Timer Facilities; Time Base; Figure 7-1. Relationship Of Timer Facilities To The Time Base - IBM PPC440X5 CPU Core User Manual

Preliminary

7. Timer Facilities

The PPC440x5 provides four timer facilities: a time base, a Decrementer (DEC), a Fixed Interval Timer (FIT),
and a Watchdog Timer. These facilities, which share the same source clock frequency, can support:
• Time-of-day functions
• General software timing functions
• Peripherals requiring periodic service
• General system maintenance
• System error recoverability
Figure 7-1 shows the relationship between these facilities and the clock source.

Figure 7-1. Relationship of Timer Facilities to the Time Base

7.1 Time Base

The time base is a 64-bit register which increments once during each period of the source clock, and provides
a time reference. Access to the time base is via two Special Purpose Registers (SPRs). The Time Base
Upper (TBU) SPR contains the high-order 32 bits of the time base, while the Time Base Lower (TBL) SPR
contains the low-order 32 bits.
timers.fm.
September 12, 2002
Time Base (Incrementer)
TBU (32 bits)
0 31
33
TBU (2 clocks)
31
29
TBL (2 clocks)
3
25
TBL (2 clocks)
7
21
TBL (2 clocks)
11
25
TBL (2 clocks)
7
21
TBL (2 clocks)
11
17
TBL (2 clocks)
15
13
TBL (2 clocks)
19
DEC (Decrementer)
(32 bits)
0
31
Zero Detect
TBL (32 bits)
31
0
Watchdog Timer
Period
Fixed Interval Timer
Period
Decrementer exception
User's Manual
PPC440x5 CPU Core
Reference
Clock
Source
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