When 24000000 gives you a factor 4, what happens when you set IOBZCLOCK to 6000000?
With the clock set to 6000000, I get:
reva: {2} cu -f -s 115200 -l /dev/ttyC0
cu: unsupported speed 115200
reva: {3} cu -f -s 57600 -l /dev/ttyC0
cu: unsupported speed 57600
reva: {4} cu -f -s 38400 -l /dev/ttyC0
Connected
?????????????????????????????????????????????????????????????????
I tried every baud rate on the other end from 300 baud to 230400, and I
just got question marks or nothing.
Hmmm... John