
Hawk PCI Host Bridge & Multi-Processor Interrupt Controller
MVME5100 Single Board Computer Programmer’s Reference (6806800H17B
)
102
Each timer is composed of a prescaler and a counter. The prescaler determines the resolution
of the timer, and is programmable to any binary value between 1 microseconds and 32,768
microsecons. The counter counts in the units provided by the prescaler. For example, the
watchdog timer would reach a count of zero within 24 microseconds if the prescaler was
programmed to 2 microseconds and the counter was programmed to 12.
The watchdog timers are controlled by registers mapped within the PPC control register space.
Each timer has a WDTxCNTL register and a WDTxSTAT register. The WDTxCNTL register can be
used to start or stop the timer, write a new reload value into the timer, or cause the timer to
initialize itself to a previously written reload value. The WDTxSTAT register is used to read the
instantaneous count value of the watchdog timer.
Programming the Watchdog Timers
To program the Watchdog Timers through the WDTxCNTL register,
1. ‘Arm’ the WDTxCNTL register by writing PATTERN_1 into the KEY field.
Only the KEY byte lane may be selected during this process. The WDTxCNTL register will not
arm itself if any of the other byte lanes are selected or the KEY field is written with any other
value than PATTERN_1.
The operation of the timer itself remains unaffected by this write.
2. Write the new programming information to the WDTxCNTL register.
The KEY field byte lane must be selected and must be written with PATTERN_2 for the write
to take affect. The effects on the WDTxCNTL register depend on the byte lanes that are
written to during step 2 and are shown in following table.
Table 2-18 WDTxCNTL Programming
Byte Lane Selection
Results
KEY
ENAB
/RES
RELOAD
WDT
WDTxCNTL Register
0:7
8:15
16:23
24:31
Prescaler/
Enable
Counter
RES/ENAB
RELOAD
No
x
x
x
No Change
No Change
No Change
No Change
Yes
No
x x Update
from
RES/ENAB
Update
from
RELOAD
No Change
No Change
Содержание MVME5100
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