3 Dec
2004
3 Dec
'04
1:49 a.m.
On Fri, 3 Dec 2004, Tom Jennings wrote:
I've been trying to recall, with no success, how
subroutine
calls were implemented in the 8x300. I used to write code for
this weird thing (realtime video processing) and the assembler
I used (some horror that ran under TSO) hid it from me so I
don't have a clear recollection of the method.
It's a really weird CPU, "subroutines" were essentially jumps,
as in a lot of machines, but the "return" was through some
strange jump table or something.
Once upon a time there was a website with CPU instruction cards
(man I had a huge pile of these things, pitched loooong ago...)
but I can't find it. Nothing on bitsavers I can find.
If its the same as the SMS300, My old Osborn introduction to microcomputers
says:
"The SMS300 has no subroutine or interrupt handling logic" ... "subroutine
logic can be created with an XEQ instruction and an appropriate jump table,
but this is rather clumsy, in most cases it would be simpler to do without
subroutines"
Isnt the 8X300 a predecessor to the PIC somehow?
(There's also some really bad info out there on the origins
of "Harvard" architecture, attributed to some stupid hardvard
vs. princeton microprocessor design thing. Please -- about 40
years earlier: that asshole Aiken. No one liked him anyways.)
Peter Wallace