text: #include <stdio.h>
  #include <string.h>
  
  #include "sdkconfig.h"
  #include "esp_log.h"
  
  #include "freertos/FreeRTOS.h"
  #include "freertos/task.h"
  
  #include "u8g2_esp32_hal.h"
  
  static const char *TAG = "u8g2_hal";
  static const unsigned int I2C_TIMEOUT_MS = 1000;
  
  static spi_device_handle_t handle_spi;      // SPI handle.
  static i2c_cmd_handle_t    handle_i2c;      // I2C handle.
  static u8g2_esp32_hal_t    u8g2_esp32_hal;  // HAL state data.
  
  #undef ESP_ERROR_CHECK
  #define ESP_ERROR_CHECK(x)   do { esp_err_t rc = (x); if (rc != ESP_OK) { ESP_LOGE("err", "esp_err_t = %d", rc); assert(0 && #x);} } while(0);
  
  /*
   * Initialze the ESP32 HAL.
   */
  void u8g2_esp32_hal_init(u8g2_esp32_hal_t u8g2_esp32_hal_param) {
  	u8g2_esp32_hal = u8g2_esp32_hal_param;
  } // u8g2_esp32_hal_init
  
  /*
   * HAL callback function as prescribed by the U8G2 library.  This callback is invoked
   * to handle SPI communications.
   */
  uint8_t u8g2_esp32_spi_byte_cb(u8x8_t *u8x8, uint8_t msg, uint8_t arg_int, void *arg_ptr) {
  	ESP_LOGD(TAG, "spi_byte_cb: Received a msg: %d, arg_int: %d, arg_ptr: %p", msg, arg_int, arg_ptr);
  	switch(msg) {
  		case U8X8_MSG_BYTE_SET_DC:
  			if (u8g2_esp32_hal.dc != U8G2_ESP32_HAL_UNDEFINED) {
  				gpio_set_level(u8g2_esp32_hal.dc, arg_int);
  			}
  			break;
  
  		case U8X8_MSG_BYTE_INIT: {
  			if (u8g2_esp32_hal.clk == U8G2_ESP32_HAL_UNDEFINED ||
  					u8g2_esp32_hal.mosi == U8G2_ESP32_HAL_UNDEFINED ||
  					u8g2_esp32_hal.cs == U8G2_ESP32_HAL_UNDEFINED) {
  				break;
  			}
  
  		  spi_bus_config_t bus_config;
                    memset(&bus_config, 0, sizeof(spi_bus_config_t));
  		  bus_config.sclk_io_num   = u8g2_esp32_hal.clk; // CLK
  		  bus_config.mosi_io_num   = u8g2_esp32_hal.mosi; // MOSI
  		  bus_config.miso_io_num   = -1; // MISO
  		  bus_config.quadwp_io_num = -1; // Not used
  		  bus_config.quadhd_io_num = -1; // Not used
  		  //ESP_LOGI(TAG, "... Initializing bus.");
  		  ESP_ERROR_CHECK(spi_bus_initialize(HSPI_HOST, &bus_config, 1));
  
  		  spi_device_interface_config_t dev_config;
  		  dev_config.address_bits     = 0;
  		  dev_config.command_bits     = 0;
  		  dev_config.dummy_bits       = 0;
  		  dev_config.mode             = 0;
  		  dev_config.duty_cycle_pos   = 0;
  		  dev_config.cs_ena_posttrans = 0;
  		  dev_config.cs_ena_pretrans  = 0;
  		  dev_config.clock_speed_hz   = 10000;
  		  dev_config.spics_io_num     = u8g2_esp32_hal.cs;
  		  dev_config.flags            = 0;
  		  dev_config.queue_size       = 200;
  		  dev_config.pre_cb           = NULL;
  		  dev_config.post_cb          = NULL;
  		  //ESP_LOGI(TAG, "... Adding device bus.");
  		  ESP_ERROR_CHECK(spi_bus_add_device(HSPI_HOST, &dev_config, &handle_spi));
  
  		  break;
  		}
  
  		case U8X8_MSG_BYTE_SEND: {
  			spi_transaction_t trans_desc;
  			trans_desc.addr      = 0;
  			trans_desc.cmd   	 = 0;
  			trans_desc.flags     = 0;
  			trans_desc.length    = 8 * arg_int; // Number of bits NOT number of bytes.
  			trans_desc.rxlength  = 0;
  			trans_desc.tx_buffer = arg_ptr;
  			trans_desc.rx_buffer = NULL;
  
  			//ESP_LOGI(TAG, "... Transmitting %d bytes.", arg_int);
  			ESP_ERROR_CHECK(spi_device_transmit(handle_spi, &trans_desc));
  			break;
  		}
  	}
  	return 0;
  } // u8g2_esp32_spi_byte_cb
  
  /*
   * HAL callback function as prescribed by the U8G2 library.  This callback is invoked
   * to handle I2C communications.
   */
  uint8_t u8g2_esp32_i2c_byte_cb(u8x8_t *u8x8, uint8_t msg, uint8_t arg_int, void *arg_ptr) {
  	ESP_LOGD(TAG, "i2c_cb: Received a msg: %d, arg_int: %d, arg_ptr: %p", msg, arg_int, arg_ptr);
  
  	switch(msg) {
  		case U8X8_MSG_BYTE_SET_DC: {
  			if (u8g2_esp32_hal.dc != U8G2_ESP32_HAL_UNDEFINED) {
  				gpio_set_level(u8g2_esp32_hal.dc, arg_int);
  			}
  			break;
  		}
  
  		case U8X8_MSG_BYTE_INIT: {
  			if (u8g2_esp32_hal.sda == U8G2_ESP32_HAL_UNDEFINED ||
  					u8g2_esp32_hal.scl == U8G2_ESP32_HAL_UNDEFINED) {
  				break;
  			}
  
  		    i2c_config_t conf;
              memset(&conf, 0, sizeof(i2c_config_t));
  		    conf.mode = I2C_MODE_MASTER;
  			ESP_LOGI(TAG, "sda_io_num %d", u8g2_esp32_hal.sda);
  		    conf.sda_io_num = u8g2_esp32_hal.sda;
  		    conf.sda_pullup_en = GPIO_PULLUP_ENABLE;
  			ESP_LOGI(TAG, "scl_io_num %d", u8g2_esp32_hal.scl);
  		    conf.scl_io_num = u8g2_esp32_hal.scl;
  		    conf.scl_pullup_en = GPIO_PULLUP_ENABLE;
  			ESP_LOGI(TAG, "clk_speed %d", I2C_MASTER_FREQ_HZ);
  		    conf.master.clk_speed = I2C_MASTER_FREQ_HZ;
  			ESP_LOGI(TAG, "i2c_param_config %d", conf.mode);
  		    ESP_ERROR_CHECK(i2c_param_config(I2C_MASTER_NUM, &conf));
  			ESP_LOGI(TAG, "i2c_driver_install %d", I2C_MASTER_NUM);
  		    ESP_ERROR_CHECK(i2c_driver_install(I2C_MASTER_NUM, conf.mode, I2C_MASTER_RX_BUF_DISABLE, I2C_MASTER_TX_BUF_DISABLE, 0));
  			break;
  		}
  
  		case U8X8_MSG_BYTE_SEND: {
  			uint8_t* data_ptr = (uint8_t*)arg_ptr;
  			ESP_LOG_BUFFER_HEXDUMP(TAG, data_ptr, arg_int, ESP_LOG_VERBOSE);
  
  			while( arg_int > 0 ) {
  			   ESP_ERROR_CHECK(i2c_master_write_byte(handle_i2c, *data_ptr, ACK_CHECK_EN));
  			   data_ptr++;
  			   arg_int--;
  			}
  			break;
  		}
  
  		case U8X8_MSG_BYTE_START_TRANSFER: {
  			uint8_t i2c_address = u8x8_GetI2CAddress(u8x8);
  			handle_i2c = i2c_cmd_link_create();
  			ESP_LOGD(TAG, "Start I2C transfer to %02X.", i2c_address>>1);
  			ESP_ERROR_CHECK(i2c_master_start(handle_i2c));
  			ESP_ERROR_CHECK(i2c_master_write_byte(handle_i2c, i2c_address | I2C_MASTER_WRITE, ACK_CHECK_EN));
  			break;
  		}
  
  		case U8X8_MSG_BYTE_END_TRANSFER: {
  			ESP_LOGD(TAG, "End I2C transfer.");
  			ESP_ERROR_CHECK(i2c_master_stop(handle_i2c));
  			ESP_ERROR_CHECK(i2c_master_cmd_begin(I2C_MASTER_NUM, handle_i2c, I2C_TIMEOUT_MS / portTICK_RATE_MS));
  			i2c_cmd_link_delete(handle_i2c);
  			break;
  		}
  	}
  	return 0;
  } // u8g2_esp32_i2c_byte_cb
  
  /*
   * HAL callback function as prescribed by the U8G2 library.  This callback is invoked
   * to handle callbacks for GPIO and delay functions.
   */
  uint8_t u8g2_esp32_gpio_and_delay_cb(u8x8_t *u8x8, uint8_t msg, uint8_t arg_int, void *arg_ptr) {
  	ESP_LOGD(TAG, "gpio_and_delay_cb: Received a msg: %d, arg_int: %d, arg_ptr: %p", msg, arg_int, arg_ptr);
  
  	switch(msg) {
  	// Initialize the GPIO and DELAY HAL functions.  If the pins for DC and RESET have been
  	// specified then we define those pins as GPIO outputs.
  		case U8X8_MSG_GPIO_AND_DELAY_INIT: {
  			uint64_t bitmask = 0;
  			if (u8g2_esp32_hal.dc != U8G2_ESP32_HAL_UNDEFINED) {
  				bitmask = bitmask | (1ull<<u8g2_esp32_hal.dc);
  			}
  			if (u8g2_esp32_hal.reset != U8G2_ESP32_HAL_UNDEFINED) {
  				bitmask = bitmask | (1ull<<u8g2_esp32_hal.reset);
  			}
  			if (u8g2_esp32_hal.cs != U8G2_ESP32_HAL_UNDEFINED) {
  				bitmask = bitmask | (1ull<<u8g2_esp32_hal.cs);
  			}
  
              if (bitmask==0) {
              	break;
              }
  			gpio_config_t gpioConfig;
  			gpioConfig.pin_bit_mask = bitmask;
  			gpioConfig.mode         = GPIO_MODE_OUTPUT;
  			gpioConfig.pull_up_en   = GPIO_PULLUP_DISABLE;
  			gpioConfig.pull_down_en = GPIO_PULLDOWN_ENABLE;
  			gpioConfig.intr_type    = GPIO_INTR_DISABLE;
  			gpio_config(&gpioConfig);
  			break;
  		}
  
  	// Set the GPIO reset pin to the value passed in through arg_int.
  		case U8X8_MSG_GPIO_RESET:
  			if (u8g2_esp32_hal.reset != U8G2_ESP32_HAL_UNDEFINED) {
  				gpio_set_level(u8g2_esp32_hal.reset, arg_int);
  			}
  			break;
  	// Set the GPIO client select pin to the value passed in through arg_int.
  		case U8X8_MSG_GPIO_CS:
  			if (u8g2_esp32_hal.cs != U8G2_ESP32_HAL_UNDEFINED) {
  				gpio_set_level(u8g2_esp32_hal.cs, arg_int);
  			}
  			break;
  	// Set the Software I²C pin to the value passed in through arg_int.
  		case U8X8_MSG_GPIO_I2C_CLOCK:
  			if (u8g2_esp32_hal.scl != U8G2_ESP32_HAL_UNDEFINED) {
  				gpio_set_level(u8g2_esp32_hal.scl, arg_int);
  //				printf("%c",(arg_int==1?'C':'c'));
  			}
  			break;
  	// Set the Software I²C pin to the value passed in through arg_int.
  		case U8X8_MSG_GPIO_I2C_DATA:
  			if (u8g2_esp32_hal.sda != U8G2_ESP32_HAL_UNDEFINED) {
  				gpio_set_level(u8g2_esp32_hal.sda, arg_int);
  //				printf("%c",(arg_int==1?'D':'d'));
  			}
  			break;
  
  	// Delay for the number of milliseconds passed in through arg_int.
  		case U8X8_MSG_DELAY_MILLI:
  			vTaskDelay(arg_int/portTICK_PERIOD_MS);
  			break;
  	}
  	return 0;
  } // u8g2_esp32_gpio_and_delay_cb
  