25 Jan
1999
25 Jan
'99
1:26 a.m.
> Any Unix clones for 8080/Z80 systems? It ought to
be doable, given that the
> original Unix was done on a 64KB address space machine...
The problem with any multi-tasking or multi-user
system on a Z80 is that
there is no easy way to write position-independant code. There is no
relative call and no relative loads/stores (both the PDP11 and the 6809
have them). There are workarounds (either you use RST instructions to
simulate the relative call, etc or you relocate the task when you load
it), but they make life a little harder.
Most multi user/programming atempts for Z80 systems (and
6502 which had also (long) relative jumps) I know did go
for bank switching, where the whole 64K mem, minus the
OS parts, was banked for each task - so every programm
had a fixed starting address, and a maximum mem size,
based on the bank size.
Gruss
H.
--
Ich denke, also bin ich, also gut
HRK