MOTOROLA
Chapter 11. System Interface Unit
11-23
Part III. Configuration
Table 11-13 describes SWSR Þelds.
11.8 The PowerPC Decrementer
A PowerPC-deÞned 32-bit decrementing counter supports the decrementer interrupt. In the
MPC860, the decrementer is clocked by TMBCLK, so TBSCR[TBE] must be set for the
decrementer to start. The timebase and decrementer counters are driven by TMBCLK:
The state of the decrementer is not affected by HRESET and SRESET, so it should be
initialized by software. Note, however, that it is disabled and reset by PORESET. It
continues counting while HRESET and SRESET are asserted and it is implemented with
the following requirements in mind.
¥
The decrementer is unaffected when read.
¥
When DEC[0] changes from 0 to 1, an interrupt request is signaled. If a previous
decrementer interrupt request was made, only one interrupt is reported.
¥
Explicitly changing DEC[0] from 0 to 1 in software signals an interrupt request.
A decrementer interrupt is also sent to the power-down wake-up logic, so the core can
waken from power-down mode. A decrementer exception causes a pending interrupt
request in the core, which is cleared automatically when the decrementer interrupt is taken,
Table 11-14 shows some decrementer periods available, assuming a 4-MHz oscillator.
11.8.1 Decrementer Register (DEC)
The decrementer register (DEC) is a PowerPC SPR. It can be read or written to by mfspr
or mtspr. DEC is powered by KAPWR and continues counting when KAPWR is applied.
Control of the decrementer is provided in the TBSCR. The decrementer and timebase use
TMBCLK. Note that DEC is a keyed register. It must be unlocked in TBK before it can be
written.
Table 11-13. SWSR Field Descriptions
Bits
Name
Description
0Ð15
SEQ
Sequence. This Þeld is the pattern that is used to control the state of the software watchdog timer.
Table 11-14. Decrementer Timeout Values
Count Value
Timeout
Count Value
Timeout
0
1
m
s
999999
1.0 s
9
10.
m
s
9999999
10.0 s
99
100.
m
s
99999999
100.0 s
999
1.0 ms
999999999
1000. s
9999
10.0 ms
FFFFFFFF (hex)
4295 s
T
dec
32
2
F
tmbclk
(
)
------------------------------
=
Содержание MPC860 PowerQUICC
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