Integrated Tashtari Machine: Floppy Drive Emulator

[Tashtari]

Whoo, long time since I've updated this thread.

The USB frontend with the PIC16F1454 did not pan out, unfortunately. I think it behooves me to return to the idea of a more Floppy Emu style frontend, probably targeting the PIC16F1788 and its whopping 2 kB of SRAM. I have the hare-brained idea that I can keep three sectors in memory at a time and that'll be enough - the current sector on the current side, the next sector on the current side, and a sector on the opposite side at the ready for if the SEL signal suddenly flips. With some trickery in the way the SD card is formatted (FAT32 with a big cluster size), I can actually keep a cluster map of a whole floppy disk image in what remains of the SRAM, and thus avoid the fragmentation problems that seem to be plaguing the Floppy Emu lately...

I still would really like to figure out a way to make an RPi act as the frontend. If I could just get the latency down to the point where it could deliver data in time for the backend, that'd make so many things so much simpler - build a backend and your frontend is "download this image onto an SD card and stick it in your favorite RPi". Unfortunately, SCHED_FIFO and dedicating a core to the frontend process isn't enough. PREEMPT_RT might be enough, but there's an awful lot of outdated documentation on the subject of real-time Linux and I haven't unwound it yet.

So much to do. But a life full of projects is a life well-lived, so I press on.

...Oh, and I'm calling it TashFloppy now. I've got a brand to maintain. =)

 

[LaPorta]

I’d pay big money if you could get it to read SD cards with GUID mapping and MacOS Extended formatting .P

 

[Tashtari]

I’d pay big money if you could get it to read SD cards with GUID mapping and MacOS Extended formatting .P

While I know they're ultimately just block devices that can have any filesystem on them... I'm fairly sure that the SD spec mandates that they use MBR and FAT for the sake of embedded devices. Is Mac OS not respecting that these days?

 

[cheesestraws]

Is Mac OS not respecting that these days?

macOS does what it always does, when you erase a block device it will default to the previous filesystem but let you choose another. It won't stop you creating a GUID / HFS+ filesystem on an SD card, though the result will be of somewhat limited use. I have used this, though, to transfer mac files around when I couldn't find a USB stick.

 

[LaPorta]

It’s more that whole bit of transferring files is easier if I can just stick the SD card into an old Mac that already has the files I need. I know, I’m the exception here!

 

[Tashtari]

Well, if I can get the RPi working with PREEMPT_RT as the frontend, you should be able to mount any filesystem that Linux can read. I made up an RPi hat for that purpose and have sent it to JLCPCB to be fabbed, so now it's just ("just") a matter of the software side of things... that'd be my preferred solution anyway, so fingers crossed.

 

[LaPorta]

This is a great project no matter what!