slave.c

#include <stdio.h>
#include "driver/i2c_slave.h"
#include "freertos/FreeRTOS.h"
#include "esp_log.h"
#include "esp_event.h"

static i2c_slave_dev_handle_t handle = 0;
static QueueHandle_t event_queue = 0;

enum {
    I2C_RECV = 0x1,
    I2C_REQ  = 0x2,
};

typedef struct {
    enum {
        i2c_txn_type_recv = 0,
        i2c_txn_type_req  = 1
    } type;

    union {
        struct {
            uint8_t buf[0x50];
            uint8_t len;
        } rx;
        i2c_slave_request_event_data_t tx;
    };
} i2c_txn_t;

bool i2c_slave_received(i2c_slave_dev_handle_t i2c_slave, const i2c_slave_rx_done_event_data_t *evt_data, void *arg) {
    BaseType_t xTaskWoken = 0;
    i2c_txn_t txn;
    txn.type = i2c_txn_type_recv;
    uint8_t maxsize = evt_data->length > sizeof(txn.rx.buf) ? sizeof(txn.rx.buf) : evt_data->length;
    txn.rx.len = maxsize;
    memcpy(txn.rx.buf, evt_data->buffer, maxsize);
    xQueueSendFromISR(event_queue, &txn, &xTaskWoken);
    return xTaskWoken;
}

bool i2c_slave_requested(i2c_slave_dev_handle_t i2c_slave, const i2c_slave_request_event_data_t *evt_data, void *arg) {
    BaseType_t xTaskWoken = 0;
    i2c_txn_t txn;
    txn.type = i2c_txn_type_req;
    xQueueSendFromISR(event_queue, &txn, &xTaskWoken);
    return xTaskWoken;
}

static void i2c_slave_task(void *arg) {
    while (1) {
        i2c_txn_t txn;
        if (xQueueReceive(event_queue, &txn, 10) == pdTRUE) {
            if (txn.type == i2c_txn_type_recv) {
                txn.rx.buf[txn.rx.len - 1] = 0;
                printf("received data: %s\n", (char *)txn.rx.buf);
            } else {
                printf("received read request, sending back test\n");
                uint32_t wlen = 0;
                ESP_ERROR_CHECK(i2c_slave_write(handle, (const uint8_t *)"testing", sizeof("testing"), &wlen, 100));
            }
        }
    }
    vTaskDelete(NULL);
}

void app_main(void)
{
    ESP_ERROR_CHECK(esp_event_loop_create_default());
    event_queue = xQueueCreate(16, sizeof(i2c_txn_t));
    if (!event_queue) {
        ESP_LOGE("i2cgdb", "failed to create queue");
        return;
    }
    i2c_slave_config_t cfg = {
        .i2c_port = 0,
        .scl_io_num = GPIO_NUM_15,
        .sda_io_num = GPIO_NUM_16,
        .clk_source = I2C_CLK_SRC_DEFAULT,
        .send_buf_depth = 100,
        .receive_buf_depth = 100,
        .slave_addr = 106,
        .addr_bit_len = I2C_ADDR_BIT_LEN_7,
    };

    ESP_ERROR_CHECK(i2c_new_slave_device(&cfg, &handle));

    i2c_slave_event_callbacks_t cbs = {
        .on_receive = &i2c_slave_received,
        .on_request = &i2c_slave_requested,
    };

    ESP_ERROR_CHECK(i2c_slave_register_event_callbacks(handle, &cbs, NULL));

    xTaskCreate(i2c_slave_task, "i2c_slave_task", 1024 * 4, NULL, 10, NULL);
}