All,
In looking at bootloaders I have observed some interesting SimH behavior
and I am hoping y'all might have something to say about it.
In sum, is it possible to deposit values directly into the I/O registers
from the sim> prompt, if so, can you provide an example using the RK or
RP command register?
I have tried the following in the default PDP-11/73 with 4MB Memory:
PDP-11 simulator V4.0-0 Beta git commit id: 0f43551d
sim> d 17777410 177540
Address space exceeded
This would seem to answer the question in the negative. However, if I
then put info into the buffer by typing in some machine code and
executing it directly:
PDP-11 simulator V4.0-0 Beta git commit id: 0f43551d
sim> id 10000-10006
10000: 012737
10002: 177540
10004: 177410
10006: 000000
sim> g 10000
HALT instruction, PC: 010010 (HALT)
and then reference the I/O buffer in SimH:
sim> ex 17777410
17777410: 177540
The I/O buffer now appears to be available for examine.
sim> ex 17777410
17777410: 177540
And for deposit:
sim> d 17777410 177530
sim> ex 17777410
17777410: 177530
Interestingly, Address space exceeded doesn't appear to be a problem.
What is going on with SimH's PDP-11 simulation. Is the device not really
"there" until it is referenced from a machine code program, or is the
17777410 address not initialized until the device is accessed, or what?
Thanks,
Will
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