17 Feb
2025
17 Feb
'25
6:19 a.m.
On Feb 17, 2025, at 9:02 AM, Frank Leonhardt via
cctalk <cctalk(a)classiccmp.org> wrote:
On 17/02/2025 05:12, ben via cctalk wrote:
Indeed, but the subroutine call instructions were hardwired to auto-decrement on a
particular register, conventionally called SP (register 6 in the PDP-11). So while you
could create data stacks that grow in either direction, with a pointer of your choice, you
could only do calls via SP and only downward.
paul
Did any classic computers have a subroutine call
as (S++)=PC, PC=(EFA)
as well as the standard call (--S)=PC,PC=(EFA) ?
One could have a virtual stack machine, using helper functions without having to deal
with return addresses on the stack.
On the more than "one stack pointer" in the subject, it was a bit arbitrary on
the PDP-11 (or VAX) as the pre/post indexed indirect addressing made every register a
stack pointer.