Keeping the time

After some prior detection problems, B-DOS now correctly detects the SAMBUS real time clock. It writes values to the clock registers and expects to get them back - but the MAME implementation was ignoring writes and just returning the current time. After changing that, so that it returns the values written to it for some time, we get this:

It still hangs at the HD detection though, looks like the WD1772 controller needs to return some different values for it to fail (the HD controller is running on the same port as floppy drive 2).