Running an LSI-11 from UNIX V6

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It is relatively easy to run a hardware LSI-11 (or PDP-11/23, PDP-11/73, etc, although this article will use the term 'LSI-11') from a PDP-11 (either real or simulated) running Unix V6.

If one connects the LSI-11's serial line console to a serial line on the Unix V6 machine (either real or simulated), a program ('ttytalk', see below) exists to allow a user logged into the Unix machine to talk to the console, load programs into it, etc.

One issue is that Unix V6 does not allow 8-bit output on serial lines; this capability is needed to load binary files into the LSI-11. A small change to the shared serial line driver, dmr/tty.c, allows this.

Since the mode word in stty/gtty is already full, one has to extend the device interface to support setting and clearing 8-bit output support. One can either add ioctl() or do an upward-compatible extension to stty/gtty (see external link below).

The same interface is used to send a BREAK down the serial line to the console (used to halt the machine, e.g. when it is in a tight loop).

External links