IBM PowerPC 405GP

Chapter 11. Timer Facilities
The PPC405GP provides four timer facilities: a time base, a Programmable Interval Timer (PIT), a
fixed
interval timer (FIT), and a watchdog timer. The PIT is a Special Purpose Register (SPR). These
facilities, which are driven by the same base clock, can, among other things, be used for:
• Time-of-day functions
• Data logging functions
• Peripherals requiring periodic service
• Periodic task switching
Additionally, the watchdog timer can help a system to recover from faulty hardware or software.
Figure
11-1 shows the relationship of the timers and the clock source to the time base.
]=0
CPCO_CR1 [CETE
CPU Clock -~,
I
\
TmrClk ---'-
CPCO_CR1 [CETE]
= 1
Time Base (Incrementer)
TBl (32 bits)
TBU (32 bits)
:':> 0
31
-
[> 0
31
I
. - ..........
- - -
--------------------------
-Bit3
(2
29
clocks)
- Bit? (2
25
clocks)
- Bit 11 (2
21
clocks)
} Watchdo
9 Timer Events
- Bit 15 (2
17
clocks)
r- Bit 11
(221 clocks)
} FITEve~ts
I- Bit 15
(2
17
clocks)
r- Bit 19
(2
13
clocks)
'- Bit 23 (2
9
clocks)
PIT (Decrementer)
(32
bits)
-
[>0
31
L
Zero Detect } PIT Events
Figure 11-1. Relationship of Timer Facilities to the Time Base
Preliminary
Timer Facilities
11-1