Intel PXA26X - Manual (Page 143)

Intel® PXA26x Processor Family Developer’s Manual 4-35
System Integration Unit
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 4-42 shows the bitmap of the RTC Status Register.
4.3.3 Trim Procedure
The Hz clock driving the RTC is generated by dividing the output of the oscillator multiplexor. The
inherent inaccuracies of crystals, aggravated by varying capacitance of the board connections, as
well as other variables, may cause the time base to be somewhat inaccurate. This requires a slight
adjustment in the desired clock period. The processor, through the RTTR, lets you adjust (or trim)
the Hz-time base to an error of less than 1 ppm. Such that if the Hz clock is set to be 1 Hz, there
would be an error of less than 5 seconds per month.
The RTTR is reset to its default value of 0x0000_7FFF each time the nRESET signal is asserted.
This yields approximately a 1 Hz clock.
When the clock divisor count (RTTR[15:0]) is set to 0x0, the Hz clock feeding the RTC maintains
a high level signal - essentially disabling the RTC. For all non-zero values programmed into the
clock divisor count, the Hz-clock frequency will be the 32-KHz-clock source divided by the clock
divisor count plus 1.
Table 4-42. RTSR Bit Definitions
Physical Address
0x4090_0008
RTSR 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
HZ
E
AL
E
HZ AL
Reset ? ? ? ? ? ? ? ? ? ? ? ? / ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 0 0 0 0
Bits Name Description
<31:4> — Reserved
<3> HZE
HZ INTERRUPT ENABLE:
0 – The HZ interrupt is not enabled.
1 – The HZ interrupt is enabled.
<2> ALE
RTC ALARM INTERRUPT ENABLE:
0 – The RTC alarm interrupt is not enabled.
1 – The RTC alarm interrupt is enabled.
<1> HZ
HZ RISING-EDGE DETECTED:
0 – No rising edge has been detected.
1 – A rising edge has been detected and HZE bit is set.
<0> AL
RTC ALARM DETECTED:
0 – No RTC alarm has been detected.
1 – An RTC alarm has been detected (RTNR matches RCAR).and ALE bit is set