On Fri, 22 Apr 2022, "Maciej W. Rozycki" wrote:
You can of course build a PCI FDD interface around the NEC uPD765 or an equivalent controller, but you can't make it compatible with existing PC software, because too much PC specifics has been embedded there around the 8237 DMA controller and DMA page registers at fixed port I/O locations, which is inherently incompatible with the PCI decoding model.
Yes, but I have never understood why you would need BIOS compatibility. Current operating systems have their own drivers. I mean, what would be the problem to write a, say, Linux driver for such a thing? And you don't even need DMA for the FDC if you want to make it cheap. OTOH a small dedicated SRAM and supporting microcontroller on the PCI board would make up a great PCI floppy controller.
A feasible solution is a SCSI FDD option, such as the DEC RX23 device (which is actually a whole embedded microcomputer built around an 8080 CPU and using an 8237 DMA controller, an 8259 interrupt controller, a uPD765 floppy drive controller and a 5380 SCSI interface), which works as a removable drive with any single-ended parallel SCSI host adapter, e.g.:
I have a DaynaFile II, it was once an external SCSI 5.25" FDD with proprietary protocol, designed for crappy Apple computers. I had disassembled the firmware and documented the command set. And I think that I have redrawn the schematics at that time. It is much more capable of what the Apple driver might have supported. The hardware itself is just a small board with a DP5380, 80C31, a 32kB SRAM and 2793 FDC. So everyone shouting for a solution, I recommend looking for existing ones and eventually (re)build one from scratch. I mean, today you just need the FDC and a microcontroller with integrated USB or whatever to communicate with the host.
(Note: of course this applies only to standard IBM formats) Christian
