diff -r 8c88a3d8ecf2 -r 232f318a6b51 main/u8g2_esp32_hal.h
--- a/main/u8g2_esp32_hal.h	Sat Jun 13 23:16:50 2020 +0200
+++ b/main/u8g2_esp32_hal.h	Sun Jun 14 14:53:06 2020 +0200
@@ -12,29 +12,47 @@
 #include "driver/spi_master.h"
 #include "driver/i2c.h"
 
-#define U8G2_ESP32_HAL_UNDEFINED (-1)
+#define U8G2_ESP32_HAL_UNDEFINED	(-1)			///<  Undefined value for this HAL
 
-#define I2C_MASTER_NUM	(CONFIG_I2C_MASTER_PORT_NUM)	///<  I2C port number for master dev (original 1)
-#define I2C_MASTER_TX_BUF_DISABLE   0      ///<  I2C master do not need buffer
-#define I2C_MASTER_RX_BUF_DISABLE   0      ///<  I2C master do not need buffer
+#define I2C_MASTER_NUM	(CONFIG_I2C_MASTER_PORT_NUM)		///<  I2C port number for master dev (original 1)
+#define I2C_MASTER_TX_BUF_DISABLE	0			///<  I2C master do not need buffer
+#define I2C_MASTER_RX_BUF_DISABLE	0			///<  I2C master do not need buffer
 #define I2C_MASTER_FREQ_HZ	(CONFIG_I2C_MASTER_FREQUENCY)	///<  I2C master clock frequency (original 50000)
-#define ACK_CHECK_EN   0x1                 ///<  I2C master will check ack from slave
-#define ACK_CHECK_DIS  0x0                 ///<  I2C master will not check ack from slave
+#define ACK_CHECK_EN			0x1			///<  I2C master will check ack from slave
+#define ACK_CHECK_DIS			0x0			///<  I2C master will not check ack from slave
 
 typedef struct {
-	gpio_num_t clk;
-	gpio_num_t mosi;
-	gpio_num_t sda; // data for I²C
-	gpio_num_t scl; // clock for I²C
-	gpio_num_t cs;
-	gpio_num_t reset;
+	gpio_num_t clk;				///< SPI clock
+	gpio_num_t mosi;			///< SPI mosi
+	gpio_num_t sda;				///< data for I²C
+	gpio_num_t scl;				///< clock for I²C
+	gpio_num_t cs;				///< SPI cs
+	gpio_num_t reset;			///< SPI reset
 	gpio_num_t dc;
-} u8g2_esp32_hal_t ;
+} u8g2_esp32_hal_t;				///< HAL structure
 
 #define U8G2_ESP32_HAL_DEFAULT {U8G2_ESP32_HAL_UNDEFINED, U8G2_ESP32_HAL_UNDEFINED, U8G2_ESP32_HAL_UNDEFINED, U8G2_ESP32_HAL_UNDEFINED, U8G2_ESP32_HAL_UNDEFINED, U8G2_ESP32_HAL_UNDEFINED, U8G2_ESP32_HAL_UNDEFINED }
 
+/**
+ * @brief Initialze the ESP32 HAL.
+ */
 void u8g2_esp32_hal_init(u8g2_esp32_hal_t u8g2_esp32_hal_param);
+
+/**
+ * @brief 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);
+
+/**
+ * @brief 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);
+
+/**
+ * @brief 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);
 #endif /* U8G2_ESP32_HAL_H_ */