20 Jun
2009
20 Jun
'09
2:37 a.m.
>>>
On Behalf Of Gordon JC Pearce
On Fri, 2009-06-19 at 18:59 +0100, Tony Duell wrote:
Oe perhaps one little one... I'd rather spend my
time working on the
hardware of a machine I do own (and I am not short of things to do...)
than running an emulator for a machine that I don't.
I've spent time writing an emulator for a machine I don't own and for
which I have a certain amount of documentation.
<<<<
I've written a couple of emulators a long time ago.
The more memorable one being for the F8 microprocessor that ran on the ICL
1900, was written in
assembler (probably GIN5, might have been PLAN) and whose execution speed on
the mainframe was
almost the same as for a real hardware F8.
The difficult decision was whether to follow the documentation or the real
hardware in a very
common situation.
On the F8 after a jump instruction
according to the doumentation the contents of the accumulator became
undefined
in the real hardware they were very well defined, but totally wierd: the
low order 8 bits of the jump address.
after some discussion with the department who was teaching this micro, the
emulator corrupted the accumulator
but to a different value. So in one sense it was not a correct emulator;
but in another it was a far more useful
development tool.
Andy