slightly, but autoinitialize mode is impossible to use reliably, since it
means that if disc interrupts are blocked for long enough (or sec_copyout
is too slow), the uPD71071 can run off the end of a block before the
base registers have been updated and end up processing the same block
twice. With this change, the SEC in my A540 seems finally to be solid.
driver uses the board's DMA system, uses the machine-independent WD33C93
driver, works on NetBSD/acorn26, and doesn't share a name with six other
machine-dependent SCSI drivers. Not tested on acorn32, but it seems to
work tolerably well on my A540.