ADSP-BF537 Blackfin Processor Hardware Reference
18-5
Real-Time Clock
Write
RTC_PREN
and then wait for the write complete event before pro-
gramming the other registers. It is safe to write
RTC_PREN
to 1 every time
the processor boots. The first time sets the bit, and subsequent writes have
no effect, as no state is changed.
L
Do not disable the prescaler by clearing the bit in
RTC_PREN
with-
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
RTC_PREN
and do not
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
RTC_PREN
to 0. The only reason to do so is to syn-
chronize the 1 Hz tick to a more precise external event, as the 1 Hz tick
predictably occurs a few
RTXI
cycles after a 0-to-1 transition of
RTC_PREN
.
Use the following sequence to achieve synchronization to within 100
μ
s.
1. Write
RTC_PREN
to 0.
2. Wait for the write to complete.
3. Wait for the external event.
4. Write
RTC_PREN
to 1.
5. Wait for the write to complete.
6. Reprogram the time into
RTC_STAT
.
Summary of Contents for Blackfin ADSP-BF537
Page 42: ...Contents xlii ADSP BF537 Blackfin Processor Hardware Reference ...
Page 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 138: ...Programming Examples 4 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 606: ...Programming Examples 9 94 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 660: ...Programming Examples 10 54 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 840: ...Programming Examples 13 42 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 876: ...Programming Examples 14 36 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 938: ...Programming Examples 15 62 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 958: ...Programming Examples 17 12 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 986: ...Programming Examples 18 28 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...