[PATCH v7 0/4] ECAP support on TI AM62x SoC

From: Julien Panis
Date: Wed Sep 21 2022 - 06:06:39 EST


The Enhanced Capture (ECAP) module can be used to timestamp events
detected on signal input pin. It can be used for time measurements
of pulse train signals.

ECAP module includes 4 timestamp capture registers. For all 4 sequenced
timestamp capture events (0->1->2->3->0->...), edge polarity (falling/rising
edge) can be selected.

This driver leverages counter subsystem to :
- select edge polarity for all 4 capture events (event mode)
- log timestamps for each capture event
Event polarity, and CAP0/1/2/3 timestamps give all the information
about the input pulse train. Further information can easily be computed :
period and/or duty cycle if frequency is constant, elapsed time between
pulses, etc...

Modifications since v6:
- Leverage counter array components (RFC PATCH v5)
- Remove the redundant doc of 'capture' items in sysfs-bus-counter ABI file
- Add driver info to MAINTAINERS file

Userspace commands :
### CLOCK SIGNAL ###
cd /sys/bus/counter/devices/counter0/signal0

# Get frequency
cat frequency

### INPUT SIGNAL ###
cd /sys/bus/counter/devices/counter0/signal1

# Get polarity for each capture event
cat polarity0
cat polarity1
cat polarity2
cat polarity3

# Set polarity for each capture event
echo positive > polarity0
echo negative > polarity1
echo positive > polarity2
echo negative > polarity3

### COUNT ###
cd /sys/bus/counter/devices/counter0/count0

# Get ceiling (counter max value)
cat ceiling

# Reset number of overflows & current timebase counter value
echo 0 > num_overflows
echo 0 > count

# Run ECAP
echo 1 > enable

# Get number of overflows & current timebase counter value
cat num_overflows
cat count

# Get captured timestamps
cat capture0
cat capture1
cat capture2
cat capture3

# Note that counter watches can also be used to get
# data from userspace application
# -> see tools/counter/counter_example.c

# Pause ECAP
echo 0 > enable

Julien Panis (4):
dt-bindings: counter: add ti,am62-ecap-capture.yaml
Documentation: ABI: sysfs-bus-counter: add frequency & num_overflows
items
counter: ti-ecap-capture: capture driver support for ECAP
MAINTAINERS: add TI ECAP driver info

Documentation/ABI/testing/sysfs-bus-counter | 14 +
.../counter/ti,am62-ecap-capture.yaml | 61 ++
MAINTAINERS | 6 +
drivers/counter/Kconfig | 15 +
drivers/counter/Makefile | 1 +
drivers/counter/ti-ecap-capture.c | 614 ++++++++++++++++++
6 files changed, 711 insertions(+)
create mode 100644 Documentation/devicetree/bindings/counter/ti,am62-ecap-capture.yaml
create mode 100644 drivers/counter/ti-ecap-capture.c

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