Modes of Operation
15-28
ADSP-BF537 Blackfin Processor Hardware Reference
The
PERIOD_CNT
bit in the
TIMERx_CONFIG
register controls the point in
time at which this set of transactions is executed. Taken together, these
three events are called a measurement report. The
TOVF_ERRx
bit does not
get set at a measurement report. A measurement report occurs at most
once per input signal period.
The current timer counter value is always copied to the width buffer and
period buffer registers at the trailing and leading edges of the input signal,
respectively, but these values are not visible to software. A measurement
report event samples the captured values into visible registers and sets the
timer interrupt to signal that
TIMERx_PERIOD
and
TIMERx_WIDTH
are ready
to be read. When the
PERIOD_CNT
bit is set, the measurement report occurs
just after the period buffer register captures its value (at a leading edge).
When the
PERIOD_CNT
bit is cleared, the measurement report occurs just
after the width buffer register captures its value (at a trailing edge).
If the
PERIOD_CNT
bit is set and a leading edge occurred (see
then the
TIMERx_PERIOD
and
TIMERx_WIDTH
registers report the pulse
period and pulse width measured in the period that just ended. If the
PERIOD_CNT
bit is cleared and a trailing edge occurred (see
),
then the
TIMERx_WIDTH
register reports the pulse width measured in the
pulse that just ended, but the
TIMERx_PERIOD
register reports the pulse
period measured at the end of the previous period.
If the
PERIOD_CNT
bit is cleared and the first trailing edge occurred, then
the first period value has not yet been measured at the first measurement
report, so the period value is not valid. Reading the
TIMERx_PERIOD
value
in this case returns 0, as shown in
width of a waveform that has only one leading edge and one trailing edge,
set
PERIOD_CNT
=
0
. If
PERIOD_CNT
=
1
for this case, no period value is cap-
tured in the period buffer register. Instead, an error report interrupt is
generated (if enabled) when the counter range is exceeded and the counter
wraps around. In this case, both
TIMERx_WIDTH
and
TIMERx_PERIOD
read 0
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 ...