Register Model
e200z3 Power Architecture Core Reference Manual, Rev. 2
Freescale Semiconductor
2-29
•
The TB is a long-period counter driven at an implementation-dependent frequency.
•
The decrementer, updated at the same rate as the TB, signals an exception after a specified period
unless one of the following occurs:
— Software alters DEC in the interim.
— The TB update frequency changes.
The DEC is typically used as a general-purpose software timer.
•
The time base for the TB and DEC is selected by the time base enable (TBEN) and select time base
clock (SEL_TBCLK) bits in HID0, as follows:
— If HID0[TBEN] = 1 and HID0[SEL_TBCLK] = 0, the time base and decrementer are based on
processor clock.
— If HID0[TBEN] = 1 and HID0[SEL_TBCLK] = 1, the time base and decrementer are based on
the p_tbclk input.
•
Software can select one from of four TB bits to signal a fixed-interval interrupt when the bit
transitions from 0 to 1. It typically triggers periodic system maintenance functions. Bits that can be
selected are implementation-dependent.
•
The watchdog timer, also a selected TB bit, signals a critical exception when the selected bit
transitions from 0 to 1. It is typically used for system error recovery. If software does not respond
in time to the initial interrupt by clearing the associated status bits in the TSR before the next
expiration of the watchdog timer interval, a watchdog timer-generated processor reset may result,
if so enabled.
All timer facilities must be initialized during start-up.
2.11.1
Timer Control Register (TCR)
TCR, shown in
, provides control information for the CPU timer facilities. The EREF describes
the TCR in detail. TCR[WRC] functions are implementation-dependent. In addition, the core implements
two implementation-specific fields, TCR[WPEXT] and TCR[FPEXT].
32 33 34 35
36
37
38 39
40
41
42 43
46 47
50 51
63
Field WP WRC WIE DIE
FP
FIE ARE —
WPEXT
FPEXT
—
Reset
All zeros
R/W
R/W
SPR
SPR 340
Figure 2-24. Timer Control Register (TCR)
Содержание e200z3
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