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led_strip_spi.rst

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led_strip_spi - SPI-based driver for SK9822/APA102

Supported LEDs

The driver supports the following LEDs.

  • SK9822
  • APA102

Warning

The driver should work with APA102, but not tested.

Supported targets

The driver supports the following targets.

  • ESP32-family, including ESP32S2
  • ESP8266

Because the SPI driver in esp-idf differs from the one in ESP8266 RTOS SDK, the members of led_strip_spi_t — a descriptor to configure and manage LED strip — are different.

Note

If you have better ideas to unify the two structures, I would love to hear.

Usage

Call :cpp:func:`led_strip_spi_install()`.

#include <led_strip_spi.h>

ESP_ERROR_CHECK(led_strip_spi_install());

Create :cpp:type:`led_strip_spi_t` and initialize it with :c:macro:`LED_STRIP_SPI_DEFAULT()`.

led_strip_spi_t strip = LED_STRIP_SPI_DEFAULT();

Configure the LED strip descriptor. First, set length.

strip.length = N_PIXEL;

:cpp:type:`led_strip_spi_t` is an alias of either :cpp:struct:`led_strip_spi_esp32_t` or :cpp:struct:`led_strip_spi_esp8266_t`.

For ESP32, provide spi_device_handle_t, and set max_transfer_sz to the maximum size of the SPI data to transfer. :c:macro:`LED_STRIP_SPI_BUFFER_SIZE()` macro is provided to calculate the size from the number of pixels. Optionally, set SPI bus clock speed.

#if HELPER_TARGET_IS_ESP32
spi_device_handle_t device_handle;
strip.device_handle = device_handle;
strip.max_transfer_sz = LED_STRIP_SPI_BUFFER_SIZE(N_PIXEL);
strip.clock_speed_hz = 1000000 * 10;
#endif

Then, call :cpp:func:`led_strip_spi_init()`.

led_strip_spi_init(&strip);

The strip is now ready. Use :cpp:func:`led_strip_spi_set_pixel()` and other functions to modify the buffer. The buffer is sent to the bus when calling :c:func:`led_strip_spi_flush()`. See the example provided.

SPI signals and GPIO pins

The driver uses hardware SPI to drive LED strip. While ESP32-family chips can route SPI signals to GPIOs using GPIO matrix, ESP8266 cannot.

SPI clock speed

On ESP32, dedicated IO_MUX pins can clock faster (80Mhz) than GPIO pins through GPIO matrix (40Mhz), but the maximum clock frequency of SK9822 is 30Mhz, which is below the maximum clock frequency of GPIO matrix. As such, IO_MUX has no practical benefits here.

Known issues

SK9822 has bits to control global brightness, but the driver does not support it yet.

.. doxygengroup:: led_strip_spi_esp32
   :members:


.. doxygengroup:: led_strip_spi_esp8266
   :members:


.. doxygengroup:: led_strip_spi
   :members:


.. doxygengroup:: led_strip_spi_sk9822
   :members: