Am 09.01.2012 21:11, schrieb Uffe Jakobsen: > > > ... > The 6508R2 along with the FDC chip 8723 and the ROM found between them > constitutes the floppy subsystem - just like every other external CBM > drive we know of - only with the difference that the DOS in its ROM is > not CBM DOS as we know it from the external drives. The subsystem > seems to resemble a traditional simple disk/floppy subsystem much more > than any CBM diskdrive that I know of - and yet is has its own CPU for > some unknown reason. The reason is quite simple: Due to the way unix schedules the processes, it cannot be guaranteed that the floppy gets enough CPU to read data fast enough. (Remember: We are talking about 1983 technology) Based on the functional description in the datasheet(*), the floppy subsystem was meant to be on a separate board, connected back to the 8716 DMA on the mainboard. Between unix and the subsystem was a SCSI-like protocol planned, perhaps in a way to reuse as much of the harddisk connection as possible. (*)I will try to copy as much as possible in a file later, unfortunately most of the pages are unreadable due to fact that it was made on a bad xerox machine long time ago. Message was sent through the cbm-hackers mailing listReceived on 2012-01-09 21:00:33
Archive generated by hypermail 2.2.0.