02-06-2016, 11:13 AM
(02-06-2016, 10:56 AM)obo Wrote: I've not (yet) tried writing weak data out using the SCP, but it's on my list once I've restored write support.
Though I have been successfully writing weak areas using the standard PC floppy controller, with a few multi-pass formatting tricks. For weak areas on 250Kbps (@300rpm) tracks I found writing 0x07 byte filler at 300Kbps worked well enough to be read back unreliably at 250Kbps. I was doing something similar to you, but writing a full ID header and the DAM of the data field, with at least part the data field left weak using that technique.
It's relatively coarse in terms of technique, but seemed effective enough to lose FDC sync on all the drives and systems I've tried it on. I was planning on trying the same on SCP when I got to it, even though the SCP hardware is capable of something much finer grained. I'd be interested to hear if you find a better approach / pattern to achieve it.
It does somewhat depend how long you have in which to lose sync. I don't know so much about weak regions typically found in IBM/ISO style sectors but I get the impression you find weak regions of at least a millisecond? For that kind of region I emit a repeated fixed pattern but with a moving clock bit. Standard stuff.
However there are some pretty strict (read, stupid) protection formats on Amiga: I have one which reads 16 bits immediately following a sync word, and requires *those* to be non-deterministic. That's tough!
