From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Wed, 13 Mar 1996 20:46:45 -0500
From: jim mckie jmk@plan9.bell-labs.com
Subject: cant start 9pcfs
Topicbox-Message-UUID: 40574dea-eac8-11e9-9e20-41e7f4b1d025
Message-ID: <19960314014645.7J9B3dRM3fJOrSK3twfyFzT-R_UPZjj3Ar6DufcRMYQ@z>

the interrupt on 7 is a spurious interrupt generated by the interrupt
controller at reset. not to worry.

man plan9.ini has an example of setting up a serial line as a console.
perhaps then it will be clearer what's going on.