Motorola MPC8260 User Manual

13-24

MOTOROLA

The RISC timers can be used to track CP loading. The following sequence provides a way
to use the 16 RISC timers to determine if the CP ever exceeds the 96% utilization level
during any tick interval. Removing the timers adds a 4% margin to the CP utilization level,
but the aggressive user can use this technique to push CP performance to its limit. The user
should use the standard initialization sequence and incorporate the following differences:

1. Program the tick of the RISC timers to be every 1,024 x 16 = 16,384 system clocks. 

2. Disable RISC timer interrupts, if preferred. 

3. Using the 

SET

 

TIMER

 command, initialize all 16 RISC timers to have a timer period 

of 0xFFFF, which equates to 65,536.

4. Program one of the four general-purpose timers to increment once every tick. The 

general-purpose timer should be free-running and should have a timeout of 65,536.

5. After a few hours of operation, compare the general-purpose timer to the current 

count of RISC timer 15. If it is more than two ticks different from the 
general-purpose timer, the CP has, during some tick interval, exceeded the 96% 
utilization level.

General-purpose timers are up counters, but RISC timers are
down counters. The user should take this under consideration
when comparing timer counts.