Motorola MPC8260 - Manual (Page 453)

MOTOROLA Chapter 13. Communications Processor Module Overview 13-23
Part IV. Communications Processor Module
3. (Optional) Write 0x0000 to the TM_CNT Þeld in the RISC timer table parameter
RAM to see how many ticks elapsed since the RISC internal timer was enabled.
4. Write 0xFFFF to the RTER to clear any previous events.
5. Write 0x0001 to the RTMR to enable RISC timer 0 to generate an interrupt.
6. Write 0x0002_0000 to the SIU interrupt mask register (SIMR_L) to allow the RISC
timers to generate a system interrupt. Initialize the SIU interrupt conÞguration
register.
7. Write 0xC000_080D to the TM_CMD Þeld of the RISC timer table parameter
RAM. This enables RISC timer 0 to timeout after 2,061(decimal) ticks of the timer.
The timer automatically restarts after it times out.
8. Write 0x29E1_0008 to the CPCR to issue the SET TIMER command.
9. Set RCCR[TIME] to enable the RISC timer to begin operation.
13.6.8 RISC Timer Interrupt Handling
The following sequence describes what normally would occur within an interrupt handler
for the RISC timer tables:
1. Once an interrupt occurs, read RTER to see which timers have caused interrupts. The
RISC timer event bits are usually cleared by this time.
2. Issue additional SET TIMER commands at this time or later, as preferred. Nothing
needs to be done if the timer is being automatically restarted for a repetitive
interrupt.
3. Clear the RTT bit in the SIU interrupt pending register (SIPNR_L).
4. Execute the RTE instruction.
13.6.9 RISC Timer Table Scan Algorithm
The CP scans the timer table once every tick. It handles each of the 16 timers at its turn and
checks for other requests with higher priority to service, before handling the next one. For
each valid timer in the table, the CP decrements the count and checks for a timeout. If none
occurs, the CP moves to the next timer. If a timeout occurs, the CP sets the corresponding
event bit in RTER. Then the CP checks to see if the timer is to be restarted and if it is, the
CP leaves the timerÕs valid bit set in the R_TMV location and resets the current count to the
initial count. Otherwise, it clears R_TMV. Once the timer table scanning has completed, the
CP updates the TM_CNT value in the RISC timer table parameter RAM and stops working
on the timer tables until the next tick.
If a SET TIMER command is issued, the CP makes the appropriate modiÞcations to the timer
table and parameter RAM, but does not scan the timer table until the next tick of the internal
timer. It is important to use the
SET TIMER command to properly synchronize timer table
modiÞcations to the execution of the CP.