750 hanging at boot time..

[Guy Harris]

> I am having problems with two 750's hanging at boot time.
> Right after the line printer (lp0) is configured, everything
> stops until you hit a key (any key) on the console.   It
> then proceeds fine with "Automatic reboot in progress..."

This is a common problem.  It occurs if you have a slow printer as your
console which is set up to transmit XOFF and XON for flow control, and if
you're running an operating system that does a lot of printing before it
starts the terminal driver running normally on the console (like 4.xBSD
which prints a lot of messages while doing autoconfiguration).  The
DECwriter sends an XOFF, which is ignored by UNIX at that point; it probably
sends lots more XOFFs.  Once the terminal driver is started up, it receives
an interrupt because of the XOFF in the receiver buffer.  It dutifully stops
all output.  For some reason, no matching XON makes its way into the driver.
Typing any character tells the driver to restart output.

> It only does this on the machines with lp interfaces...

This is probably because if you don't have an lp interface it doesn't print
enough to overrun the DECwriter's buffer.

One solution is to tell your console not to transmit XOFFs (it is a SET-UP
option on the DECwriter).  Another option might be to start the terminal
driver up sooner...

	Guy Harris