File content as of revision 171:3a7713b1edbc:

/**
 *
 * \file
 *
 * \brief SAM SERCOM USART Driver
 *
 * Copyright (C) 2012-2015 Atmel Corporation. All rights reserved.
 *
 * \asf_license_start
 *
 * \page License
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * 3. The name of Atmel may not be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * 4. This software may only be redistributed and used in connection with an
 *    Atmel microcontroller product.
 *
 * THIS SOFTWARE IS PROVIDED BY ATMEL "AS IS" AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT ARE
 * EXPRESSLY AND SPECIFICALLY DISCLAIMED. IN NO EVENT SHALL ATMEL BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 * \asf_license_stop
 *
 */
/*
 * Support and FAQ: visit <a href="http://www.atmel.com/design-support/">Atmel Support</a>
 */
#ifndef USART_H_INCLUDED
#define USART_H_INCLUDED

/**
 * \defgroup asfdoc_sam0_sercom_usart_group SAM Serial USART Driver (SERCOM USART)
 *
 * This driver for Atmel&reg; | SMART SAM devices provides an interface for the configuration
 * and management of the SERCOM module in its USART mode to transfer or receive
 * USART data frames. The following driver API modes are covered by this
 * manual:
 *
 *  - Polled APIs
 * \if USART_CALLBACK_MODE
 *  - Callback APIs
 * \endif
 *
 * The following peripherals are used by this module:
 * - SERCOM (Serial Communication Interface)
 *
 * The following devices can use this module:
 *  - Atmel | SMART SAM D20/D21
 *  - Atmel | SMART SAM R21
 *  - Atmel | SMART SAM D10/D11
 *  - Atmel | SMART SAM L21
 *  - Atmel | SMART SAM DAx
 *  - Atmel | SMART SAM C20/C21
 *
 * The outline of this documentation is as follows:
 * - \ref asfdoc_sam0_sercom_usart_prerequisites
 * - \ref asfdoc_sam0_sercom_usart_overview
 * - \ref asfdoc_sam0_sercom_usart_special_considerations
 * - \ref asfdoc_sam0_sercom_usart_extra_info
 * - \ref asfdoc_sam0_sercom_usart_examples
 * - \ref asfdoc_sam0_sercom_usart_api_overview
 *
 * \section asfdoc_sam0_sercom_usart_prerequisites Prerequisites
 *
 * To use the USART you need to have a GCLK generator enabled and running
 * that can be used as the SERCOM clock source. This can either be configured
 * in conf_clocks.h or by using the system clock driver.
 *
 * \section asfdoc_sam0_sercom_usart_overview Module Overview
 *
 * This driver will use one (or more) SERCOM interfaces on the system
 * and configure it to run as a USART interface in either synchronous
 * or asynchronous mode.
 *
 * \subsection asfdoc_sam0_sercom_usart_features Driver Feature Macro Definition
 * <table>
 *  <tr>
 *    <th>Driver Feature Macro</th>
 *    <th>Supported devices</th>
 *  </tr>
 *  <tr>
 *    <td>FEATURE_USART_SYNC_SCHEME_V2</td>
 *    <td>SAM D21/R21/D10/D11/L21/DAx/C20/C21</td>
 *  </tr>
 *  <tr>
 *    <td>FEATURE_USART_OVER_SAMPLE</td>
 *    <td>SAM D21/R21/D10/D11/L21/DAx/C20/C21</td>
 *  </tr>
 *  <tr>
 *    <td>FEATURE_USART_HARDWARE_FLOW_CONTROL</td>
 *    <td>SAM D21/R21/D10/D11/L21/DAx/C20/C21</td>
 *  </tr>
 *  <tr>
 *    <td>FEATURE_USART_IRDA</td>
 *    <td>SAM D21/R21/D10/D11/L21/DAx/C20/C21</td>
 *  </tr>
 *  <tr>
 *    <td>FEATURE_USART_LIN_SLAVE</td>
 *    <td>SAM D21/R21/D10/D11/L21/DAx/C20/C21</td>
 *  </tr>
 *  <tr>
 *    <td>FEATURE_USART_COLLISION_DECTION</td>
 *    <td>SAM D21/R21/D10/D11/L21/DAx/C20/C21</td>
 *  </tr>
 *  <tr>
 *    <td>FEATURE_USART_START_FRAME_DECTION</td>
 *    <td>SAM D21/R21/D10/D11/L21/DAx/C20/C21</td>
 *  </tr>
 *  <tr>
 *    <td>FEATURE_USART_IMMEDIATE_BUFFER_OVERFLOW_NOTIFICATION</td>
 *    <td>SAM D21/R21/D10/D11/L21/DAx/C20/C21</td>
 *  </tr>
 *  <tr>
 *    <td>FEATURE_USART_RS485</td>
 *    <td>SAM C20/C21</td>
 *  </tr>
 * <tr>
 *    <td>FEATURE_USART_LIN_MASTER</td>
 *    <td>SAM C20/C21</td>
 *  </tr>
 * </table>
 * \note The specific features are only available in the driver when the
 * selected device supports those features.
 *
 * \subsection asfdoc_sam0_sercom_usart_overview_frame_format Frame Format
 *
 * Communication is based on frames, where the frame format can be customized
 * to accommodate a wide range of standards. A frame consists of a start bit,
 * a number of data bits, an optional parity bit for error detection as well
 * as a configurable length stop bit(s) - see
 * \ref asfdoc_sam0_sercom_usart_frame_diagram "the figure below".
 * \ref asfdoc_sam0_sercom_usart_frame_params "The table below" shows the
 * available parameters you can change in a frame.
 *
 * \anchor asfdoc_sam0_sercom_usart_frame_params
 * <table>
 *  <caption>USART Frame Parameters</caption>
 *  <tr>
 *      <th>Parameter</th>
 *      <th>Options</th>
 *  </tr>
 *  <tr>
 *      <td>Start bit</td>
 *      <td>1</td>
 *  </tr>
 *  <tr>
 *      <td>Data bits</td>
 *      <td>5, 6, 7, 8, 9</td>
 *  </tr>
 *  <tr>
 *      <td>Parity bit</td>
 *      <td>None, Even, Odd</td>
 *  </tr>
 *  <tr>
 *      <td>Stop bits</td>
 *      <td>1, 2</td>
 *  </tr>
 * </table>
 *
 * \anchor asfdoc_sam0_sercom_usart_frame_diagram
 * \image html usart_frame.svg "USART Frame Overview" width=100%
 *
 * \subsection asfdoc_sam0_sercom_usart_overview_sync Synchronous Mode
 *
 * In synchronous mode a dedicated clock line is provided; either by the USART
 * itself if in master mode, or by an external master if in slave mode.
 * Maximum transmission speed is the same as the GCLK clocking the USART
 * peripheral when in slave mode, and the GCLK divided by two if in
 * master mode. In synchronous mode the interface needs three lines to
 * communicate:
 * - TX (Transmit pin)
 * - RX (Receive pin)
 * - XCK (Clock pin)
 *
 * \subsubsection asfdoc_sam0_sercom_usart_overview_sync_sampling Data Sampling
 * In synchronous mode the data is sampled on either the rising or falling edge
 * of the clock signal. This is configured by setting the clock polarity in the
 * configuration struct.
 *
 * \subsection asfdoc_sam0_sercom_usart_overview_async Asynchronous Mode
 *
 * In asynchronous mode no dedicated clock line is used, and the communication
 * is based on matching the clock speed on the transmitter and receiver. The
 * clock is generated from the internal SERCOM baudrate generator, and the
 * frames are synchronized by using the frame start bits. Maximum transmission
 * speed is limited to the SERCOM GCLK divided by 16.
 * In asynchronous mode the interface only needs two lines to communicate:
 * - TX (Transmit pin)
 * - RX (Receive pin)
 *
 * \subsubsection asfdoc_sam0_sercom_usart_overview_async_clock_matching Transmitter/receiver Clock Matching
 *
 * For successful transmit and receive using the asynchronous mode the receiver
 * and transmitter clocks needs to be closely matched. When receiving a frame
 * that does not match the selected baudrate closely enough the receiver will
 * be unable to synchronize the frame(s), and garbage transmissions will
 * result.
 *
 * \subsection asfdoc_sam0_sercom_usart_parity Parity
 * Parity can be enabled to detect if a transmission was in error. This is done
 * by counting the number of "1" bits in the frame. When using Even parity the
 * parity bit will be set if the total number of "1"s in the frame are an even
 * number. If using Odd parity the parity bit will be set if the total number
 * of "1"s are Odd.
 *
 * When receiving a character the receiver will count the number of "1"s in the
 * frame and give an error if the received frame and parity bit disagree.
 *
 * \subsection asfdoc_sam0_sercom_usart_overview_pin_configuration GPIO Configuration
 *
 * The SERCOM module has four internal pads; the RX pin can be placed freely on
 * any one of the four pads, and the TX and XCK pins have two predefined
 * positions that can be selected as a pair. The pads can then be routed to an
 * external GPIO pin using the normal pin multiplexing scheme on the SAM.
 *
 * \section asfdoc_sam0_sercom_usart_special_considerations Special Considerations
 *
 * \if USART_CALLBACK_MODE
 * Never execute large portions of code in the callbacks. These
 * are run from the interrupt routine, and thus having long callbacks will
 * keep the processor in the interrupt handler for an equally long time.
 * A common way to handle this is to use global flags signaling the
 * main application that an interrupt event has happened, and only do the
 * minimal needed processing in the callback.
 * \else
 * No special considerations.
 * \endif
 *
 * \section asfdoc_sam0_sercom_usart_extra_info Extra Information
 *
 * For extra information, see \ref asfdoc_sam0_sercom_usart_extra. This includes:
 * - \ref asfdoc_sam0_sercom_usart_extra_acronyms
 * - \ref asfdoc_sam0_sercom_usart_extra_dependencies
 * - \ref asfdoc_sam0_sercom_usart_extra_errata
 * - \ref asfdoc_sam0_sercom_usart_extra_history
 *
 * \section asfdoc_sam0_sercom_usart_examples Examples
 *
 * For a list of examples related to this driver, see
 * \ref asfdoc_sam0_sercom_usart_exqsg.
 *
 * \section asfdoc_sam0_sercom_usart_api_overview API Overview
 * @{
 */

#include <compiler.h>
#include <sercom.h>
#include <pinmux.h>

#if USART_CALLBACK_MODE == true
#  include <sercom_interrupt.h>
#endif

#ifdef __cplusplus
extern "C" {
#endif

/**
 * \name Driver Feature Definition
 * Define SERCOM USART features set according to different device family.
 * @{
 */
#if (SAMD21) || (SAMR21) || (SAMD10) || (SAMD11) || (SAML21) || \
	(SAMDA1) || (SAMC20) || (SAMC21) || defined(__DOXYGEN__)
/** Usart sync scheme version 2. */
#  define FEATURE_USART_SYNC_SCHEME_V2
/** Usart over sampling. */
#  define FEATURE_USART_OVER_SAMPLE
/** Usart hardware control flow. */
#  define FEATURE_USART_HARDWARE_FLOW_CONTROL
/** IrDA mode. */
#  define FEATURE_USART_IRDA
/** LIN slave mode. */
#  define FEATURE_USART_LIN_SLAVE
/** Usart collision detection. */
#  define FEATURE_USART_COLLISION_DECTION
/** Usart start frame detection. */
#  define FEATURE_USART_START_FRAME_DECTION
/** Usart start buffer overflow notification. */
#  define FEATURE_USART_IMMEDIATE_BUFFER_OVERFLOW_NOTIFICATION
#endif

#if (SAMC20) || (SAMC21) || defined(__DOXYGEN__)
/** LIN master mode. */
#define FEATURE_USART_LIN_MASTER
/** RS485 mode. */
#  define FEATURE_USART_RS485
#endif
/*@}*/

#ifdef FEATURE_USART_LIN_MASTER
/**
 * \brief LIN Node Type.
 *
 * LIN node type.
 */
enum lin_node_type {
    /** LIN master mode */
    LIN_MASTER_NODE = SERCOM_USART_CTRLA_FORM(0x02),
    /** LIN slave mode */
    LIN_SLAVE_NODE = SERCOM_USART_CTRLA_FORM(0x04),
    /** Neither LIN master nor LIN slave mode */
    LIN_INVALID_MODE = SERCOM_USART_CTRLA_FORM(0x00),
};

/**
 * \brief LIN Master Command Enum.
 *
 * LIN master command enum.
 */
enum lin_master_cmd {
    /** LIN master software control transmission command */
    LIN_MASTER_SOFTWARE_CONTROL_TRANSMIT_CMD = SERCOM_USART_CTRLB_LINCMD(0x01),
    /** LIN master automatically transmission command */
    LIN_MASTER_AUTO_TRANSMIT_CMD = SERCOM_USART_CTRLB_LINCMD(0x02),
};

/**
 * \brief LIN Master Header Delay.
 *
 * LIN master header delay between break and sync transmission,
 * and between the sync and identifier (ID) fields.
 * This field is only valid when using automatically transmission command
 */
enum lin_master_header_delay {
    /** Delay between break and sync transmission is 1 bit time.
    	Delay between sync and ID transmission is 1 bit time. */
    LIN_MASTER_HEADER_DELAY_0 = SERCOM_USART_CTRLC_HDRDLY(0x0),
    /** Delay between break and sync transmission is 4 bit time.
    	Delay between sync and ID transmission is 4 bit time. */
    LIN_MASTER_HEADER_DELAY_1 = SERCOM_USART_CTRLC_HDRDLY(0x01),
    /** Delay between break and sync transmission is 8 bit time.
    	Delay between sync and ID transmission is 4 bit time. */
    LIN_MASTER_HEADER_DELAY_2 = SERCOM_USART_CTRLC_HDRDLY(0x02),
    /** Delay between break and sync transmission is 14 bit time.
    	Delay between sync and ID transmission is 4 bit time. */
    LIN_MASTER_HEADER_DELAY_3 = SERCOM_USART_CTRLC_HDRDLY(0x03),
};

/**
 * \brief LIN Master Break Length.
 *
 * Length of the break field transmitted when in LIN master mode
 */
enum lin_master_break_length {
    /** Break field transmission is 13 bit times. */
    LIN_MASTER_BREAK_LENGTH_13_BIT = SERCOM_USART_CTRLC_BRKLEN(0x0),
    /** Break field transmission is 17 bit times. */
    LIN_MASTER_BREAK_LENGTH_17_BIT = SERCOM_USART_CTRLC_BRKLEN(0x1),
    /** Break field transmission is 21 bit times. */
    LIN_MASTER_BREAK_LENGTH_21_BIT = SERCOM_USART_CTRLC_BRKLEN(0x2),
    /** Break field transmission is 26 bit times. */
    LIN_MASTER_BREAK_LENGTH_26_BIT = SERCOM_USART_CTRLC_BRKLEN(0x3),
};
#endif

#ifndef PINMUX_DEFAULT
/** Default pinmux. */
#  define PINMUX_DEFAULT 0
#endif

#ifndef PINMUX_UNUSED
/** Unused pinmux. */
#  define PINMUX_UNUSED 0xFFFFFFFF
#endif

#ifndef USART_TIMEOUT
/** USART timeout value. */
#  define USART_TIMEOUT 0xFFFF
#endif

#if USART_CALLBACK_MODE == true
/**
 * \brief USART Callback enum
 *
 * Callbacks for the Asynchronous USART driver.
 */
enum usart_callback {
    /** Callback for buffer transmitted. */
    USART_CALLBACK_BUFFER_TRANSMITTED,
    /** Callback for buffer received. */
    USART_CALLBACK_BUFFER_RECEIVED,
    /** Callback for error. */
    USART_CALLBACK_ERROR,
#ifdef FEATURE_USART_LIN_SLAVE
    /** Callback for break character is received. */
    USART_CALLBACK_BREAK_RECEIVED,
#endif
#ifdef FEATURE_USART_HARDWARE_FLOW_CONTROL
    /** Callback for a change is detected on the CTS pin. */
    USART_CALLBACK_CTS_INPUT_CHANGE,
#endif
#ifdef FEATURE_USART_START_FRAME_DECTION
    /** Callback for a start condition is detected on the RxD line. */
    USART_CALLBACK_START_RECEIVED,
#endif
#  if !defined(__DOXYGEN__)
    /** Number of available callbacks. */
    USART_CALLBACK_N,
#  endif
};
#endif

/**
 * \brief USART Data Order enum
 *
 * The data order decides which of MSB or LSB is shifted out first when data is
 * transferred.
 */
enum usart_dataorder {
    /** The MSB will be shifted out first during transmission,
     *  and shifted in first during reception. */
    USART_DATAORDER_MSB = 0,
    /** The LSB will be shifted out first during transmission,
     *  and shifted in first during reception. */
    USART_DATAORDER_LSB = SERCOM_USART_CTRLA_DORD,
};

/**
 * \brief USART Transfer mode enum
 *
 * Select USART transfer mode.
 */
enum usart_transfer_mode {
    /** Transfer of data is done synchronously. */
    USART_TRANSFER_SYNCHRONOUSLY = (SERCOM_USART_CTRLA_CMODE),
    /** Transfer of data is done asynchronously. */
    USART_TRANSFER_ASYNCHRONOUSLY = 0
};

/**
 * \brief USART Parity enum
 *
 * Select parity USART parity mode.
 */
enum usart_parity {
    /** For odd parity checking, the parity bit will be set if number of
     *  ones being transferred is even. */
    USART_PARITY_ODD  = SERCOM_USART_CTRLB_PMODE,

    /** For even parity checking, the parity bit will be set if number of
     *  ones being received is odd. */
    USART_PARITY_EVEN = 0,

    /** No parity checking will be executed, and there will be no parity bit
     *  in the received frame. */
    USART_PARITY_NONE = 0xFF,
};

/**
 * \brief USART signal MUX settings
 *
 * Set the functionality of the SERCOM pins.
 *
 * See \ref asfdoc_sam0_sercom_usart_mux_settings for a description of the
 * various MUX setting options.
 */
enum usart_signal_mux_settings {
#ifdef FEATURE_USART_HARDWARE_FLOW_CONTROL
    /** MUX setting RX_0_TX_0_XCK_1. */
    USART_RX_0_TX_0_XCK_1 = (SERCOM_USART_CTRLA_RXPO(0) | SERCOM_USART_CTRLA_TXPO(0)),
    /** MUX setting RX_0_TX_2_XCK_3. */
    USART_RX_0_TX_2_XCK_3 = (SERCOM_USART_CTRLA_RXPO(0) | SERCOM_USART_CTRLA_TXPO(1)),
    /** MUX setting USART_RX_0_TX_0_RTS_2_CTS_3. */
    USART_RX_0_TX_0_RTS_2_CTS_3 = (SERCOM_USART_CTRLA_RXPO(0) | SERCOM_USART_CTRLA_TXPO(2)),
    /** MUX setting RX_1_TX_0_XCK_1. */
    USART_RX_1_TX_0_XCK_1 = (SERCOM_USART_CTRLA_RXPO(1) | SERCOM_USART_CTRLA_TXPO(0)),
    /** MUX setting RX_1_TX_2_XCK_3. */
    USART_RX_1_TX_2_XCK_3 = (SERCOM_USART_CTRLA_RXPO(1) | SERCOM_USART_CTRLA_TXPO(1)),
    /** MUX setting USART_RX_1_TX_0_RTS_2_CTS_3. */
    USART_RX_1_TX_0_RTS_2_CTS_3 = (SERCOM_USART_CTRLA_RXPO(1) | SERCOM_USART_CTRLA_TXPO(2)),
    /** MUX setting RX_2_TX_0_XCK_1. */
    USART_RX_2_TX_0_XCK_1 = (SERCOM_USART_CTRLA_RXPO(2) | SERCOM_USART_CTRLA_TXPO(0)),
    /** MUX setting RX_2_TX_2_XCK_3. */
    USART_RX_2_TX_2_XCK_3 = (SERCOM_USART_CTRLA_RXPO(2) | SERCOM_USART_CTRLA_TXPO(1)),
    /** MUX setting USART_RX_2_TX_0_RTS_2_CTS_3. */
    USART_RX_2_TX_0_RTS_2_CTS_3 = (SERCOM_USART_CTRLA_RXPO(2) | SERCOM_USART_CTRLA_TXPO(2)),
    /** MUX setting RX_3_TX_0_XCK_1. */
    USART_RX_3_TX_0_XCK_1 = (SERCOM_USART_CTRLA_RXPO(3) | SERCOM_USART_CTRLA_TXPO(0)),
    /** MUX setting RX_3_TX_2_XCK_3. */
    USART_RX_3_TX_2_XCK_3 = (SERCOM_USART_CTRLA_RXPO(3) | SERCOM_USART_CTRLA_TXPO(1)),
    /** MUX setting USART_RX_3_TX_0_RTS_2_CTS_3. */
    USART_RX_3_TX_0_RTS_2_CTS_3 = (SERCOM_USART_CTRLA_RXPO(3) | SERCOM_USART_CTRLA_TXPO(2)),
#ifdef FEATURE_USART_RS485
    /** MUX setting USART_RX_0_TX_0_XCK_1_TE_2. */
    USART_RX_0_TX_0_XCK_1_TE_2 = (SERCOM_USART_CTRLA_RXPO(0) | SERCOM_USART_CTRLA_TXPO(3)),
    /** MUX setting USART_RX_1_TX_0_XCK_1_TE_2. */
    USART_RX_1_TX_0_XCK_1_TE_2 = (SERCOM_USART_CTRLA_RXPO(1) | SERCOM_USART_CTRLA_TXPO(3)),
    /** MUX setting USART_RX_2_TX_0_XCK_1_TE_2. */
    USART_RX_2_TX_0_XCK_1_TE_2 = (SERCOM_USART_CTRLA_RXPO(2) | SERCOM_USART_CTRLA_TXPO(3)),
    /** MUX setting USART_RX_3_TX_0_XCK_1_TE_2. */
    USART_RX_3_TX_0_XCK_1_TE_2 = (SERCOM_USART_CTRLA_RXPO(3) | SERCOM_USART_CTRLA_TXPO(3)),
#endif
#else
    /** MUX setting RX_0_TX_0_XCK_1. */
    USART_RX_0_TX_0_XCK_1 = (SERCOM_USART_CTRLA_RXPO(0)),
    /** MUX setting RX_0_TX_2_XCK_3. */
    USART_RX_0_TX_2_XCK_3 = (SERCOM_USART_CTRLA_RXPO(0) | SERCOM_USART_CTRLA_TXPO),
    /** MUX setting RX_1_TX_0_XCK_1. */
    USART_RX_1_TX_0_XCK_1 = (SERCOM_USART_CTRLA_RXPO(1)),
    /** MUX setting RX_1_TX_2_XCK_3. */
    USART_RX_1_TX_2_XCK_3 = (SERCOM_USART_CTRLA_RXPO(1) | SERCOM_USART_CTRLA_TXPO),
    /** MUX setting RX_2_TX_0_XCK_1. */
    USART_RX_2_TX_0_XCK_1 = (SERCOM_USART_CTRLA_RXPO(2)),
    /** MUX setting RX_2_TX_2_XCK_3. */
    USART_RX_2_TX_2_XCK_3 = (SERCOM_USART_CTRLA_RXPO(2) | SERCOM_USART_CTRLA_TXPO),
    /** MUX setting RX_3_TX_0_XCK_1. */
    USART_RX_3_TX_0_XCK_1 = (SERCOM_USART_CTRLA_RXPO(3)),
    /** MUX setting RX_3_TX_2_XCK_3. */
    USART_RX_3_TX_2_XCK_3 = (SERCOM_USART_CTRLA_RXPO(3) | SERCOM_USART_CTRLA_TXPO),
#endif
};

/**
 * \brief USART Stop Bits enum
 *
 * Number of stop bits for a frame.
 */
enum usart_stopbits {
    /** Each transferred frame contains one stop bit. */
    USART_STOPBITS_1 = 0,
    /** Each transferred frame contains two stop bits. */
    USART_STOPBITS_2 = SERCOM_USART_CTRLB_SBMODE,
};

/**
 * \brief USART Character Size
 *
 * Number of bits for the character sent in a frame.
 */
enum usart_character_size {
    /** The char being sent in a frame is five bits long. */
    USART_CHARACTER_SIZE_5BIT = SERCOM_USART_CTRLB_CHSIZE(5),
    /** The char being sent in a frame is six bits long. */
    USART_CHARACTER_SIZE_6BIT = SERCOM_USART_CTRLB_CHSIZE(6),
    /** The char being sent in a frame is seven bits long. */
    USART_CHARACTER_SIZE_7BIT = SERCOM_USART_CTRLB_CHSIZE(7),
    /** The char being sent in a frame is eight bits long. */
    USART_CHARACTER_SIZE_8BIT = SERCOM_USART_CTRLB_CHSIZE(0),
    /** The char being sent in a frame is nine bits long. */
    USART_CHARACTER_SIZE_9BIT = SERCOM_USART_CTRLB_CHSIZE(1),
};

#ifdef FEATURE_USART_OVER_SAMPLE
/**
 * \brief USART Sample Rate
 *
 * The value of sample rate and baudrate generation mode.
 */
enum usart_sample_rate {
    /** 16x over-sampling using arithmetic baudrate generation. */
    USART_SAMPLE_RATE_16X_ARITHMETIC = SERCOM_USART_CTRLA_SAMPR(0),
    /** 16x over-sampling using fractional baudrate generation. */
    USART_SAMPLE_RATE_16X_FRACTIONAL = SERCOM_USART_CTRLA_SAMPR(1),
    /** 8x over-sampling using arithmetic baudrate generation. */
    USART_SAMPLE_RATE_8X_ARITHMETIC = SERCOM_USART_CTRLA_SAMPR(2),
    /** 8x over-sampling using fractional baudrate generation. */
    USART_SAMPLE_RATE_8X_FRACTIONAL = SERCOM_USART_CTRLA_SAMPR(3),
    /** 3x over-sampling using arithmetic baudrate generation. */
    USART_SAMPLE_RATE_3X_ARITHMETIC = SERCOM_USART_CTRLA_SAMPR(4),
};

/**
 * \brief USART Sample Adjustment
 *
 * The value of sample number used for majority voting.
 */
enum usart_sample_adjustment {
    /** The first, middle and last sample number used for majority voting is 7-8-9. */
    USART_SAMPLE_ADJUSTMENT_7_8_9 = SERCOM_USART_CTRLA_SAMPA(0),
    /** The first, middle and last sample number used for majority voting is 9-10-11. */
    USART_SAMPLE_ADJUSTMENT_9_10_11 = SERCOM_USART_CTRLA_SAMPA(1),
    /** The first, middle and last sample number used for majority voting is 11-12-13. */
    USART_SAMPLE_ADJUSTMENT_11_12_13 = SERCOM_USART_CTRLA_SAMPA(2),
    /** The first, middle and last sample number used for majority voting is 13-14-15. */
    USART_SAMPLE_ADJUSTMENT_13_14_15 = SERCOM_USART_CTRLA_SAMPA(3),
};
#endif

#ifdef FEATURE_USART_RS485
/**
 * \brief RS485 Guard Time
 *
 * The value of RS485 guard time.
 */
enum rs485_guard_time {
    /** The guard time is 0-bit time. */
    RS485_GUARD_TIME_0_BIT = 0,
    /** The guard time is 1-bit time. */
    RS485_GUARD_TIME_1_BIT,
    /** The guard time is 2-bit times. */
    RS485_GUARD_TIME_2_BIT,
    /** The guard time is 3-bit times. */
    RS485_GUARD_TIME_3_BIT,
    /** The guard time is 4-bit times. */
    RS485_GUARD_TIME_4_BIT,
    /** The guard time is 5-bit times. */
    RS485_GUARD_TIME_5_BIT,
    /** The guard time is 6-bit times. */
    RS485_GUARD_TIME_6_BIT,
    /** The guard time is 7-bit times. */
    RS485_GUARD_TIME_7_BIT,
};
#endif

/**
 * \brief USART Transceiver
 *
 * Select Receiver or Transmitter.
 */
enum usart_transceiver_type {
    /** The parameter is for the Receiver. */
    USART_TRANSCEIVER_RX,
    /** The parameter is for the Transmitter. */
    USART_TRANSCEIVER_TX,
};

/**
 * \brief USART configuration struct
 *
 * Configuration options for USART.
 */
struct usart_config {
    /** USART bit order (MSB or LSB first). */
    enum usart_dataorder data_order;
    /** USART in asynchronous or synchronous mode. */
    enum usart_transfer_mode transfer_mode;
    /** USART parity. */
    enum usart_parity parity;
    /** Number of stop bits. */
    enum usart_stopbits stopbits;
    /** USART character size. */
    enum usart_character_size character_size;
    /** USART pin out. */
    enum usart_signal_mux_settings mux_setting;
#ifdef FEATURE_USART_OVER_SAMPLE
    /** USART sample rate. */
    enum usart_sample_rate sample_rate;
    /** USART sample adjustment. */
    enum usart_sample_adjustment sample_adjustment;
#endif
#ifdef FEATURE_USART_IMMEDIATE_BUFFER_OVERFLOW_NOTIFICATION
    /** Controls when the buffer overflow status bit is asserted when a buffer overflow occurs.*/
    bool immediate_buffer_overflow_notification;
#endif
#ifdef FEATURE_USART_IRDA
    /** Enable IrDA encoding format. */
    bool encoding_format_enable;
    /** The minimum pulse length that is required for a pulse to be accepted by the IrDA receiver. */
    uint8_t receive_pulse_length;
#endif
#ifdef FEATURE_USART_LIN_SLAVE
    /** Enable LIN Slave Support. */
    bool lin_slave_enable;
#endif

#ifdef FEATURE_USART_LIN_MASTER
    /** LIN node type. */
    enum lin_node_type lin_node;
    /** LIN master header delay. */
    enum lin_master_header_delay lin_header_delay;
    /** LIN Master Break Length. */
    enum lin_master_break_length lin_break_length;
#endif

#ifdef FEATURE_USART_START_FRAME_DECTION
    /** Enable start of frame dection. */
    bool start_frame_detection_enable;
#endif
#ifdef FEATURE_USART_RS485
    /** RS485 guard time. */
    enum rs485_guard_time rs485_guard_time;
#endif
#ifdef FEATURE_USART_COLLISION_DECTION
    /** Enable collision dection. */
    bool collision_detection_enable;
#endif
    /** USART baudrate. */
    uint32_t baudrate;
    /** Enable receiver. */
    bool receiver_enable;
    /** Enable transmitter. */
    bool transmitter_enable;

    /** USART Clock Polarity.
     * If true, data changes on falling XCK edge and
     * is sampled at rising edge.
     * If false, data changes on rising XCK edge and
     * is sampled at falling edge.
     * */
    bool clock_polarity_inverted;

    /** States whether to use the external clock applied to the XCK pin.
     * In synchronous mode the shift register will act directly on the XCK clock.
     * In asynchronous mode the XCK will be the input to the USART hardware module.
     */
    bool use_external_clock;
    /** External clock frequency in synchronous mode.
     * This must be set if \c use_external_clock is true. */
    uint32_t ext_clock_freq;
    /** If true the USART will be kept running in Standby sleep mode. */
    bool run_in_standby;
    /** GCLK generator source. */
    enum gclk_generator generator_source;
    /** PAD0 pinmux.
     *
     * If current USARTx has several alternative multiplexing I/O pin for PAD0, then
     * only one peripheral multiplexing I/O can be enabled for current USARTx PAD0
     * function. Make sure other alternative multiplexing I/O associated current
     * USARTx PAD0 is not setup usart function.
     */
    uint32_t pinmux_pad0;
    /** PAD1 pinmux.
     *
     * If current USARTx has several alternative multiplexing I/O pin for PAD1, then
     * only one peripheral multiplexing I/O can be enabled for current USARTx PAD1
     * function. Make sure other alternative multiplexing I/O associated current
     * USARTx PAD1 is not setup usart function.
     */
    uint32_t pinmux_pad1;
    /** PAD2 pinmux.
     *
     * If current USARTx has several alternative multiplexing I/O pin for PAD2, then
     * only one peripheral multiplexing I/O can be enabled for current USARTx PAD2
     * function. Make sure other alternative multiplexing I/O associated current
     * USARTx PAD2 is not setup usart function.
     */
    uint32_t pinmux_pad2;
    /** PAD3 pinmux.
     *
     * If current USARTx has several alternative multiplexing I/O pin for PAD3, then
     * only one peripheral multiplexing I/O can be enabled for current USARTx PAD3
     * function. Make sure other alternative multiplexing I/O associated current
     * USARTx PAD3 is not setup usart function.
     */
    uint32_t pinmux_pad3;
};

#if USART_CALLBACK_MODE == true
/**
 * \brief USART module instance
 *
 * Forward Declaration for the device instance.
 */
struct usart_module;

/**
 * \brief USART callback type
 *
 * Type of the callback functions.
 */
typedef void (*usart_callback_t)(struct usart_module *const module);
#endif

/**
 * \brief SERCOM USART driver software device instance structure.
 *
 * SERCOM USART driver software instance structure, used to retain software
 * state information of an associated hardware module instance.
 *
 * \note The fields of this structure should not be altered by the user
 *       application; they are reserved for module-internal use only.
 */
struct usart_module {
#if !defined(__DOXYGEN__)
    /** Pointer to the hardware instance. */
    Sercom *hw;
    /** Module lock. */
    volatile bool locked;
    /** Character size of the data being transferred. */
    enum usart_character_size character_size;
    /** Receiver enabled. */
    bool receiver_enabled;
    /** Transmitter enabled. */
    bool transmitter_enabled;
#ifdef FEATURE_USART_LIN_SLAVE
    /** LIN Slave Support enabled. */
    bool lin_slave_enabled;
#endif
#ifdef FEATURE_USART_START_FRAME_DECTION
    /** Start of frame dection enabled. */
    bool start_frame_detection_enabled;
#endif
#  if USART_CALLBACK_MODE == true
    /** Array to store callback function pointers in. */
    usart_callback_t callback[USART_CALLBACK_N];
    /** Buffer pointer to where the next received character will be put. */
    volatile uint8_t *rx_buffer_ptr;

    /** Buffer pointer to where the next character will be transmitted from.
    **/
    volatile uint8_t *tx_buffer_ptr;
    /** Remaining characters to receive. */
    volatile uint16_t remaining_rx_buffer_length;
    /** Remaining characters to transmit. */
    volatile uint16_t remaining_tx_buffer_length;
    /** Bit mask for callbacks registered. */
    uint8_t callback_reg_mask;
    /** Bit mask for callbacks enabled. */
    uint8_t callback_enable_mask;
    /** Holds the status of the ongoing or last read operation. */
    volatile enum status_code rx_status;
    /** Holds the status of the ongoing or last write operation. */
    volatile enum status_code tx_status;
#  endif
#endif
};

/**
* \name Lock/Unlock
* @{
*/

/**
 * \brief Attempt to get lock on driver instance
 *
 * This function checks the instance's lock, which indicates whether or not it
 * is currently in use, and sets the lock if it was not already set.
 *
 * The purpose of this is to enable exclusive access to driver instances, so
 * that, e.g., transactions by different services will not interfere with each
 * other.
 *
 * \param[in,out] module Pointer to the driver instance to lock
 *
 * \retval STATUS_OK If the module was locked
 * \retval STATUS_BUSY If the module was already locked
 */
static inline enum status_code usart_lock(
    struct usart_module *const module)
{
    enum status_code status;

    system_interrupt_enter_critical_section();

    if (module->locked) {
        status = STATUS_BUSY;
    } else {
        module->locked = true;
        status = STATUS_OK;
    }

    system_interrupt_leave_critical_section();

    return status;
}

/**
 * \brief Unlock driver instance
 *
 * This function clears the instance lock, indicating that it is available for
 * use.
 *
 * \param[in,out] module Pointer to the driver instance to lock
 *
 */
static inline void usart_unlock(struct usart_module *const module)
{
    module->locked = false;
}

/** @} */

/**
 * \brief Check if peripheral is busy syncing registers across clock domains
 *
 * Return peripheral synchronization status. If doing a non-blocking
 * implementation this function can be used to check the sync state and hold of
 * any new actions until sync is complete. If this functions is not run; the
 * functions will block until the sync has completed.
 *
 * \param[in]  module  Pointer to peripheral module
 *
 * \return Peripheral sync status.
 *
 * \retval true   Peripheral is busy syncing
 * \retval false  Peripheral is not busy syncing and can be read/written without
 *                stalling the bus.
 */
static inline bool usart_is_syncing(
    const struct usart_module *const module)
{
    /* Sanity check arguments */
    Assert(module);
    Assert(module->hw);

    SercomUsart *const usart_hw = &(module->hw->USART);

#ifdef FEATURE_USART_SYNC_SCHEME_V2
    return (usart_hw->SYNCBUSY.reg);
#else
    return (usart_hw->STATUS.reg & SERCOM_USART_STATUS_SYNCBUSY);
#endif
}

#if !defined (__DOXYGEN__)
/**
 * \internal
 * Waits until synchronization is complete
 */
static inline void _usart_wait_for_sync(
    const struct usart_module *const module)
{
    /* Sanity check. */
    Assert(module);

    while (usart_is_syncing(module)) {
        /* Wait until the synchronization is complete */
    }
}
#endif

/**
 * \brief Initializes the device to predefined defaults
 *
 * Initialize the USART device to predefined defaults:
 * - 8-bit asynchronous USART
 * - No parity
 * - One stop bit
 * - 9600 baud
 * - Transmitter enabled
 * - Receiver enabled
 * - GCLK generator 0 as clock source
 * - Default pin configuration
 *
 * The configuration struct will be updated with the default
 * configuration.
 *
 * \param[in,out] config  Pointer to configuration struct
 */
static inline void usart_get_config_defaults(
    struct usart_config *const config)
{
    /* Sanity check arguments */
    Assert(config);

    /* Set default config in the config struct */
    config->data_order       = USART_DATAORDER_LSB;
    config->transfer_mode    = USART_TRANSFER_ASYNCHRONOUSLY;
    config->parity           = USART_PARITY_NONE;
    config->stopbits         = USART_STOPBITS_1;
    config->character_size   = USART_CHARACTER_SIZE_8BIT;
    config->baudrate         = 9600;
    config->receiver_enable  = true;
    config->transmitter_enable = true;
    config->clock_polarity_inverted = false;
    config->use_external_clock = false;
    config->ext_clock_freq   = 0;
    config->mux_setting      = USART_RX_1_TX_2_XCK_3;
    config->run_in_standby   = false;
    config->generator_source = GCLK_GENERATOR_0;
    config->pinmux_pad0      = PINMUX_DEFAULT;
    config->pinmux_pad1      = PINMUX_DEFAULT;
    config->pinmux_pad2      = PINMUX_DEFAULT;
    config->pinmux_pad3      = PINMUX_DEFAULT;
#ifdef FEATURE_USART_OVER_SAMPLE
    config->sample_adjustment     = USART_SAMPLE_ADJUSTMENT_7_8_9;
    config->sample_rate           = USART_SAMPLE_RATE_16X_ARITHMETIC;
#endif
#ifdef FEATURE_USART_LIN_SLAVE
    config->lin_slave_enable      = false;
#endif

#ifdef FEATURE_USART_LIN_MASTER
    config->lin_node = LIN_INVALID_MODE;
    config->lin_header_delay = LIN_MASTER_HEADER_DELAY_0;
    config->lin_break_length = LIN_MASTER_BREAK_LENGTH_13_BIT;
#endif

#ifdef FEATURE_USART_IMMEDIATE_BUFFER_OVERFLOW_NOTIFICATION
    config->immediate_buffer_overflow_notification      = false;
#endif
#ifdef FEATURE_USART_START_FRAME_DECTION
    config->start_frame_detection_enable                = false;
#endif
#ifdef FEATURE_USART_IRDA
    config->encoding_format_enable                      = false;
    config->receive_pulse_length                        = 19;
#endif
#ifdef FEATURE_USART_COLLISION_DECTION
    config->collision_detection_enable                  = false;
#endif
#ifdef FEATURE_USART_RS485
    config->rs485_guard_time = RS485_GUARD_TIME_0_BIT;
#endif
}

enum status_code usart_init(
    struct usart_module *const module,
    Sercom *const hw,
    const struct usart_config *const config);

/**
 * \brief Enable the module
 *
 * Enables the USART module.
 *
 * \param[in]  module  Pointer to USART software instance struct
 */
static inline void usart_enable(
    const struct usart_module *const module)
{
    /* Sanity check arguments */
    Assert(module);
    Assert(module->hw);

    /* Get a pointer to the hardware module instance */
    SercomUsart *const usart_hw = &(module->hw->USART);

#if USART_CALLBACK_MODE == true
    /* Enable Global interrupt for module */
    system_interrupt_enable(_sercom_get_interrupt_vector(module->hw));
#endif

    /* Wait until synchronization is complete */
    _usart_wait_for_sync(module);

    /* Enable USART module */
    usart_hw->CTRLA.reg |= SERCOM_USART_CTRLA_ENABLE;
}

/**
 * \brief Disable module
 *
 * Disables the USART module.
 *
 * \param[in]  module  Pointer to USART software instance struct
 */
static inline void usart_disable(
    const struct usart_module *const module)
{
    /* Sanity check arguments */
    Assert(module);
    Assert(module->hw);

    /* Get a pointer to the hardware module instance */
    SercomUsart *const usart_hw = &(module->hw->USART);

#if USART_CALLBACK_MODE == true
    /* Disable Global interrupt for module */
    system_interrupt_disable(_sercom_get_interrupt_vector(module->hw));
#endif
    /* Wait until synchronization is complete */
    _usart_wait_for_sync(module);

    /* Disable USART module */
    usart_hw->CTRLA.reg &= ~SERCOM_USART_CTRLA_ENABLE;
}

/**
 * \brief Resets the USART module
 *
 * Disables and resets the USART module.
 *
 * \param[in]  module  Pointer to the USART software instance struct
 */
static inline void usart_reset(
    const struct usart_module *const module)
{
    /* Sanity check arguments */
    Assert(module);
    Assert(module->hw);

    /* Get a pointer to the hardware module instance */
    SercomUsart *const usart_hw = &(module->hw->USART);

    usart_disable(module);

    /* Wait until synchronization is complete */
    _usart_wait_for_sync(module);

    /* Reset module */
    usart_hw->CTRLA.reg = SERCOM_USART_CTRLA_SWRST;
}

/**
 * \name Writing and Reading
 * @{
 */
enum status_code usart_write_wait(
    struct usart_module *const module,
    const uint16_t tx_data);

enum status_code usart_read_wait(
    struct usart_module *const module,
    uint16_t *const rx_data);

enum status_code usart_write_buffer_wait(
    struct usart_module *const module,
    const uint8_t *tx_data,
    uint16_t length);

enum status_code usart_read_buffer_wait(
    struct usart_module *const module,
    uint8_t *rx_data,
    uint16_t length);
/** @} */

/**
 * \name Enabling/Disabling Receiver and Transmitter
 * @{
 */

/**
 * \brief Enable Transceiver
 *
 * Enable the given transceiver. Either RX or TX.
 *
 * \param[in]  module            Pointer to USART software instance struct
 * \param[in]  transceiver_type  Transceiver type
 */
static inline void usart_enable_transceiver(
    struct usart_module *const module,
    enum usart_transceiver_type transceiver_type)
{
    /* Sanity check arguments */
    Assert(module);
    Assert(module->hw);

    /* Get a pointer to the hardware module instance */
    SercomUsart *const usart_hw = &(module->hw->USART);

    /* Wait until synchronization is complete */
    _usart_wait_for_sync(module);

    switch (transceiver_type) {
        case USART_TRANSCEIVER_RX:
            /* Enable RX */
            usart_hw->CTRLB.reg |= SERCOM_USART_CTRLB_RXEN;
            module->receiver_enabled = true;
            break;

        case USART_TRANSCEIVER_TX:
            /* Enable TX */
            usart_hw->CTRLB.reg |= SERCOM_USART_CTRLB_TXEN;
            module->transmitter_enabled = true;
            break;
    }
    _usart_wait_for_sync(module);
}

/**
 * \brief Disable Transceiver
 *
 * Disable the given transceiver (RX or TX).
 *
 * \param[in]  module            Pointer to USART software instance struct
 * \param[in]  transceiver_type  Transceiver type
 */
static inline void usart_disable_transceiver(
    struct usart_module *const module,
    enum usart_transceiver_type transceiver_type)
{
    /* Sanity check arguments */
    Assert(module);
    Assert(module->hw);

    /* Get a pointer to the hardware module instance */
    SercomUsart *const usart_hw = &(module->hw->USART);

    /* Wait until synchronization is complete */
    _usart_wait_for_sync(module);

    switch (transceiver_type) {
        case USART_TRANSCEIVER_RX:
            /* Disable RX */
            usart_hw->CTRLB.reg &= ~SERCOM_USART_CTRLB_RXEN;
            module->receiver_enabled = false;
            break;

        case USART_TRANSCEIVER_TX:
            /* Disable TX */
            usart_hw->CTRLB.reg &= ~SERCOM_USART_CTRLB_TXEN;
            module->transmitter_enabled = false;
            break;
    }
}

/** @} */

#ifdef FEATURE_USART_LIN_MASTER
/**
 * \name LIN Master Command and Status
 * @{
 */

/**
 * \brief Sending LIN command.
 *
 * Sending LIN command.
 *
 * \param[in]  module Pointer to USART software instance struct.
 * \param[in]  cmd  Cammand type.
 */
static inline void lin_master_send_cmd(
    struct usart_module *const module,
    enum lin_master_cmd cmd)
{
    SercomUsart *const usart_hw = &(module->hw->USART);
    _usart_wait_for_sync(module);
    usart_hw->CTRLB.reg |= cmd;
}

/**
 * \brief Get LIN transmission status.
 *
 * Get LIN transmission status.
 *
 * \param[in]  module Pointer to USART software instance struct.
 *
 * \return Status of LIN master transmission.
 * \retval true   Data transmission completed
 * \retval false  Transmission is ongoing
 */
static inline bool lin_master_transmission_status(struct usart_module *const module)
{
    SercomUsart *const usart_hw = &(module->hw->USART);
    return ((usart_hw->STATUS.reg & SERCOM_USART_STATUS_TXE)? true:false);
}

/** @} */
#endif

#ifdef __cplusplus
}
#endif

/** @} */

/**
* \page asfdoc_sam0_sercom_usart_extra Extra Information for SERCOM USART Driver
*
* \section asfdoc_sam0_sercom_usart_extra_acronyms Acronyms
*
* Below is a table listing the acronyms used in this module, along with their
* intended meanings.
*
* <table>
* <tr>
* <th>Acronym</th>
* <th>Description</th>
* </tr>
* <tr>
* <td>SERCOM</td>
* <td>Serial Communication Interface</td>
* </tr>
* <tr>
* <td>USART</td>
* <td>Universal Synchronous and Asynchronous Serial Receiver and Transmitter</td>
* </tr>
* <tr>
* <td>LSB</td>
* <td>Least Significant Bit</td>
* </tr>
* <tr>
* <td>MSB</td>
* <td>Most Significant Bit</td>
* </tr>
* <tr>
* <td>DMA</td>
* <td>Direct Memory Access</td>
* </tr>
* </table>
*
*
* \section asfdoc_sam0_sercom_usart_extra_dependencies Dependencies
* This driver has the following dependencies:
*
* - \ref asfdoc_sam0_system_pinmux_group "System Pin Multiplexer Driver"
* - \ref asfdoc_sam0_system_clock_group "System clock configuration"
*
*
* \section asfdoc_sam0_sercom_usart_extra_errata Errata
* There are no errata related to this driver.
*
*
* \section asfdoc_sam0_sercom_usart_extra_history Module History
* An overview of the module history is presented in the table below, with
* details on the enhancements and fixes made to the module since its first
* release. The current version of this corresponds to the newest version in
* the table.
*
 * <table>
 *	<tr>
 *		<th>Changelog</th>
 *	</tr>
  *	<tr>
 *		<td>Added new feature as below:
 *          \li LIN master
 *          \li RS485
 *	</tr>
 *	<tr>
 *		<td>Added new feature as below:
 *          \li Oversample
 *          \li Buffer overflow notification
 *          \li Irda
 *          \li Lin slave
 *          \li Start frame detection
 *          \li Hardware flow control
 *          \li Collision detection
 *          \li DMA support </td>
 *	</tr>
 *	<tr>
 *		<td>\li Added new \c transmitter_enable and \c receiver_enable Boolean
 *              values to \c struct usart_config
 *          \li Altered \c usart_write_* and usart_read_* functions to abort with
 *              an error code if the relevant transceiver is not enabled
 *          \li Fixed \c usart_write_buffer_wait() and \c usart_read_buffer_wait()
 *              not aborting correctly when a timeout condition occurs</td>
 *	</tr>
 *	<tr>
 *		<td>Initial Release</td>
 *	</tr>
 * </table>
*/

/**
 * \page asfdoc_sam0_sercom_usart_exqsg Examples for SERCOM USART Driver
 *
 * This is a list of the available Quick Start guides (QSGs) and example
 * applications for \ref asfdoc_sam0_sercom_usart_group. QSGs are simple examples with
 * step-by-step instructions to configure and use this driver in a selection of
 * use cases. Note that QSGs can be compiled as a standalone application or be
 * added to the user application.
 *
 * - \subpage asfdoc_sam0_sercom_usart_basic_use_case
 * \if USART_CALLBACK_MODE
 * - \subpage asfdoc_sam0_sercom_usart_callback_use_case
 * \endif
 * - \subpage asfdoc_sam0_sercom_usart_dma_use_case
 * - \subpage asfdoc_sam0_sercom_usart_lin_use_case
 */

/**
 * \page asfdoc_sam0_sercom_usart_mux_settings SERCOM USART MUX Settings
 *
 * The following lists the possible internal SERCOM module pad function
 * assignments, for the four SERCOM pads when in USART mode. Note that this is
 * in addition to the physical GPIO pin MUX of the device, and can be used in
 * conjunction to optimize the serial data pin-out.
 *
 * When TX and RX are connected to the same pin, the USART will operate in
 * half-duplex mode if both the transmitter and receivers are enabled.
 *
 * \note When RX and XCK are connected to the same pin, the receiver must not
 *       be enabled if the USART is configured to use an external clock.
 *
 *
 * <table>
 *		<tr>
 *			<th>MUX/Pad</th>
 *			<th>PAD 0</th>
 *			<th>PAD 1</th>
 *			<th>PAD 2</th>
 *			<th>PAD 3</th>
 *		</tr>
 *		<tr>
 *			<td>RX_0_TX_0_XCK_1</td>
 *			<td>TX / RX</td>
 *			<td>XCK</td>
 *			<td>-</td>
 *			<td>-</td>
 *		</tr>
 *		<tr>
 *			<td>RX_0_TX_2_XCK_3</td>
 *			<td>RX</td>
 *			<td>-</td>
 *			<td>TX</td>
 *			<td>XCK</td>
 *		</tr>
 *		<tr>
 *			<td>RX_1_TX_0_XCK_1</td>
 *			<td>TX</td>
 *			<td>RX / XCK</td>
 *			<td>-</td>
 *			<td>-</td>
 *		</tr>
 *		<tr>
 *			<td>RX_1_TX_2_XCK_3</td>
 *			<td>-</td>
 *			<td>RX</td>
 *			<td>TX</td>
 *			<td>XCK</td>
 *		</tr>
 *		<tr>
 *			<td>RX_2_TX_0_XCK_1</td>
 *			<td>TX</td>
 *			<td>XCK</td>
 *			<td>RX</td>
 *			<td>-</td>
 *		</tr>
 *		<tr>
 *			<td>RX_2_TX_2_XCK_3</td>
 *			<td>-</td>
 *			<td>-</td>
 *			<td>TX / RX</td>
 *			<td>XCK</td>
 *		</tr>
 *		<tr>
 *			<td>RX_3_TX_0_XCK_1</td>
 *			<td>TX</td>
 *			<td>XCK</td>
 *			<td>-</td>
 *			<td>RX</td>
 *		</tr>
 *		<tr>
 *			<td>RX_3_TX_2_XCK_3</td>
 *			<td>-</td>
 *			<td>-</td>
 *			<td>TX</td>
 *			<td>RX / XCK</td>
 *		</tr>
 * </table>
 *
 * \page asfdoc_sam0_sercom_usart_document_revision_history Document Revision History
 *
 * <table>
 *	<tr>
 *		<th>Doc. Rev.</td>
 *		<th>Date</td>
 *		<th>Comments</td>
 *	</tr>
 *	<tr>
 *		<td>42118F</td>
 *		<td>06/2015</td>
 *		<td>Add support for SAML21, SAMDAx, and SAMC20/C21.</td>
 *	</tr>
 *	<tr>
 *		<td>42118E</td>
 *		<td>12/2014</td>
 *		<td>Add support for SAMR21 and SAMD10/D11.</td>
 *	</tr>
 *	<tr>
 *		<td>42118D</td>
 *		<td>01/2014</td>
 *		<td>Add support for SAMD21.</td>
 *	</tr>
 *	<tr>
 *		<td>42118C</td>
 *		<td>10/2013</td>
 *		<td>Replaced the pad multiplexing documentation with a condensed table.</td>
 *	</tr>
 *	<tr>
 *		<td>42118B</td>
 *		<td>06/2013</td>
 *		<td>Corrected documentation typos.</td>
 *	</tr>
 *	<tr>
 *		<td>42118A</td>
 *		<td>06/2013</td>
 *		<td>Initial release</td>
 *	</tr>
 * </table>
 */
#endif /* USART_H_INCLUDED */