cpu/samd21: uart: now using padd setting from board config

Notice the extra fields in uart_conf_t for rx_pad and tx_pad.

boards/samr21-xpro/include/periph_conf.h

@@ -105,8 +105,8 @@ extern "C" {
  */
 static const uart_conf_t uart_config[] = {
     /* device, RX pin, TX pin, mux */
-    {&SERCOM0->USART, GPIO_PIN(PA,5), GPIO_PIN(PA,4), GPIO_MUX_D},
-    {&SERCOM5->USART, GPIO_PIN(PA,23), GPIO_PIN(PA,22), GPIO_MUX_D},
+    {&SERCOM0->USART, GPIO_PIN(PA,5),  GPIO_PIN(PA,4),  GPIO_MUX_D, SERCOM_RX_PAD_1, UART_TX_PAD_0},
+    {&SERCOM5->USART, GPIO_PIN(PA,23), GPIO_PIN(PA,22), GPIO_MUX_D, SERCOM_RX_PAD_1, UART_TX_PAD_0},
 };
 
 /* interrupt function name mapping */

cpu/samd21/periph/uart.c

@@ -86,11 +86,12 @@ static int init_base(uart_t uart, uint32_t baudrate)
     /* reset the UART device */
     dev->CTRLA.reg = SERCOM_USART_CTRLA_SWRST;
     while (dev->SYNCBUSY.reg & SERCOM_USART_SYNCBUSY_SWRST) {}
-    /* set asynchronous mode w/o parity, LSB first, PAD0 to TX, PAD1 to RX and
+    /* set asynchronous mode w/o parity, LSB first, PADn to TX, PADn to RX and
      * use internal clock */
     dev->CTRLA.reg = (SERCOM_USART_CTRLA_DORD |
-                      SERCOM_USART_CTRLA_RXPO(0x1) |
-                      SERCOM_USART_CTRLA_SAMPR(0x1) |
+                      SERCOM_USART_CTRLA_TXPO(uart_config[uart].tx_pad) |
+                      SERCOM_USART_CTRLA_RXPO(uart_config[uart].rx_pad) |
+                      SERCOM_USART_CTRLA_SAMPR(0x1) |			// 1: x16 sample rate
                       SERCOM_USART_CTRLA_MODE_USART_INT_CLK);
     /* set baudrate */
     dev->BAUD.FRAC.FP = (baud % 10);