bacnet_stack/ports/atmega328/rs485.c

/**
 * @brief The module handles sending data out the RS-485 port
 * and handles receiving data from the RS-485 port.
 * @author Steve Karg <skarg@users.sourceforge.net>
 * @date 2007
 * @copyright SPDX-License-Identifier: MIT
 */
#include <stddef.h>
#include <stdint.h>
#include <stdbool.h>
#include <stdlib.h>
#include <stdio.h>

/* This file has been customized for use with ATMEGA168 */
#include "hardware.h"
#include "rs485.h"
#include "bacnet/basic/sys/mstimer.h"

/* baud rate */
static uint32_t RS485_Baud = 9600;
/* amount of silence on the wire */
static struct mstimer Silence_Timer;

/* Public access to the Silence Timer */
unsigned long RS485_Timer_Silence(void)
{
    return mstimer_elapsed(&Silence_Timer);
}

/* Public reset of the Silence Timer */
void RS485_Timer_Silence_Reset(void)
{
    mstimer_set(&Silence_Timer, 0);
}

/****************************************************************************
 * DESCRIPTION: Initializes the RS485 hardware and variables, and starts in
 *              receive mode.
 * RETURN:      none
 * ALGORITHM:   none
 * NOTES:       none
 *****************************************************************************/
void RS485_Initialize(void)
{
    /* enable Transmit and Receive */
    UCSR0B = _BV(TXEN0) | _BV(RXEN0);

    /* Set USART Control and Status Register n C */
    /* Asynchronous USART 8-bit data, No parity, 1 stop */
    /* Set USART Mode Select: UMSELn1 UMSELn0 = 00 for Asynchronous USART */
    /* Set Parity Mode:  UPMn1 UPMn0 = 00 for Parity Disabled */
    /* Set Stop Bit Select: USBSn = 0 for 1 stop bit */
    /* Set Character Size: UCSZn2 UCSZn1 UCSZn0 = 011 for 8-bit */
    /* Clock Polarity: UCPOLn = 0 when asynchronous mode is used. */
    UCSR0C = _BV(UCSZ01) | _BV(UCSZ00);
    /* Clear Power Reduction USART0 */
    BIT_CLEAR(PRR, PRUSART0);
    /* Use port PD2 for RTS - enable and disable of Transceiver Tx/Rx */
    /* Set port bit as Output - initially receiving */
    BIT_CLEAR(PORTD, PD2);
    BIT_SET(DDRD, DDD2);

    return;
}

/****************************************************************************
 * DESCRIPTION: Returns the baud rate that we are currently running at
 * RETURN:      none
 * ALGORITHM:   none
 * NOTES:       none
 *****************************************************************************/
uint32_t RS485_Get_Baud_Rate(void)
{
    return RS485_Baud;
}

/**
 * @brief Converts kili-baud to baud
 * @param baud_k - baud rate in approximate kilobaud
 * @return: baud rate in bps
 */
uint32_t RS485_Baud_Rate_From_Kilo(uint8_t baud_k)
{
    uint32_t baud = 0;

    if (baud_k == 255) {
        baud = 38400;
    } else if (baud_k >= 115) {
        baud = 115200;
    } else if (baud_k >= 76) {
        baud = 76800;
    } else if (baud_k >= 57) {
        baud = 57600;
    } else if (baud_k >= 38) {
        baud = 38400;
    } else if (baud_k >= 19) {
        baud = 19200;
    } else if (baud_k >= 9) {
        baud = 9600;
    } else {
        baud = 38400;
    }

    return baud;
}

/****************************************************************************
 * DESCRIPTION: Sets the baud rate for the chip USART
 * RETURN:      true if valid baud rate
 * ALGORITHM:   none
 * NOTES:       none
 *****************************************************************************/
bool RS485_Set_Baud_Rate(uint32_t baud)
{
    bool valid = true;

    switch (baud) {
        case 9600:
        case 19200:
        case 38400:
        case 57600:
        case 76800:
        case 115200:
            RS485_Baud = baud;
            /* 2x speed mode */
            BIT_SET(UCSR0A, U2X0);
            /* configure baud rate */
            UBRR0 = (F_CPU / (8UL * RS485_Baud)) - 1;
            break;
        default:
            valid = false;
            break;
    }

    return valid;
}

/****************************************************************************
 * DESCRIPTION: Enable or disable the transmitter
 * RETURN:      none
 * ALGORITHM:   none
 * NOTES:       none
 *****************************************************************************/
void RS485_Transmitter_Enable(bool enable)
{
    if (enable) {
        BIT_SET(PORTD, PD2);
    } else {
        BIT_CLEAR(PORTD, PD2);
    }
}

/****************************************************************************
 * DESCRIPTION: Waits on the SilenceTimer for 40 bits.
 * RETURN:      none
 * ALGORITHM:   none
 * NOTES:       none
 *****************************************************************************/
void RS485_Turnaround_Delay(void)
{
    uint8_t nbytes = 4;

    RS485_Transmitter_Enable(false);
    while (nbytes) {
        while (!BIT_CHECK(UCSR0A, UDRE0)) {
            /* do nothing - wait until Tx buffer is empty */
        }
        /* Send the data byte */
        UDR0 = 0xff;
        nbytes--;
    }
    /* was the frame sent? */
    while (!BIT_CHECK(UCSR0A, TXC0)) {
        /* do nothing - wait until the entire frame in the
           Transmit Shift Register has been shifted out */
    }
    /* Clear the Transmit Complete flag by writing a one to it. */
    BIT_SET(UCSR0A, TXC0);
}

/**
 * @brief Send some data and wait until it is sent
 * @param buffer - data to send
 * @param nbytes - number of bytes of data
 */
void RS485_Send_Data(const uint8_t *buffer, uint16_t nbytes)
{
    while (nbytes) {
        while (!BIT_CHECK(UCSR0A, UDRE0)) {
            /* do nothing - wait until Tx buffer is empty */
        }
        /* Send the data byte */
        UDR0 = *buffer;
        buffer++;
        nbytes--;
    }
    /* was the frame sent? */
    while (!BIT_CHECK(UCSR0A, TXC0)) {
        /* do nothing - wait until the entire frame in the
           Transmit Shift Register has been shifted out */
    }
    /* Clear the Transmit Complete flag by writing a one to it. */
    BIT_SET(UCSR0A, TXC0);
    /* per MSTP spec, sort of */
    RS485_Timer_Silence_Reset();
}

/****************************************************************************
 * DESCRIPTION: Return true if a framing or overrun error is present
 * RETURN:      true if error
 * ALGORITHM:   autobaud - if there are a lot of errors, switch baud rate
 * NOTES:       Clears any error flags.
 *****************************************************************************/
bool RS485_ReceiveError(void)
{
    bool ReceiveError = false;
    volatile uint8_t dummy_data;

    /* check for framing error */
#if 0
    if (BIT_CHECK(UCSR0A, FE0)) {
        /* FIXME: how do I clear the error flags? */
        BITMASK_CLEAR(UCSR0A, (_BV(FE0) | _BV(DOR0) | _BV(UPE0)));
        ReceiveError = true;
    }
#endif
    /* check for overrun error */
    if (BIT_CHECK(UCSR0A, DOR0)) {
        /* flush the receive buffer */
        do {
            dummy_data = UDR0;
        } while (BIT_CHECK(UCSR0A, RXC0));
        ReceiveError = true;
    }
    (void)dummy_data;

    return ReceiveError;
}

/****************************************************************************
 * DESCRIPTION: Return true if data is available
 * RETURN:      true if data is available, with the data in the parameter set
 * ALGORITHM:   none
 * NOTES:       none
 *****************************************************************************/
bool RS485_DataAvailable(uint8_t *data)
{
    bool DataAvailable = false;

    /* check for data */
    if (BIT_CHECK(UCSR0A, RXC0)) {
        *data = UDR0;
        DataAvailable = true;
    }

    return DataAvailable;
}

#ifdef TEST_RS485
int main(void)
{
    unsigned i = 0;
    uint8_t DataRegister;

    RS485_Set_Baud_Rate(38400);
    RS485_Initialize();
    /* receive task */
    for (;;) {
        if (RS485_ReceiveError()) {
            fprintf(stderr, "ERROR ");
        } else if (RS485_DataAvailable(&DataRegister)) {
            fprintf(stderr, "%02X ", DataRegister);
        }
    }
}
#endif /* TEST_RS485 */