after synch negotation during device probes, the 53C94 stops with the target
reqesting more command data. The fifo appears to still contain a couple of
bytes, so transfer them. If the target still wants command data after that,
do a transfer pad. The target seems to function normally after this. A
much better solution thant simply rebooting!
Also fix a problem when compiling with DIAGNOSTIC - a mismatch between using
DIAGNOSTIC and MACH_DIAGNOSTIC caused the compile to fail.
Try to start another target and a device disconnects.