boards/saml21-xpro: add i2c configuration

boards/saml21-xpro/Makefile.features

@@ -3,6 +3,7 @@ FEATURES_PROVIDED += periph_adc
 FEATURES_PROVIDED += periph_cpuid
 FEATURES_PROVIDED += periph_flashpage
 FEATURES_PROVIDED += periph_gpio
+FEATURES_PROVIDED += periph_i2c
 FEATURES_PROVIDED += periph_rtc
 FEATURES_PROVIDED += periph_rtt
 FEATURES_PROVIDED += periph_spi

boards/saml21-xpro/include/periph_conf.h

@@ -96,7 +96,23 @@ static const spi_conf_t spi_config[] = {
  * @name    I2C configuration
  * @{
  */
-#define I2C_NUMOF          (0)
+#define I2C_NUMOF          (1U)
+#define I2C_0_EN            1
+#define I2C_1_EN            0
+#define I2C_2_EN            0
+#define I2C_3_EN            0
+#define I2C_IRQ_PRIO        1
+
+#define I2C_0_DEV           SERCOM2->I2CM
+#define I2C_0_IRQ           SERCOM2_IRQn
+#define I2C_0_ISR           isr_sercom2
+/* I2C 0 GCLK */
+#define I2C_0_GCLK_ID       SERCOM2_GCLK_ID_CORE
+#define I2C_0_GCLK_ID_SLOW  SERCOM2_GCLK_ID_SLOW
+/* I2C 0 pin configuration */
+#define I2C_0_SDA           GPIO_PIN(PA, 8)
+#define I2C_0_SCL           GPIO_PIN(PA, 9)
+#define I2C_0_MUX           GPIO_MUX_D
 /** @} */
 
 /**