[Simh] emulating rom in simh?

[Brad Parker]

Tim Newsham wrote:
>Is there an easy way to emulate a small rom (or map in small regions
>of additional ram) in simh?
>
>The boot procedures for 1st ed unix have a small ROM at 173700 but
>the RAM only went up to 57777.  We could just populate a full 64k
>of RAM and laod the ROM code into the appropriate place, but it would
>be nicer if we could be more realistic in the simulation.

We could make a "diode board" device, which would approximate the
original device they used.  As I understand it they had a unibus board
(probably a matrix of diodes) which they hand wired to produce the boot
code.  Not an actual rom, but worked like one.

One way to reproduce this would be to make a device which appears as
"rom" on the unibus to which you attach a file which contains the 
contents.  Or we could just hard code the contents as a default and
allow someone to attach a file to override the defaults.

It would be easy/quick to do, I think.  Several of the the current
devices include 'boot roms' already.

-brad