27 Oct
2010
27 Oct
'10
5:28 p.m.
Chuck Guzis wrote:
Consider, for example, the CDC 7600. Each peripheral
processor (or
"channel" in alternative terminology) is hard-assigned a buffer in
SCM. The CPU has no way to talk its channels other than by writing
into these memory-mapped buffers. There are no CPU I/O ports or any
other way for the CPU to reach the outside world. The 6000 series
behaves similarly, but the PPUs get to read any memory address.
Typically, a "mailbox" is set up for PPU communication.
So, did Seymour invent memory-mapped I/O?
I suspect not.
I'd consider a channel using a shared memory area as a type of
I/O
distinct from either port-mapped or memory-mapped. And the CDC 7600
(and 6600) certainly didn't invent the idea of a channel.