[Simh] Radial Serial Protocol

[Bob Supnik]

Radial Serial Protocol was the brainchild of Eric Peters in the DEC 
Research Group, who later went on to found Avid, the video editing 
company. It was intended to be a "junior brother" of MSCP. The 
resemblance is most obvious in the use of command/response packets, 
rather than registers (or pseudo-registers) for programming. However, 
the two protocols were developed in parallel, by independent groups. 
MSCP was hammered out by the DEC Storage team doing the HSC50 in 
Colorado Springs; RSP went directly from the Research group to TU58 
development.

Because I had been the development supervisor for the HSC50 and UDA50 
feasibility prototypes in storage advanced development, I consulted with 
Eric on RSP before I moved over to microprocessor design in 1978. I 
don't have any memos from that era. Various web documents mention that 
RSP was unreliable because it lacked low-level flow control, meaning 
that there was no way to block character transmission (in either 
direction) once it started, even if the receiving UART was being overrun 
due to heavy I/O traffic at higher interrupt priorities. MRSP solved 
this particular issue.

/Bob Supnik