rt-thread/bsp/samd21/sam_d2x_asflib/sam0/drivers/sercom/usart/usart.c

/**
 * \file
 *
 * \brief SAM SERCOM USART Driver
 *
 * Copyright (C) 2012-2016 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>
 */
#include "usart.h"
#include <pinmux.h>
#if USART_CALLBACK_MODE == true
#  include "usart_interrupt.h"
#endif

/**
 * \internal
 * Set Configuration of the USART module
 */
static enum status_code _usart_set_config(
		struct usart_module *const module,
		const struct usart_config *const config)
{
	/* Sanity check arguments */
	Assert(module);
	Assert(module->hw);

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

	/* Index for generic clock */
	uint32_t sercom_index = _sercom_get_sercom_inst_index(module->hw);
	uint32_t gclk_index   = sercom_index + SERCOM0_GCLK_ID_CORE;

	/* Cache new register values to minimize the number of register writes */
	uint32_t ctrla = 0;
	uint32_t ctrlb = 0;
#ifdef FEATURE_USART_ISO7816
	uint32_t ctrlc = 0;
#endif
	uint16_t baud  = 0;
	uint32_t transfer_mode;

	enum sercom_asynchronous_operation_mode mode = SERCOM_ASYNC_OPERATION_MODE_ARITHMETIC;
	enum sercom_asynchronous_sample_num sample_num = SERCOM_ASYNC_SAMPLE_NUM_16;

#ifdef FEATURE_USART_OVER_SAMPLE
	switch (config->sample_rate) {
		case USART_SAMPLE_RATE_16X_ARITHMETIC:
			mode = SERCOM_ASYNC_OPERATION_MODE_ARITHMETIC;
			sample_num = SERCOM_ASYNC_SAMPLE_NUM_16;
			break;
		case USART_SAMPLE_RATE_8X_ARITHMETIC:
			mode = SERCOM_ASYNC_OPERATION_MODE_ARITHMETIC;
			sample_num = SERCOM_ASYNC_SAMPLE_NUM_8;
			break;
		case USART_SAMPLE_RATE_3X_ARITHMETIC:
			mode = SERCOM_ASYNC_OPERATION_MODE_ARITHMETIC;
			sample_num = SERCOM_ASYNC_SAMPLE_NUM_3;
			break;
		case USART_SAMPLE_RATE_16X_FRACTIONAL:
			mode = SERCOM_ASYNC_OPERATION_MODE_FRACTIONAL;
			sample_num = SERCOM_ASYNC_SAMPLE_NUM_16;
			break;
		case USART_SAMPLE_RATE_8X_FRACTIONAL:
			mode = SERCOM_ASYNC_OPERATION_MODE_FRACTIONAL;
			sample_num = SERCOM_ASYNC_SAMPLE_NUM_8;
			break;
	}
#endif

	/* Set data order, internal muxing, and clock polarity */
	ctrla = (uint32_t)config->data_order |
		(uint32_t)config->mux_setting |
	#ifdef FEATURE_USART_OVER_SAMPLE
		config->sample_adjustment |
		config->sample_rate |
	#endif
	#ifdef FEATURE_USART_IMMEDIATE_BUFFER_OVERFLOW_NOTIFICATION
		(config->immediate_buffer_overflow_notification << SERCOM_USART_CTRLA_IBON_Pos) |
	#endif
		(config->clock_polarity_inverted << SERCOM_USART_CTRLA_CPOL_Pos);

	enum status_code status_code = STATUS_OK;

	transfer_mode = (uint32_t)config->transfer_mode;
#ifdef FEATURE_USART_ISO7816
	if(config->iso7816_config.enabled) {
		transfer_mode = config->iso7816_config.protocol_t;
	}
#endif
	/* Get baud value from mode and clock */
#ifdef FEATURE_USART_ISO7816
	if(config->iso7816_config.enabled) {
		baud = config->baudrate;
	} else {
#endif
	switch (transfer_mode)
	{
		case USART_TRANSFER_SYNCHRONOUSLY:
			if (!config->use_external_clock) {
				status_code = _sercom_get_sync_baud_val(config->baudrate,
						system_gclk_chan_get_hz(gclk_index), &baud);
			}

			break;

		case USART_TRANSFER_ASYNCHRONOUSLY:
			if (config->use_external_clock) {
				status_code =
						_sercom_get_async_baud_val(config->baudrate,
							config->ext_clock_freq, &baud, mode, sample_num);
			} else {
				status_code =
						_sercom_get_async_baud_val(config->baudrate,
							system_gclk_chan_get_hz(gclk_index), &baud, mode, sample_num);
			}

			break;
	}

	/* Check if calculating the baudrate failed */
	if (status_code != STATUS_OK) {
		/* Abort */
		return status_code;
	}
#ifdef FEATURE_USART_ISO7816
	}
#endif

#ifdef FEATURE_USART_IRDA
	if(config->encoding_format_enable) {
		usart_hw->RXPL.reg = config->receive_pulse_length;
	}
#endif

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

	/*Set baud val */
	usart_hw->BAUD.reg = baud;

	/* Set sample mode */
	ctrla |= transfer_mode;

	if (config->use_external_clock == false) {
		ctrla |= SERCOM_USART_CTRLA_MODE(0x1);
	}
	else {
		ctrla |= SERCOM_USART_CTRLA_MODE(0x0);
	}

	/* Set stopbits and enable transceivers */
	ctrlb =  
		#ifdef FEATURE_USART_IRDA
			(config->encoding_format_enable << SERCOM_USART_CTRLB_ENC_Pos) |
		#endif
		#ifdef FEATURE_USART_START_FRAME_DECTION
			(config->start_frame_detection_enable << SERCOM_USART_CTRLB_SFDE_Pos) |
		#endif
		#ifdef FEATURE_USART_COLLISION_DECTION
			(config->collision_detection_enable << SERCOM_USART_CTRLB_COLDEN_Pos) |
		#endif
			(config->receiver_enable << SERCOM_USART_CTRLB_RXEN_Pos) |
			(config->transmitter_enable << SERCOM_USART_CTRLB_TXEN_Pos);

#ifdef FEATURE_USART_ISO7816
	if(config->iso7816_config.enabled) {
		ctrla |= SERCOM_USART_CTRLA_FORM(0x07);
		if (config->iso7816_config.enable_inverse) {
			ctrla |= SERCOM_USART_CTRLA_TXINV | SERCOM_USART_CTRLA_RXINV;
		}
		ctrlb |=  USART_CHARACTER_SIZE_8BIT;
		
		switch(config->iso7816_config.protocol_t) {
			case ISO7816_PROTOCOL_T_0:
				ctrlb |= (uint32_t)config->stopbits;	
				ctrlc |= SERCOM_USART_CTRLC_GTIME(config->iso7816_config.guard_time) | \
						(config->iso7816_config.inhibit_nack) | \
						(config->iso7816_config.successive_recv_nack) | \
						SERCOM_USART_CTRLC_MAXITER(config->iso7816_config.max_iterations);
				break;	
			case ISO7816_PROTOCOL_T_1:
				ctrlb |= USART_STOPBITS_1;
				break;		
		}
	} else {
#endif
	ctrlb |= (uint32_t)config->stopbits;
	ctrlb |= (uint32_t)config->character_size;
	/* Check parity mode bits */
	if (config->parity != USART_PARITY_NONE) {
		ctrla |= SERCOM_USART_CTRLA_FORM(1);
		ctrlb |= config->parity;
	} else {
#ifdef FEATURE_USART_LIN_SLAVE
		if(config->lin_slave_enable) {
			ctrla |= SERCOM_USART_CTRLA_FORM(0x4);
		} else {
			ctrla |= SERCOM_USART_CTRLA_FORM(0);
		}
#else
		ctrla |= SERCOM_USART_CTRLA_FORM(0);
#endif
	}
#ifdef FEATURE_USART_ISO7816
	}
#endif

#ifdef FEATURE_USART_LIN_MASTER
	usart_hw->CTRLC.reg = ((usart_hw->CTRLC.reg) & SERCOM_USART_CTRLC_GTIME_Msk)
						| config->lin_header_delay
						| config->lin_break_length;

	if (config->lin_node != LIN_INVALID_MODE) {
		ctrla &= ~(SERCOM_USART_CTRLA_FORM(0xf));
		ctrla |= config->lin_node;
	}
#endif

	/* Set whether module should run in standby. */
	if (config->run_in_standby || system_is_debugger_present()) {
		ctrla |= SERCOM_USART_CTRLA_RUNSTDBY;
	}

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

	/* Write configuration to CTRLB */
	usart_hw->CTRLB.reg = ctrlb;

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

	/* Write configuration to CTRLA */
	usart_hw->CTRLA.reg = ctrla;

#ifdef FEATURE_USART_RS485
	if ((usart_hw->CTRLA.reg & SERCOM_USART_CTRLA_FORM_Msk) != \
		SERCOM_USART_CTRLA_FORM(0x07)) {
		usart_hw->CTRLC.reg &= ~(SERCOM_USART_CTRLC_GTIME(0x7));
		usart_hw->CTRLC.reg |= SERCOM_USART_CTRLC_GTIME(config->rs485_guard_time);
	}
#endif

#ifdef FEATURE_USART_ISO7816
	if(config->iso7816_config.enabled) {
		_usart_wait_for_sync(module);
		usart_hw->CTRLC.reg = ctrlc;
	}
#endif

	return STATUS_OK;
}

/**
 * \brief Initializes the device
 *
 * Initializes the USART device based on the setting specified in the
 * configuration struct.
 *
 * \param[out] module  Pointer to USART device
 * \param[in]  hw      Pointer to USART hardware instance
 * \param[in]  config  Pointer to configuration struct
 *
 * \return Status of the initialization.
 *
 * \retval STATUS_OK                       The initialization was successful
 * \retval STATUS_BUSY                     The USART module is busy
 *                                         resetting
 * \retval STATUS_ERR_DENIED               The USART has not been disabled in
 *                                         advance of initialization
 * \retval STATUS_ERR_INVALID_ARG          The configuration struct contains
 *                                         invalid configuration
 * \retval STATUS_ERR_ALREADY_INITIALIZED  The SERCOM instance has already been
 *                                         initialized with different clock
 *                                         configuration
 * \retval STATUS_ERR_BAUD_UNAVAILABLE     The BAUD rate given by the
 *                                         configuration
 *                                         struct cannot be reached with
 *                                         the current clock configuration
 */
enum status_code usart_init(
		struct usart_module *const module,
		Sercom *const hw,
		const struct usart_config *const config)
{
	/* Sanity check arguments */
	Assert(module);
	Assert(hw);
	Assert(config);

	enum status_code status_code = STATUS_OK;

	/* Assign module pointer to software instance struct */
	module->hw = hw;

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

	uint32_t sercom_index = _sercom_get_sercom_inst_index(module->hw);
	uint32_t pm_index, gclk_index; 
#if (SAML22) || (SAMC20) 
	pm_index	= sercom_index + MCLK_APBCMASK_SERCOM0_Pos;
	gclk_index	= sercom_index + SERCOM0_GCLK_ID_CORE;
#elif (SAML21) || (SAMR30)
	if (sercom_index == 5) {
		pm_index     = MCLK_APBDMASK_SERCOM5_Pos;
		gclk_index   = SERCOM5_GCLK_ID_CORE;
	} else {
		pm_index     = sercom_index + MCLK_APBCMASK_SERCOM0_Pos;
		gclk_index   = sercom_index + SERCOM0_GCLK_ID_CORE;
	}
#elif (SAMC21)
	pm_index	= sercom_index + MCLK_APBCMASK_SERCOM0_Pos;
	
	if (sercom_index == 5){
		gclk_index	= SERCOM5_GCLK_ID_CORE;
    } else {
    	gclk_index	= sercom_index + SERCOM0_GCLK_ID_CORE;
    }
#else
	pm_index     = sercom_index + PM_APBCMASK_SERCOM0_Pos;
	gclk_index   = sercom_index + SERCOM0_GCLK_ID_CORE;
#endif

	if (usart_hw->CTRLA.reg & SERCOM_USART_CTRLA_SWRST) {
		/* The module is busy resetting itself */
		return STATUS_BUSY;
	}

	if (usart_hw->CTRLA.reg & SERCOM_USART_CTRLA_ENABLE) {
		/* Check the module is enabled */
		return STATUS_ERR_DENIED;
	}

	/* Turn on module in PM */
#if (SAML21) || (SAMR30)
	if (sercom_index == 5) {
		system_apb_clock_set_mask(SYSTEM_CLOCK_APB_APBD, 1 << pm_index);
	} else {
		system_apb_clock_set_mask(SYSTEM_CLOCK_APB_APBC, 1 << pm_index);	
	}
#else
	system_apb_clock_set_mask(SYSTEM_CLOCK_APB_APBC, 1 << pm_index);
#endif

	/* Set up the GCLK for the module */
	struct system_gclk_chan_config gclk_chan_conf;
	system_gclk_chan_get_config_defaults(&gclk_chan_conf);
	gclk_chan_conf.source_generator = config->generator_source;
	system_gclk_chan_set_config(gclk_index, &gclk_chan_conf);
	system_gclk_chan_enable(gclk_index);
	sercom_set_gclk_generator(config->generator_source, false);

	/* Set character size */
	module->character_size = config->character_size;

	/* Set transmitter and receiver status */
	module->receiver_enabled = config->receiver_enable;
	module->transmitter_enabled = config->transmitter_enable;

#ifdef FEATURE_USART_LIN_SLAVE
	module->lin_slave_enabled = config->lin_slave_enable;
#endif
#ifdef FEATURE_USART_START_FRAME_DECTION
	module->start_frame_detection_enabled = config->start_frame_detection_enable;
#endif
#ifdef FEATURE_USART_ISO7816
	module->iso7816_mode_enabled = config->iso7816_config.enabled;
#endif
	/* Set configuration according to the config struct */
	status_code = _usart_set_config(module, config);
	if(status_code != STATUS_OK) {
		return status_code;
	}

	struct system_pinmux_config pin_conf;
	system_pinmux_get_config_defaults(&pin_conf);
	pin_conf.direction = SYSTEM_PINMUX_PIN_DIR_INPUT;
	pin_conf.input_pull = SYSTEM_PINMUX_PIN_PULL_NONE;

	uint32_t pad_pinmuxes[] = {
			config->pinmux_pad0, config->pinmux_pad1,
			config->pinmux_pad2, config->pinmux_pad3
		};

	/* Configure the SERCOM pins according to the user configuration */
	for (uint8_t pad = 0; pad < 4; pad++) {
		uint32_t current_pinmux = pad_pinmuxes[pad];

		if (current_pinmux == PINMUX_DEFAULT) {
			current_pinmux = _sercom_get_default_pad(hw, pad);
		}

		if (current_pinmux != PINMUX_UNUSED) {
			pin_conf.mux_position = current_pinmux & 0xFFFF;
			system_pinmux_pin_set_config(current_pinmux >> 16, &pin_conf);
		}
	}

#if USART_CALLBACK_MODE == true
	/* Initialize parameters */
	for (uint32_t i = 0; i < USART_CALLBACK_N; i++) {
		module->callback[i]            = NULL;
	}

	module->tx_buffer_ptr              = NULL;
	module->rx_buffer_ptr              = NULL;
	module->remaining_tx_buffer_length = 0x0000;
	module->remaining_rx_buffer_length = 0x0000;
	module->callback_reg_mask          = 0x00;
	module->callback_enable_mask       = 0x00;
	module->rx_status                  = STATUS_OK;
	module->tx_status                  = STATUS_OK;

	/* Set interrupt handler and register USART software module struct in
	 * look-up table */
	uint8_t instance_index = _sercom_get_sercom_inst_index(module->hw);
	_sercom_set_handler(instance_index, _usart_interrupt_handler);
	_sercom_instances[instance_index] = module;
#endif

	return status_code;
}

/**
 * \brief Transmit a character via the USART
 *
 * This blocking function will transmit a single character via the
 * USART.
 *
 * \param[in]  module   Pointer to the software instance struct
 * \param[in]  tx_data  Data to transfer
 *
 * \return Status of the operation.
 * \retval STATUS_OK         If the operation was completed
 * \retval STATUS_BUSY       If the operation was not completed, due to the USART
 *                           module being busy
 * \retval STATUS_ERR_DENIED If the transmitter is not enabled
 */
enum status_code usart_write_wait(
		struct usart_module *const module,
		const uint16_t tx_data)
{
	/* Sanity check arguments */
	Assert(module);
	Assert(module->hw);

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

	/* Check that the transmitter is enabled */
	if (!(module->transmitter_enabled)) {
		return STATUS_ERR_DENIED;
	}

#if USART_CALLBACK_MODE == true
	/* Check if the USART is busy doing asynchronous operation. */
	if (module->remaining_tx_buffer_length > 0) {
		return STATUS_BUSY;
	}

#else
	/* Check if USART is ready for new data */
	if (!(usart_hw->INTFLAG.reg & SERCOM_USART_INTFLAG_DRE)) {
		/* Return error code */
		return STATUS_BUSY;
	}
#endif

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

	/* Write data to USART module */
	usart_hw->DATA.reg = tx_data;

	while (!(usart_hw->INTFLAG.reg & SERCOM_USART_INTFLAG_TXC)) {
		/* Wait until data is sent */
	}

	return STATUS_OK;
}

/**
 * \brief Receive a character via the USART
 *
 * This blocking function will receive a character via the USART.
 *
 * \param[in]   module   Pointer to the software instance struct
 * \param[out]  rx_data  Pointer to received data
 *
 * \return Status of the operation.
 * \retval STATUS_OK                If the operation was completed
 * \retval STATUS_BUSY              If the operation was not completed,
 *                                  due to the USART module being busy
 * \retval STATUS_ERR_BAD_FORMAT    If the operation was not completed,
 *                                  due to configuration mismatch between USART
 *                                  and the sender
 * \retval STATUS_ERR_BAD_OVERFLOW  If the operation was not completed,
 *                                  due to the baudrate being too low or the
 *                                  system frequency being too high
 * \retval STATUS_ERR_BAD_DATA      If the operation was not completed, due to
 *                                  data being corrupted
 * \retval STATUS_ERR_DENIED        If the receiver is not enabled
 */
enum status_code usart_read_wait(
		struct usart_module *const module,
		uint16_t *const rx_data)
{
	/* Sanity check arguments */
	Assert(module);
	Assert(module->hw);

	/* Error variable */
	uint8_t error_code;

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

	/* Check that the receiver is enabled */
	if (!(module->receiver_enabled)) {
		return STATUS_ERR_DENIED;
	}

#if USART_CALLBACK_MODE == true
	/* Check if the USART is busy doing asynchronous operation. */
	if (module->remaining_rx_buffer_length > 0) {
		return STATUS_BUSY;
	}
#endif

	/* Check if USART has new data */
	if (!(usart_hw->INTFLAG.reg & SERCOM_USART_INTFLAG_RXC)) {
		/* Return error code */
		return STATUS_BUSY;
	}

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

	/* Read out the status code and mask away all but the 3 LSBs*/
	error_code = (uint8_t)(usart_hw->STATUS.reg & SERCOM_USART_STATUS_MASK);

	/* Check if an error has occurred during the receiving */
	if (error_code) {
		/* Check which error occurred */
		if (error_code & SERCOM_USART_STATUS_FERR) {
			/* Clear flag by writing a 1 to it and
			 * return with an error code */
			usart_hw->STATUS.reg = SERCOM_USART_STATUS_FERR;

			return STATUS_ERR_BAD_FORMAT;
		} else if (error_code & SERCOM_USART_STATUS_BUFOVF) {
			/* Clear flag by writing a 1 to it and
			 * return with an error code */
			usart_hw->STATUS.reg = SERCOM_USART_STATUS_BUFOVF;

			return STATUS_ERR_OVERFLOW;
		} else if (error_code & SERCOM_USART_STATUS_PERR) {
			/* Clear flag by writing a 1 to it and
			 * return with an error code */
			usart_hw->STATUS.reg = SERCOM_USART_STATUS_PERR;

			return STATUS_ERR_BAD_DATA;
		}
#ifdef FEATURE_USART_LIN_SLAVE
		else if (error_code & SERCOM_USART_STATUS_ISF) {
			/* Clear flag by writing 1 to it  and
			 *  return with an error code */
			usart_hw->STATUS.reg = SERCOM_USART_STATUS_ISF;

			return STATUS_ERR_PROTOCOL;
		}
#endif
#ifdef FEATURE_USART_COLLISION_DECTION
		else if (error_code & SERCOM_USART_STATUS_COLL) {
			/* Clear flag by writing 1 to it
			 *  return with an error code */
			usart_hw->STATUS.reg = SERCOM_USART_STATUS_COLL;

			return STATUS_ERR_PACKET_COLLISION;
		}
#endif
	}

	/* Read data from USART module */
	*rx_data = usart_hw->DATA.reg;

	return STATUS_OK;
}

/**
 * \brief Transmit a buffer of characters via the USART
 *
 * This blocking function will transmit a block of \c length characters
 * via the USART.
 *
 * \note Using this function in combination with the interrupt (\c _job) functions is
 *       not recommended as it has no functionality to check if there is an
 *       ongoing interrupt driven operation running or not.
 *
 * \param[in]  module   Pointer to USART software instance struct
 * \param[in]  tx_data  Pointer to data to transmit
 * \param[in]  length   Number of characters to transmit
 *
 * \note If using 9-bit data, the array that *tx_data point to should be defined 
 *       as uint16_t array and should be casted to uint8_t* pointer. Because it 
 *       is an address pointer, the highest byte is not discarded. For example:
 *   \code
          #define TX_LEN 3
          uint16_t tx_buf[TX_LEN] = {0x0111, 0x0022, 0x0133};
          usart_write_buffer_wait(&module, (uint8_t*)tx_buf, TX_LEN);
    \endcode
 *
 * \return Status of the operation.
 * \retval STATUS_OK              If operation was completed
 * \retval STATUS_ERR_INVALID_ARG If operation was not completed, due to invalid
 *                                arguments
 * \retval STATUS_ERR_TIMEOUT     If operation was not completed, due to USART
 *                                module timing out
 * \retval STATUS_ERR_DENIED      If the transmitter is not enabled
 */
enum status_code usart_write_buffer_wait(
		struct usart_module *const module,
		const uint8_t *tx_data,
		uint16_t length)
{
	/* Sanity check arguments */
	Assert(module);
	Assert(module->hw);

	/* Check if the buffer length is valid */
	if (length == 0) {
		return STATUS_ERR_INVALID_ARG;
	}

	/* Check that the transmitter is enabled */
	if (!(module->transmitter_enabled)) {
		return STATUS_ERR_DENIED;
	}

	/* 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);

	uint16_t tx_pos = 0;

	/* Blocks while buffer is being transferred */
	while (length--) {
		/* Wait for the USART to be ready for new data and abort
		* operation if it doesn't get ready within the timeout*/
		for (uint32_t i = 0; i <= USART_TIMEOUT; i++) {
			if (usart_hw->INTFLAG.reg & SERCOM_USART_INTFLAG_DRE) {
				break;
			} else if (i == USART_TIMEOUT) {
				return STATUS_ERR_TIMEOUT;
			}
		}

		/* Data to send is at least 8 bits long */
		uint16_t data_to_send = tx_data[tx_pos++];

		/* Check if the character size exceeds 8 bit */
		if (module->character_size == USART_CHARACTER_SIZE_9BIT) {
			data_to_send |= (tx_data[tx_pos++] << 8);
		}

		/* Send the data through the USART module */
		usart_write_wait(module, data_to_send);
	}

	/* Wait until Transmit is complete or timeout */
	for (uint32_t i = 0; i <= USART_TIMEOUT; i++) {
		if (usart_hw->INTFLAG.reg & SERCOM_USART_INTFLAG_TXC) {
			break;
		} else if (i == USART_TIMEOUT) {
			return STATUS_ERR_TIMEOUT;
		}
	}

	return STATUS_OK;
}

/**
 * \brief Receive a buffer of \c length characters via the USART
 *
 * This blocking function will receive a block of \c length characters
 * via the USART.
 *
 * \note Using this function in combination with the interrupt (\c *_job)
 *       functions is not recommended as it has no functionality to check if
 *       there is an ongoing interrupt driven operation running or not.
 *
 * \param[in]  module   Pointer to USART software instance struct
 * \param[out] rx_data  Pointer to receive buffer
 * \param[in]  length   Number of characters to receive
 *
 * \note If using 9-bit data, the array that *rx_data point to should be defined 
 *       as uint16_t array and should be casted to uint8_t* pointer. Because it 
 *       is an address pointer, the highest byte is not discarded. For example:
 *   \code
          #define RX_LEN 3
          uint16_t rx_buf[RX_LEN] = {0x0,};
          usart_read_buffer_wait(&module, (uint8_t*)rx_buf, RX_LEN);
    \endcode
 *
 * \return Status of the operation.
 * \retval STATUS_OK                If operation was completed
 * \retval STATUS_ERR_INVALID_ARG   If operation was not completed, due to an
 *                                  invalid argument being supplied
 * \retval STATUS_ERR_TIMEOUT       If operation was not completed, due
 *                                  to USART module timing out
 * \retval STATUS_ERR_BAD_FORMAT    If the operation was not completed,
 *                                  due to a configuration mismatch
 *                                  between USART and the sender
 * \retval STATUS_ERR_BAD_OVERFLOW  If the operation was not completed,
 *                                  due to the baudrate being too low or the
 *                                  system frequency being too high
 * \retval STATUS_ERR_BAD_DATA      If the operation was not completed, due
 *                                  to data being corrupted
 * \retval STATUS_ERR_DENIED        If the receiver is not enabled
 */
enum status_code usart_read_buffer_wait(
		struct usart_module *const module,
		uint8_t *rx_data,
		uint16_t length)
{
	/* Sanity check arguments */
	Assert(module);
	Assert(module->hw);

	/* Check if the buffer length is valid */
	if (length == 0) {
		return STATUS_ERR_INVALID_ARG;
	}

	/* Check that the receiver is enabled */
	if (!(module->receiver_enabled)) {
		return STATUS_ERR_DENIED;
	}

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

	uint16_t rx_pos = 0;

	/* Blocks while buffer is being received */
	while (length--) {
		/* Wait for the USART to have new data and abort operation if it
		 * doesn't get ready within the timeout*/
		for (uint32_t i = 0; i <= USART_TIMEOUT; i++) {
			if (usart_hw->INTFLAG.reg & SERCOM_USART_INTFLAG_RXC) {
				break;
			} else if (i == USART_TIMEOUT) {
				return STATUS_ERR_TIMEOUT;
			}
		}

		enum status_code retval;
		uint16_t received_data = 0;

		retval = usart_read_wait(module, &received_data);

		if (retval != STATUS_OK) {
			/* Overflow, abort */
			return retval;
		}

		/* Read value will be at least 8-bits long */
		rx_data[rx_pos++] = received_data;

		/* If 9-bit data, write next received byte to the buffer */
		if (module->character_size == USART_CHARACTER_SIZE_9BIT) {
			rx_data[rx_pos++] = (received_data >> 8);
		}
	}

	return STATUS_OK;
}