dove@mit-dspg@sri-unix (06/11/82)
Date: 1 Jun 1982 11:39:13-EDT If you poll the hardware, you must do so at sufficient speed for them not to overfill (unless you use the alarm). Lets assume that you want to connect local systems with 9600 baud lines. With 2 lines coming in at 9600b you can expect 2000char/sec into the silo so you must poll within 2000/32->60hz to catch the silo at most half full. More active lines means you nees a real-time clock for timing your polling routine. Thus the primary reason for the alarm is to allow you to poll at a more reasonable rate like 5hz rather than several hundred. The reason for twiddling the silo alarm level, is that if the silo alarm is the only interrupt ever serviced (assuming the polling interval gets reset whenever the silo alarm is triggered) the system runs at peak efficiency . This latter optimization is probably not that useful though.