Reply 120 of 136, by FreddyV
migry wrote on 2024-03-24, 01:21:I have an interest in retro hardware and have been experimenting with replicating the original 8088 based PC on a set of PCBs fo […]
I have an interest in retro hardware and have been experimenting with replicating the original 8088 based PC on a set of PCBs for my own fun and education.
This is a very interesting card, in that I understand that it can replicate the floppy drive?
My design is simplified in that I did not implement DMA, as I felt it unecessary. The Tandy1000 also omits DMA and was nevertheless able to read and write data from/to the floppy disk controller IC (and was the inspiration). Unfortunately I have run into problems trying to get floppy I/O to work.
Again I get the impression that this card doesn't have DMA, so I wondered if the "virtual" floppy was accessed via I/O ports?
Sorry if my assumption is way off base(!), but if the "virtual" floppy doesn't use DMA, then presumably use of this card would need a custom BIOS or possibly an option ROM (which I again assume that it can emulate) to allow the INT13 floppy/HDD routines.
I just wondered if this card might be a way to help me get my hardware to boot DOS? I have my own minimal BIOS so I can change the floppy disk code if there was some alternative I/O based way of accessing the floppy hardware. I was already thinking about doing something similar to give me an I/O based floppy interface, speed is not an issue for me, possibly using a Teensy in a similar way. But there's no need to re-invent the wheel!
Again apologies (I found information unclear), but what bus speed does this card support? Does it stall the CPU using RDY/wait to extend bus cycle for faster CPUs?
Many years ago I figured a way to use a PIC to emulate a small specialised ROM chip which was no longer available and I had to find a way to return the data quickly enough for it to be read correctly. Thankfully the ROM it replaced was quite slow. I get the impression that the PICO must be doing something similar, but emulating both RAM and ROM and I/O ports?
Perhaps I should join the discord?
Anyway I think it is a fabulous project and yet another clever way of using modern cheap hardware to emulate parts (possibly unobtainable or expensive) of a retro computer. I am sorry to hear that the author was disappointed at the lack of initial enthusiasm from the retro community.
Hi,
Here is the Discord link:
https://discord.gg/BBTzShJQUw
My Board use only I/O, RAM Access and one IRQ. (It is working like DOSBOX)
The Floppy is not emulated, it has its own BIOS (Option ROM) that send the disk command to the Pico and the PicoMEM execute the full BIOS IRQ Commands.
It is done like this as it is much more simple and to be able to work with a real Floppy drive attached (In this case, the Floppy controller exist, so the board will be in conflict with it if it does hardware level emulation)
