apa102-gpiod 0.3.0

apa102 driver using userspace gpio character device through libgpiod

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.