main.c

#include "driver/gpio.h"
#include "driver/i2c.h"
#include "esp_err.h"
#include "esp_log.h"
#include "freertos/task.h"

#include "sdkconfig.h" // generated by "make menuconfig"

#define SDA_PIN GPIO_NUM_15
#define SCL_PIN GPIO_NUM_2

#define tag "MAX44009"

#define MAX44009_ADDRESS1 0x4A
#define MAX44009_ADDRESS2 0x4B

#define I2C_MASTER_ACK 0
#define I2C_MASTER_NACK 1

void i2c_master_init()
{
	i2c_config_t i2c_config = {
		.mode = I2C_MODE_MASTER,
		.sda_io_num = SDA_PIN,
		.scl_io_num = SCL_PIN,
		.sda_pullup_en = GPIO_PULLUP_ENABLE,
		.scl_pullup_en = GPIO_PULLUP_ENABLE,
		.master.clk_speed = 400000
	};
	i2c_param_config(I2C_NUM_0, &i2c_config);
	i2c_driver_install(I2C_NUM_0, I2C_MODE_MASTER, 0, 0, 0);
}

void task_max44009_read_ambient_light(void *ignore)
{
	uint8_t lux_h;
	uint8_t lux_l;

	esp_err_t espErr;
	i2c_cmd_handle_t cmd;

	while (true) {
		vTaskDelay(800/portTICK_PERIOD_MS);

		cmd = i2c_cmd_link_create();
		i2c_master_start(cmd);
		i2c_master_write_byte(cmd, (MAX44009_ADDRESS1 << 1) | I2C_MASTER_WRITE, true);
		i2c_master_write_byte(cmd, 0x03, true);
		i2c_master_start(cmd);
		i2c_master_write_byte(cmd, (MAX44009_ADDRESS1 << 1) | I2C_MASTER_READ, true);
		i2c_master_read_byte(cmd, &lux_h, I2C_MASTER_NACK);
		i2c_master_stop(cmd);
		espErr = i2c_master_cmd_begin(I2C_NUM_0, cmd, 10/portTICK_PERIOD_MS);
		i2c_cmd_link_delete(cmd);
		// According to datasheet (p17), we can read two registers in one transmission
		// by repeated start signal. But unfortunately it timeouts.
		// So we re-create or I2C link for to get lux low-byte.
		cmd = i2c_cmd_link_create();
		i2c_master_start(cmd);
		i2c_master_write_byte(cmd, (MAX44009_ADDRESS1 << 1) | I2C_MASTER_WRITE, true);
		i2c_master_write_byte(cmd, 0x04, true);
		i2c_master_start(cmd);
		i2c_master_write_byte(cmd, (MAX44009_ADDRESS1 << 1) | I2C_MASTER_READ, true);
		i2c_master_read_byte(cmd, &lux_l, I2C_MASTER_NACK);
		i2c_master_stop(cmd);
		espErr = i2c_master_cmd_begin(I2C_NUM_0, cmd, 10/portTICK_PERIOD_MS);
		if (espErr == ESP_OK) {
			int exponent = (lux_h & 0xf0) >> 4;
			int mant = (lux_h & 0x0f) << 4 | lux_l;
			float lux = (float)(((0x00000001 << exponent) * (float)mant) * 0.045);
			ESP_LOGI(tag, "%.3f lux", lux);
		} else {
			ESP_LOGE(tag, "fail to read from sensor. code: %.2X", espErr);
		}

		i2c_cmd_link_delete(cmd);

	}
	vTaskDelete(NULL);
}

void app_main(void)
{
	i2c_master_init();
	xTaskCreate(&task_max44009_read_ambient_light, "max44009_read_ambient_light",  2048, NULL, 6, NULL);
}