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zephyr/samples/basic/blink_led
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Andrzej Głąbek 6e8132d1ae samples: blink_led: Fix the behavior of the sample 
Commit 16d8ce519c introduced changes
that caused this sample to no longer behave according to documentation
and for some hardware to no longer work at all.
On nRF51 SoCs for instance, the reported number of cycles per second
is 16M, what makes the calculated max_period and min_period to be 16
and 0 microseconds, respectively, what effectively makes it impossible
for the sample to return to the initial blinking frequency. Moreover,
with such short PWM periods, the blinking is not even noticeable.

This patch partially reverts the changes mentioned above, and instead
of calculating max_period and min_period basing on the reported clock
rate, it tries to only decrease the max_period if needed, accordingly
to what the used hardware can handle.
Documentation is also updated to mention the possible change in
observed behavior of the sample on some hardware.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>
2019-11-13 14:54:45 -06:00
..
src samples: blink_led: Fix the behavior of the sample 2019-11-13 14:54:45 -06:00
CMakeLists.txt license: cleanup: add SPDX Apache-2.0 license identifier 2019-04-07 08:45:22 -04:00
prj.conf driver: pwm: use new logger 2018-10-08 17:49:12 -04:00
README.rst samples: blink_led: Fix the behavior of the sample 2019-11-13 14:54:45 -06:00
sample.yaml sample/tests: replace DT_ define filters with dt_ functions 2019-11-04 09:02:14 -05:00

README.rst 

.. _blink-led-sample:

PWM: Blink LED
##############

Overview
********

This is a sample app which blinks a LED using PWM.

The LED will start at a blinking frequency of 1 Hz. Every 4 seconds,
the blinking frequency will double. When the blinking frequency
reaches 64 Hz, the blinking frequency will be halved every 4 seconds
until the blinking frequency reaches 1 Hz. This completes a whole
blinking cycle. This faster-then-slower LED blinking cycle repeats forever.

Since for some PWM hardware it might be not possible to set the PWM period of
1 second (to achieve the blinking frequency of 1 Hz), this application at its
beginning tries to determine what is available for the used PWM hardware,
and accordingly decreases the maximum PWM period (thus increases the initial
blinking frequency) if needed.


Wiring
******

Nucleo_F401RE, Nucleo_L476RG, STM32F4_DISCOVERY, Nucleo_F302R8
==============================================================
Connect PWM2(PA0) to LED

Nucleo_F103RB
=============
Connect PWM1(PA8) to LED

Nucleo_L496ZG
=============
No special board setup is necessary because there are three on-board LEDs (red,
green, blue) connected to the Nucleo's PWM.

Hexiwear K64
============
No special board setup is necessary because there is an on-board RGB LED
connected to the K64 PWM.

nrf52840_pca10056
=================
No special board setup is necessary because there is an on-board LED connected.

Building and Running
********************

This sample can be built for multiple boards, in this example we will build it
for the nrf52840_pca10056 board:

.. zephyr-app-commands::
   :zephyr-app: samples/basic/blink_led
   :board: nrf52840_pca10056
   :goals: build flash
   :compact:

After flashing the image to the board, the user LED on the board should start to
blinking as discussed in overview