyDOS protocol natively. Will be dead slow without, except for perhaps a C128 with 1571 or 1581.

Then a raw mode driver: The SD2IEC firmware allows the user to detect if a D64 is mounted or not (IIRC, it asks you to read track 1 sector 1 and check for error). In raw directory mode, there are enhanced commands for direct file access, like positioning in a file and getting the exact file size, so it might to be possible to bypass the entire CP/M filesystem and just read the files using the native protocols. Since CP/M only supports 8.3 filenames, anything else would just be ignored (just like running a MS-DOS session inside OS/2, it just doesn't see any files that have names that do not fit in 8.3). One would need a CHDIR (and MKDIR) command, though.

I haven't done any serious Commodore software development for over 20 years, so I'm not sure if I could get any of this up and running. Would be a very fun project to implement, though.