Motorola MPC860 PowerQUICC, User Manual

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MOTOROLA Chapter 19. Communications Processor 19-17
Part V. The Communications Processor Module
As an example, the following sequence demonstrates how RISC timer 0 is initialized to
generate an interrupt approximately every second using a 25-MHz general system clock:
1. Write RCCR[TIMEP] with 0b111111 to generate the slowest timer. This value
generates a table scan tick every 65,536 clocks, which is every 2.6 ms at 25 MHz.
2. ConÞgure TM_BASE to point to a location in the dual-port RAM with 4 bytes
available. Assuming that the beginning of dual-port RAM is available, write 0x0000
to TM_BASE.
3. Write 0x0000 to TM_CNT to see how many ticks have elapsed since the CP internal
timer was enabled (optional).
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 CPM interrupt mask register so the RISC timers will
generate a system interrupt. Initialize the CPM interrupt conÞguration register.
7. Write 0xC000_0EE6 to TM_CMD. This enables RISC timer 0 to timeout after 3,814
(decimal) ticks. The timer automatically restarts after it times out.
8. Write 0x0851 to the CPCR to issue
SET TIMER
.
9. Set RCCR[TIME] to start RISC timer table scanning.
19.7.7 RISC Timer Interrupt Handling
The following sequence shows what normally occurs within an interrupt handler for the
RISC timer table:
1. Once an interrupt occurs, read the RTER to see which timers have caused interrupts.
The RISC timer event bits are usually cleared at this time.
2. Issue any additional
SET TIMER
commands now or later, as preferred. Nothing needs
to be done if the timer is automatically being restarted for repetitive interrupts.
3. Clear CISR[RTT].
4. Execute the rÞ instruction.
19.7.8 Using the RISC Timers to Track CP Loading
The RISC timers can be used to track CP loading. The following sequence is a method for
using the 16 RISC timers to determine if the CP ever exceeds the 96% utilization level
during a scan tick interval. Removing the timers adds a 4% margin to the CPÕs utilization
level, but an aggressive user can use this technique to push the CP performance to its limit.
Incorporate the following steps to the standard initialization sequence:
1. Program RCCR[TIMEP] to 0b001111 for a table scan tick of 16
´
(1,024) = 16,384.
2. Disable RISC timer table interrupts, if preferred.
3. Using
SET TIMER
, initialize all 16 RISC timers to have a timer period of 0x0000,
which corresponds to 65,536.