8 Feb
2003
8 Feb
'03
1:57 p.m.
Yup, the 6502B I think it was. A nice system. - Jim
Jim Keohane, Multi-Platforms, Inc.
"It's not whether you win or lose. It's whether you win!"
----- Original Message -----
From: "Eric Smith" <eric(a)brouhaha.com>
To: <cctalk(a)classiccmp.org>
Sent: Saturday, February 08, 2003 19:45
Subject: Re: Designing around a 6502 (was Re: Assembly on a Apple IIc+)
Jim Keohane wrote:
alternate
> A 6502 task context
> would therefore require moving about 1KB, which would take about 4,500
> instructions (at one instruction per cycle.) On a circa-1980's
> machine, with a 1MHz clock, that would take about 4.5 msec.
Pat Finnegan wrote:
This gives me awfully devious ideas... First,
were there any
'multitasking machines' designed around the 6502? If you wanted to do
multitasking, it seems like you could design a fairly simple MMU that
would swap out the zero-page and stack (or all of the memory pages) for
different ones, depending on the running task. Leaving only a few
registers that need to be saved, it would leave a very small overhead
for task swapping.
The Apple /// hardware supports this. It allows you to select an pair of pages to replace page zero and page one.
AFAIK, it was never used
for user-level multitasking, but was used to provide separate user and
OS contexts.