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apa102 driver using userspace gpio character device through libgpiod

Project description

apa102_gpiod

A python library for accessing APA102 addressable LEDs using libgpiod, a library used to access the userspace gpio character device.

Useful for situations where you need to drive LEDs attached to non-SPI capable I/O lines, or when the in-kernel spi-gpio driver is not available (example: Pimoroni Blinkt on the default kernels from mainstream distributions)

The usage of this library is probably frowned upon by virture of linux/Documentation/driver-api/gpio/drivers-on-gpio.rst, so go and pressure the Raspberry Pi kernel devs to include spi-gpio, so we wouldn't have to resort to custom out-of-tree kernels or evil bitbanging in userspace!

Prerequisites

  • Linux Kernel >= 4.8
  • libgpiod >= 039b301b173c78664775d1ea93493825ef80c9d4
  • Python >= 3.6

Installation

  • libgpiod
    • https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/
    • Remember to --enable-bindings-python when configuring.
  • apa102_gpiod
    • pip install apa102_gpiod

Tests

  • Tests can be found in the test directory.
    • Only unit tests are present now, more tests welcome.
  • Use your favourite test runner to run the tests, or:
    • pip install setuptools
    • pip install pytest
    • python setup.py test

Performance

Since we're accessing the GPIOs through the character device and not through some memory-mapped magic, performance is guaranteed to be lower. Here are some test results:

Device Software Achieved data rate (kByte/s)
RPI3 B Arch Linux ARM Linux 4.14.37 13962

Caveats

  • No clock rate control is implemented, since the achieved data rates are way below the maximum data rates supported by the APA102.
    • File an issue report if needed.

Examples

See the examples directory.

Licensing

This project is licensed under the MIT License. See LICENSE.txt for more details.

Project details


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