12 ms·
One of my first jobs in the early 90's was to write a device driver for a floppy disk drive in an embedded system. There was the drive itself, the floppy disk c
by anotherevan 3y ago
One of my first jobs in the early 90's was to write a device driver for a floppy disk drive in an embedded system. There was the drive itself, the floppy disk controller chip, and the direct memory access (DMA) chip. I only had the specs for the latter two in English.
Analysing the circuits, I saw the controller chip was wired such that use of the DMA chip was software configurable, so I thought beaut, I'll write and test the first iteration without DMA, then add and test that after.
Couldn't get it working. Scratched my head for a while until, while discussing it with one of the hardware engineers, was told that while the controller chip had been wired software configurable, the floppy drive itself was hard-wired to use DMA. If only I had the spec for that I would have figured it out!
So added usage of the DMA chip… success!
- bogantech 3y agoWhat kind of floppy drive was this? PC and just about every floppy drive I've ever seen only has motor, step, read / write data etc signals and no concept of DMA etc which would solely be handled by the FDC itself
- anotherevan 3y agoIt looks like a fairly standard floppy drive. I might be misremembering or misinterpreted the particulars due to neither me and the hardware guy being able to speak the other's native tongue that well, but the upshot was despite what the circuit told me about the configurability of the controller chip, it was not going to work without DMA.
- kimixa 3y agoThe linked article shows the "standard" pinout for a 3.5" floppy drive, and it's clear the interface is below the level of anything like DMA. I assume even if you were using something that looked like a standard floppy drive, it was using a higher level interface, or was including something like the controller ISA board in the "interface".
- pictureofabear 3y agoAre you Australian? After "beaut" your whole comment flipped to an Aussie accent.
- anotherevan 3y agoWell I wrote the whole thing with an Aussie accent. "Beaut" was just the first giveaway. :-)
- segfaultbuserr 3y ago> If only I had the spec for that I would have figured it out! It turned out that "vendors not providing datasheet" has forever been the problem for hardware developers.