DEC Digital Alpha VME 4/224 User Manual page 92

Interval Timer Tests
• Due to hardware limitations on interrupt detection, the value programmed
into timer 2 must be greater than 2.
• See the Intel 8254 interval timer sheet for more details.
Timer 1 Interrupt Test
This test verifies the interrupt path of timer 1 (periodic RT timer).
Timer 1 is programmed to mode 3, square wave mode. After the timer is initially
programmed to mode 3 and loaded with a count value, the OUT output is low
and remains low until the internal count value reaches zero. When the count
value reaches zero, OUT output is asserted high and remains high until timer 1
is reprogrammed.
A global interrupt count flag is checked verifying whether the interrupt service
routine was invoked.
Console Command: i8254_diag -t 6
4–14 Diagnostics