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Intel® PXA255 Processor Developer’s Manual 4-37
System Integration Unit
4.4.2.3 OS Timer Watchdog Match Enable Register (OWER)
The OWER, shown in Table 4-43, contains a single control bit (bit 0) that enables the watchdog
function. This bit is set by writing a one to it and can only be cleared by one of the reset functions
such as, hardware reset, sleep reset, watchdog reset, and GPIO reset.
4.4.2.4 OS Timer Count Register (OSCR)
The OSCR, shown in Table 4-44, is a 32-bit counter that increments on rising edges of the
3.6864 MHz clock. This counter can be read or written at any time. It is recommended that the
system write-protect this register through the MMU protection mechanisms.
After the OSCR is written, there is a delay before the register is actually updated. Software must
make sure the register has changed to the new value before relying on the contents of the register.
4.4.2.5 OS Timer Status Register (OSSR)
The OSSR, shown in Table 4-45, contains status bits that indicate a match has occurred between
any of the four match registers and the OSCR. These bits are set when the match event occurs
(following the rising edge of the 3.6864 MHz clock) and the corresponding interrupt enable bit is
set in the OIER. The OSSR bits are cleared by writing a one to the proper bit position. Writing
zeros to this register has no effect. Write all reserved bits as zeros and ignore all reads.
Table 4-43. OWER Bit Definitions
Physical Address
0x40A0_0018
OS Timer Watchdog Match Enable
Register (OWER)
System Integration Unit
Bit
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
reserved
WME
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Bits Name Description
<31:1> — reserved
<0> WME
Watchdog Match Enable
0 – OSMR3 match will NOT cause a reset of the processor
1 – OSMR3 match causes a reset of the processor.
Table 4-44. OSCR Bit Definitions
Physical Address
0x40A0_0010
OS Timer Count Register (OSCR) System Integration Unit
Bit
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
OSCV
Reset
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Bits Name Description
<31:0> OSCV
OS Timer Counter Value.
The current value of the OS timer counter.