pico-i2c-dma

A DMA based I2C driver for the RP2040.

Contents

• Installation
• Usage
• Examples
• API

Installation

Prerequisites

• 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

Usage

• 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

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)

API

The API is documented in i2c_dma.h