Intel
®
81341 and 81342 I/O Processors
December 2007
Developer’s Manual
Order Number: 315037-002US
807
Timers—Intel
®
81341 and 81342
12.0 Timers
This chapter describes the Intel XScale
®
processor dual-programmable 32-bit timers
and Watch Dog Timer. Topics include timer registers (TMRx, TCRx and TRRx), timer
operation, timer interrupts, and timer register values at initialization.
Each timer is programmed by the timer registers. These registers are mapped into Intel
XScale
®
processor Coprocessor 6, registers 0 to 8. They may be accessed/manipulated
with the MCR, MRC, STC, and LDC instructions. The CRn field of the instruction denotes
the register number to be accessed. The opcode_1 and opcode_2 fields of the
instruction should be zero. The CRm field of the instruction should be nine. Most
systems restrict access to CP6 to privileged processes. To control access to CP6, use
the Coprocessor Access Register.
shows a diagram of the timer functions. See also
for the
Programmable Timer state diagram.
When enabled, a timer decrements the user-defined count value with each Timer Clock
(TCLOCK) cycle. The countdown rate is also user-configurable to be equal to the
internal bus frequency, or the internal bus clock rate divided by 4, 8 or 16. The timers
can be programmed to either stop when the count value reaches zero (single-shot
mode) or run continuously (auto-reload mode). When a timer’s count reaches zero, the
timer’s interrupt unit signals the processor’s interrupt controller.
Figure 116. Programmable Timer Functional Diagram
A6769-01
Timer Mode Register
Timer Reload Register
32-Bit Register
Timer Count Register
32-Bit Register
32-Bit Compare
Against Zero
Interrupt Unit
Clock
Unit
Selected
Clock
Bus
Clock
Terminal Count
Address
Detect
Internal
CPU
Bus
Interrupt
Output
User/
Privileged Mode
Table 491. Timer Performance Ranges
Internal Bus Frequency (MHz)
Max Resolution (ns)
Max Range (mins)
400
2.5
2.86
