A DMA based I2C driver for the RP2040.

• Installation
• Usage
• Examples
• API

• The Raspberry Pi Pico SDK has been successfully installed and the PICO_SDK_PATH environment variable has been appropriately set
• The FreeRTOS Kernel has been successfully installed and the FREERTOS_KERNEL_PATH environment variable has been appropriately set

If the Prerequisites are satisfied, this repository can be cloned and built with the following commands:

git clone https://github.com/fivdi/pico-i2c-dma.git
cd pico-i2c-dma
mkdir build
cd build
cmake ..
make

• Call i2c_dma_init to initialize an I2C peripheral, its baudrate, its SDA pin, its SCL pin, to enable the peripheral, and to prepare it for DMA usage
• Call i2c_dma_* functions to communicate with I2C devices on an I2C bus

Here is a minimalistic example that continuously reads the temperature from an MCP9808 temperature sensor and prints the temperature.

#include "FreeRTOS.h"
#include "task.h"
#include "pico/stdlib.h"
#include "i2c_dma.h"
#include "mprintf.h"

static const uint8_t MCP9808_ADDR = 0x18;
static const uint8_t MCP9808_TEMP_REG = 0x05;
static const int32_t MCP9808_POWER_UP_DELAY_MS = 300;

static void mcp9808_task(void *args) {
  i2c_dma_t *i2c_dma;
  i2c_dma_init(&i2c_dma, i2c0, (1000 * 1000), 4, 5);

  vTaskDelay(pdMS_TO_TICKS(MCP9808_POWER_UP_DELAY_MS));

  while (true) {
    uint16_t raw_temp;
    i2c_dma_read_word_swapped(
      i2c_dma, MCP9808_ADDR, MCP9808_TEMP_REG, &raw_temp
    );

    double temp = (raw_temp & 0x0fff) / 16.0 - (raw_temp & 0x1000 ? 256 : 0);

    mprintf("temp: %.4f\n", temp);

    vTaskDelay(pdMS_TO_TICKS(1000));
  }
}

int main(void) {
  stdio_init_all();

  xTaskCreate(
    mcp9808_task, "mcp9808-task", configMINIMAL_STACK_SIZE,
    NULL, configMAX_PRIORITIES - 2, NULL
  );

  vTaskStartScheduler();
}

Examples can be found in the examples directory. The examples were implemented to verify that the I2C driver functions as expected rather than to do anything useful. Each example has a readme explaining its purpose.

Depending on the example, one or more of the following I2C devices will be required for the example to function as expected:

• An MCP9808 temperature sensor at address 0x18 on I2C0 (GP4 and GP5)
• A 128x64 pixel SSD1306 OLED display at address 0x3c on I2C0 (GP4 and GP5)
• An MCP9808 temperature sensor at address 0x18 on I2C1 (GP6 and GP7)
• A BME280 sensor at address 0x76 on I2C1 (GP6 and GP7)

The API is documented in i2c_dma.h