Sat Jan 25 07:56:29 EST 2020

interrupt driven tx

In the isr, keep pushing out data from cbuf.  If empty, disable the

To translate that into CSP signal flow, do the following:
- If there are more characters to transmit, keep going.
- When done, send a signal on the shared interrupt pipe

EDIT: Ok got it working.

Trick was to use both transmit ready and transmit done interrupts.

Next step is probably to also do the packet decoding in the interrupt.
Or maybe not.  Let's stick to bytes.