Filter
Top Products
Intel® PXA255 Processor Developer’s Manual 4-31
System Integration Unit
4.3.2.3 RTC Counter Register (RCNR)
The RCNR, shown in Table 4-39, is a read/write register. The counter may be written by the
processor at any time although it is recommended that the operating system prevent inadvertent
writes to the RCNR through the use of the MMU protection mechanisms (refer to the Intel®
XScale™ Microarchitecture for the Intel® PXA255 Processor User’s Manual for details of MMU
operation.)
Because of the asynchronous nature of the HZ clock relative to the processor clock, writes to this
counter are controlled by a hardware mechanism that delays the actual write to the counter after the
processor store is performed by approximately two 32 kHz clock cycles. In case of multiple writes
to RCNR in quick succession, the final update to the RCNR counter may be delayed by up to two
32 kHz clock cycles.
The RCNR may be read at any time. Reads reflect the value in the counter after it increments or has
been written and does not have the two 32 kHz clock cycle delay.
4.3.2.4 RTC Status Register (RTSR)
The RTSR, shown in Table 4-40, is cleared to all zeroes at hardware reset. The ALE and HZE bits
enable both the interrupt for the functions as well as the updating the AL and HZ bits. The AL and
HZ bits are status bits and are set by the RTC logic if the ALE and HZE bits are set respectively.
They are cleared by writing ones to the AL and HZ bits. The AL and HZ bits are routed to the
interrupt controller where they may be enabled to cause a first level interrupt. Write zeros to all
reserved bits and ignore all reads to the reserved bits.
In Sleep mode, only AL events set the status bit in the RTSR register. The HZ bit is not set in Sleep
mode since it is a recurring event.
Table 4-40 shows the bitmap of the RTC Status Register.
Table 4-39. RCNR Bit Definitions
Physical Address
0x4090_0000
RCNR 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
RCV
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> RCV
RTC Count Value.
The current value of the RTC counter.