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SAM4S2A USART


ASF Wizard​

  • USART - Serial interface (service): Common API which abstracts the user from directly accessing the register and provides a generic serial interface using USART.
  • PIO - Parallel Input/Output Controller (driver): The Parallel Input/Output Controller manages up to 32 fully programmable input/output lines. Each I/O line may be dedicated as a general-purpose I/O or be assigned to a function of an embedded peripheral. This assures effective optimization of the pins of a product.

src\config\conf_board.h​

#ifndef CONF_BOARD_H
#define CONF_BOARD_H

#define CONSOLE_UART (Usart *)USART0

/** Enable Com Port. */
#define CONF_BOARD_UART_CONSOLE

#endif    // CONF_BOARD_H

src\config\conf_uart_serial.h​

#ifndef CONF_USART_SERIAL_H
#define CONF_USART_SERIAL_H

/* A reference setting for USART */
/** USART Interface */
#define CONF_UART CONSOLE_UART
/** Baudrate setting */
#define CONF_UART_BAUDRATE 115200
/** Character length setting */
#define CONF_UART_CHAR_LENGTH US_MR_CHRL_8_BIT
/** Parity setting */
#define CONF_UART_PARITY US_MR_PAR_NO
/** Stop bits setting */
#define CONF_UART_STOP_BITS US_MR_NBSTOP_1_BIT

#define USART_SERIAL                CONF_UART
#define USART_SERIAL_ID             ID_USART0
#define USART_SERIAL_BAUDRATE       CONF_UART_BAUDRATE
#define USART_SERIAL_CHAR_LENGTH    CONF_UART_CHAR_LENGTH
#define USART_SERIAL_PARITY         CONF_UART_PARITY
#define USART_SERIAL_STOP_BIT       CONF_UART_STOP_BITS
#define USART_SERIAL_IRQ            USART0_IRQn
#define USART_SERIAL_ISR_HANDLER    USART0_Handler
#define USART_SERIAL_RX_BUFFER_SIZE 128
#define USART_SERIAL_TX_BUFFER_SIZE 128

#define PINS_USART0_PIO  PIOA
#define PINS_USART0_ID   USART_SERIAL_ID
#define PINS_USART0_TYPE PIO_PERIPH_A
#define PINS_USART0_ATTR PIO_DEFAULT
#define PINS_USART0_MASK (PIO_PA5A_RXD0 | PIO_PA6A_TXD0)

#endif /* CONF_USART_SERIAL_H_INCLUDED */

Examples​

#include "conf_uart_serial.h"

#include <asf.h>

volatile uint8_t  rx_buffer[USART_SERIAL_RX_BUFFER_SIZE];
volatile uint16_t rx_buffer_tail = 0;
volatile uint16_t rx_buffer_head = 0;

void serial_init(void) {
    pio_configure(
        PINS_USART0_PIO, PINS_USART0_TYPE, PINS_USART0_MASK, PINS_USART0_ATTR);
    pmc_enable_periph_clk(USART_SERIAL_ID);
    sysclk_enable_peripheral_clock(USART_SERIAL_ID);

    const sam_usart_opt_t usart_console_settings
        = {.baudrate     = USART_SERIAL_BAUDRATE,
           .char_length  = USART_SERIAL_CHAR_LENGTH,
           .parity_type  = USART_SERIAL_PARITY,
           .stop_bits    = USART_SERIAL_STOP_BIT,
           .channel_mode = US_MR_CHMODE_NORMAL};
    usart_init_rs232(USART_SERIAL, &usart_console_settings, F_CPU);
    usart_enable_tx(USART_SERIAL);
    usart_enable_rx(USART_SERIAL);

    usart_enable_interrupt(USART_SERIAL, US_IER_RXRDY);
    NVIC_EnableIRQ(USART_SERIAL_IRQ);
}

uint16_t serial_available(void) {
    return (USART_SERIAL_RX_BUFFER_SIZE + rx_buffer_head - rx_buffer_tail)
           % USART_SERIAL_RX_BUFFER_SIZE;
}

char serial_read(void) {
    if(rx_buffer_head == rx_buffer_tail) return 0;
    else {
        uint8_t temp   = rx_buffer[rx_buffer_tail];
        rx_buffer_tail = (rx_buffer_tail + 1) % USART_SERIAL_RX_BUFFER_SIZE;
        return temp;
    }
}

int main(void) {
    sysclk_init();
    board_init();
    /* Insert application code here, after the board has been initialized. */
    wdt_disable(WDT);

    serial_init();

    for(;;) {
        if(serial_available()) { usart_write(USART_SERIAL, serial_read()); }
    }
}

ISR(USART_SERIAL_ISR_HANDLER) {
    if(usart_is_rx_ready(USART_SERIAL)) {
        usart_read(USART_SERIAL, &rx_buffer[rx_buffer_head]);
        rx_buffer_head = (rx_buffer_head + 1) % USART_SERIAL_RX_BUFFER_SIZE;
        if(rx_buffer_head == rx_buffer_tail) {
            rx_buffer_tail = (rx_buffer_tail + 1) % USART_SERIAL_RX_BUFFER_SIZE;
        }
    }
}

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