CBUF.LIB
OVERVIEW: The circular buffers here are standard rotating FiFO buffers.
THey are currently used by the RS232 serial library to store
incoming and outgoing data, but they are general purpose.
This program uses the HF flag of a FiFO to trigger reads, guaranteeing that the FiFO is never blocked for the writer, giving high throughput for the reader (bursts of D/2 = 128) and guaranteeing that the the reader will not be stuck in the top half of the FiFO.
