usart.c

Go to the documentation of this file.

/*This file has been prepared for Doxygen automatic documentation generation.*/
/* Copyright (c) 2006, Atmel Corporation All rights reserved.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY ATMEL ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 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.
 */

#include "usart.h"

void usart_reset(volatile avr32_usart_t * usart)
{
    /* Disable all usart interrupts, interrupts needed should be set
       explicitly on every reset */
    usart->idr = 0xFFFFffff;

    /* Reset mode and other registers that could cause unpredictable
       behaviour after reset */
    usart->mr = 0;
    usart->rtor = 0;
    usart->ttgr = 0;

    /* Shutdown RX and TX (will be reenabled when setup
       is completed successfully), reset status bits and turn
       off DTR and RTS */
    usart->cr = AVR32_USART_CR_RSTRX_MASK|
                AVR32_USART_CR_RSTTX_MASK|
                AVR32_USART_CR_RSTSTA_MASK|
                AVR32_USART_CR_RSTIT_MASK|
                AVR32_USART_CR_RSTNACK_MASK|
                AVR32_USART_CR_DTRDIS_MASK|
                AVR32_USART_CR_RTSDIS_MASK;
}


static int usart_set_baudrate(volatile avr32_usart_t * usart,
        unsigned int baudrate,
        const long cpuHz)
{
    int cd, fp; /* clock divider and fractional part */

    /*
     *             ** BAUDRATE CALCULATION **
     *
     *                 selected clock                       selected clock
     *     baudrate = ----------------   or     baudrate = ----------------
     *                16 x (CD + FP/8)                      8 x (CD + FP/8)
     *
     *       (with 16x oversampling)              (with 8x oversampling)
     */
    if (baudrate > (cpuHz/16)) {
        /* use 8x oversampling */
        usart->mr |= (AVR32_USART_MR_OVER_MASK);
        cd = cpuHz / (8 * baudrate);

        if (cd < 2) {
            /* wanted baudrate is too high */
            return USART_ERROR_ARGUMENT;
        }

        fp = cpuHz / baudrate - 8 * cd;
        usart->brgr = (fp << AVR32_USART_BRGR_FP_OFFSET)
            | (cd << AVR32_USART_BRGR_CD_OFFSET);
    } else {
        /* use 16x oversampling */
        usart->mr &= ~(AVR32_USART_MR_OVER_MASK);
        cd = cpuHz / (16 * baudrate);

        if (cd > 65535) {
            /* wanted baudrate is too low */
            return USART_ERROR_ARGUMENT;
        }

        fp = cpuHz / (2 * baudrate) - 16 * cd;
        usart->brgr = (fp << AVR32_USART_BRGR_FP_OFFSET)
            | (cd << AVR32_USART_BRGR_CD_OFFSET);
    }

    return USART_OK;
}


int usart_linit(volatile avr32_usart_t * usart,
        const struct usart_options_t * opt,
        const long cpuHz)
{
    int retval;

    /* reset the usart and shutdown RX and TX */
    usart_reset(usart);

    /* control input values */
    if (opt == 0) {
        return USART_ERROR_ARGUMENT;
    }
    if (opt->charlength < 5 || opt->charlength > 9) {
        return USART_ERROR_ARGUMENT;
    }
    if (opt->paritytype > 7) {
        return USART_ERROR_ARGUMENT;
    }
    if (opt->stopbits > 2+255) {
        return USART_ERROR_ARGUMENT;
    }
    if (opt->channelmode > 3) {
        return USART_ERROR_ARGUMENT;
    }

    retval = usart_set_baudrate(usart, opt->baudrate, cpuHz);

    if (retval != USART_OK) {
        return retval;
    }

    if (opt->charlength == 9) {
        /* charlength set to 9 bits; MODE9 dominates CHRL */
        usart->mr |= AVR32_USART_MR_MODE9_MASK;
    } else {
        /* CHRL gives the charlength(- 5) when USART_MODE9=0 */
        usart->mr |=
            ((opt->charlength-5)<<AVR32_USART_MR_CHRL_OFFSET);
    }

    usart->mr |= (opt->channelmode<<AVR32_USART_MR_CHMODE_OFFSET)|
                 (opt->paritytype<<AVR32_USART_MR_PAR_OFFSET);

    if (opt->stopbits > 2) {
        /* set two stop bits */
        usart->mr |= (2<<AVR32_USART_MR_NBSTOP_OFFSET);
        /* and a timeguard period gives the rest */
        usart->ttgr = (opt->stopbits-2);
    } else {
        /* insert 1, 1.5 or 2 stop bits */
        usart->mr |= (opt->stopbits<<AVR32_USART_MR_NBSTOP_OFFSET);
    }

    /* enable TX and RX */
    usart->cr |= AVR32_USART_CR_TXEN_MASK|AVR32_USART_CR_RXEN_MASK;

    return USART_OK;
}


int usart_putchar(volatile avr32_usart_t * usart, const short character)
{
    int timeout = USART_DEFAULT_TIMEOUT;

    do {
        --timeout;
    } while ((usart->csr & AVR32_USART_CSR_TXRDY_MASK) == 0 && timeout > 0);

    if (timeout == 0) {
        return USART_TX_BUSY;
    }

    usart->thr = character;

    return USART_OK;
}


/* printf rewrite functions */

int _write_r(struct _reent *ptr, int fd, const void *buf, size_t cnt)
{
    volatile char *msg = (char *) buf;
    volatile int i;

    for (i=0; i < cnt; i++) {
        usart_putchar(&USART_MODULE, *msg++);
    }

    return cnt;
}

---