usart.c File Reference

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Detailed Description

MMU example application.

This file gives an example of using the MMU to manage the memory on AVR32 MCUs.

• Compiler: IAR EWAAVR32 and GNU GCC for AVR32
• Supported devices: All AVR32 devices with MMU.
• AppNote: AVR32113 Configuration and Use of the Memory Management Unit

Author:

Atmel Corporation: http://www.atmel.com
Support email: avr32@atmel.com

$Name$

Revision

$RCSfile$

Date

Definition in file usart.c.

#include "usart.h"

Include dependency graph for usart.c:

Go to the source code of this file.

Functions
int	_write_r (struct _reent *ptr, int fd, const void *buf, size_t cnt)
	Function to overload the standard _write_r, makes it possible to use printf() to output data.
int	usart_linit (volatile avr32_usart_t *usart, const struct usart_options_t *opt, const long cpuHz)
	Setup the usart to use the standard RS232 protocol.
int	usart_putchar (volatile avr32_usart_t *usart, const short character)
	Send a character with the usart.
void	usart_reset (volatile avr32_usart_t *usart)
	This function will reset the USART, and disable TX and RX.
static int	usart_set_baudrate (volatile avr32_usart_t *usart, unsigned int baudrate, const long cpuHz)
	This function will calculate a clock divider(CD) and fractional part(FP) that gets the usart as close to a wanted baudrate as possible.

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Function Documentation

int _write_r	(	struct _reent *	ptr,
		int	fd,
		const void *	buf,
		size_t	cnt
	)

Function to overload the standard _write_r, makes it possible to use printf() to output data.

Parameters:

	ptr	not used
	fd	not used
	buf	the buffer to send
	cnt	number of bytes to send

Returns:

Status

Definition at line 252 of file usart.c.

{
    volatile char *msg = (char *) buf;
    volatile int i;

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

    return cnt;
}

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

Setup the usart to use the standard RS232 protocol.

Parameters:

	usart	base address of the usart
	opt	options needed to set up RS232 communcation (see usart_options_t)
	cpuHz	frequency of the selected clock

Returns:

status

Return values:

	USART_OK	on success
	USART_ERROR_ARGUMENT	on wrong arguments

Definition at line 152 of file usart.c.

Referenced by main().

{
    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
	)

Send a character with the usart.

Parameters:

	usart	base address of the usart
	character	character to write

Returns:

status

Return values:

	USART_OK	on success
	USART_TX_BUSY	on timeout

Definition at line 222 of file usart.c.

Referenced by _write_r().

{
    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;
}

void usart_reset

(

volatile avr32_usart_t *

usart

)

This function will reset the USART, and disable TX and RX.

Parameters:

usart

Base address of the usart

Definition at line 56 of file usart.c.

Referenced by usart_linit().

{
    /* 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
	)			[static]

This function will calculate a clock divider(CD) and fractional part(FP) that gets the usart as close to a wanted baudrate as possible.

Parameters:

	usart	base address of the usart
	baudrate	wanted baudrate
	cpuHz	frequency of the selected clock

Returns:

status

Return values:

	USART_OK	on success
	USART_ERROR_ARGUMENT	if wanted baudrate is impossible with given clockspeed

Definition at line 94 of file usart.c.

References USART_ERROR_ARGUMENT, and USART_OK.

Referenced by usart_linit().

{
    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;
}

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