Analog Devices Blackfin ADSP-BF537 Hardware Reference Manual page 963

Write
RTC_PREN
gramming the other registers. It is safe to write
the processor boots. The first time sets the bit, and subsequent writes have
no effect, as no state is changed.
Do not disable the prescaler by clearing the bit in
out making sure that there are no writes to RTC MMRs in
progress. Do not switch between fast and slow mode during normal
operation by setting and clearing this bit, as this disrupts the accu-
rate tracking of real time by the counters. To avoid these potential
errors, initialize the RTC during startup via
dynamically alter the state of the prescaler during normal
operation.
Running without the prescaler enabled is provided primarily as a test
mode. All functionality works, just 32,768 times as fast. Typical software
should never program
chronize the 1 Hz tick to a more precise external event, as the 1 Hz tick
predictably occurs a few
Use the following sequence to achieve synchronization to within 100 μs.
1. Write
RTC_PREN
2. Wait for the write to complete.
3. Wait for the external event.
4. Write
RTC_PREN
5. Wait for the write to complete.
6. Reprogram the time into
ADSP-BF537 Blackfin Processor Hardware Reference
and then wait for the write complete event before pro-
to 0. The only reason to do so is to syn-
RTC_PREN
cycles after a 0-to-1 transition of
RTXI
to 0.
to 1.
RTC_STAT
Real-Time Clock
to 1 every time
RTC_PREN
RTC_PREN
RTC_PREN
.
with-
and do not
.
RTC_PREN
18-5