[Simh] Way out idea for simh

[Sampsa Laine]

> On 20 Apr 2016, at 21:54, Paul Koning <paulkoning at comcast.net> wrote:
> 
> Let me flesh this out a bit, I think I understand your idea and it's a pretty straightforward one.  It vaguely looks like a pseudo device implementation of the GDB remote stub file access setup.  Or, I suppose, vaguely like FTP requests; they two are the same thing at a sufficiently superficial level.  :-)
> 
> Consider a new type of device exposed to the guest software.  You can send it commands: read a file, write a file.  After that command, you read from the device to get the file data, or write to it to send file data.  End of file is an I/O status code (for read) or some special device operation (for write).
> 
> From the application point of view this isn't all that different from guest OS file read/write calls, except that (a) it's sequential only I assume, (b) the operations are represented as device operations rather than being handled as OS calls.
> 
> What you need for this to work is a way to talk to a raw device.  That means directly, if the OS allows it, or if you don't have one.  Or via a very simple device driver if one is required.  For example, on RT11, or an IBM 1620, you could do the I/O directly. On RSTS you'd either need a driver (which is a pain) or do it through a sequence of "peek" and "poke" operations (not too bad).
> 
> Yes, that seems like a notion that could be interesting.  It would be good to do an existence proof, on some not too difficult machine.  Perhaps a PDP11 or PDP8, with the "direct to the device" approach.

This is already implemented in the SIMH Altair emulator actually…


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