make DMA jobs record checkum of read data.
fix stupid bug in drive led OSD.
make OSD drive light be 16x16 pixels instead of 4 pixels high
and full display width.
fix bug with constraining drive led OSD to 16x16 pixel box.
more work towards F011 FDC emulation on sd card.
implement simulated motor stepping.
fix bugs in previous commit.
make $14 time, but not step.
annotate DOS track stepping routines.
write data to F011 FDC sector buffer while reading.
C65 ROM expects sector found flag to remain high after reading
completes.
annotate more of DOS ROM.
more DOS annotations
actually trigger sd controller to read sector when FDC read
sector command is submitted.
fix error in dos annotation, and add some more.
make flag_eq in FDC be properly maintained.
don't allow FDC to write beyond end of disk image.
move sw15 test to after loading ROM and mounting disk image etc.
add code to search for C65GS.D81 for mounting as internal disk.
actual mounting not yet implemented.
update behaviour of FDC run flag following rereading of specifications.
work towards being able to read/write FDC buffer from CPU.