mcp2515_send_message.c

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// ----------------------------------------------------------------------------
/*
 * Copyright (c) 2007 Fabian Greif, Roboterclub Aachen e.V.
 *  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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``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 DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS 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.
 *
 * $Id: mcp2515_send_message.c 7224 2009-01-25 20:19:32Z fabian $
 */
// ----------------------------------------------------------------------------
 
#include "mcp2515_private.h"
#ifdef  SUPPORT_FOR_MCP2515__
 
#include <util/delay.h>
 
// ----------------------------------------------------------------------------
uint8_t mcp2515_send_message(const can_t *msg)
{
        // Status des MCP2515 auslesen
        uint8_t status = mcp2515_read_status(SPI_READ_STATUS);
        
        /* Statusbyte:
         *
         * Bit  Funktion
         *  2   TXB0CNTRL.TXREQ
         *  4   TXB1CNTRL.TXREQ
         *  6   TXB2CNTRL.TXREQ
         */
        uint8_t address;
        if (_bit_is_clear(status, 2)) {
                address = 0x00;
        }
        else if (_bit_is_clear(status, 4)) {
                address = 0x02;
        } 
        else if (_bit_is_clear(status, 6)) {
                address = 0x04;
        }
        else {
                // Alle Puffer sind belegt,
                // Nachricht kann nicht verschickt werden
                return 0;
        }
        
        RESET(MCP2515_CS);
        spi_putc(SPI_WRITE_TX | address);
        #if SUPPORT_EXTENDED_CANID
                mcp2515_write_id(&msg->id, msg->flags.extended);
        #else
                mcp2515_write_id(&msg->id);
        #endif
        uint8_t length = msg->length & 0x0f;
        
        // Ist die Nachricht ein "Remote Transmit Request" ?
        if (msg->flags.rtr)
        {
                // Ein RTR hat zwar eine Laenge,
                // enthaelt aber keine Daten
                
                // Nachrichten Laenge + RTR einstellen
                spi_putc((1<<RTR) | length);
        }
        else
        {
                // Nachrichten Laenge einstellen
                spi_putc(length);
                
                // Daten
                for (uint8_t i=0;i<length;i++) {
                        spi_putc(msg->data[i]);
                }
        }
        SET(MCP2515_CS);
        
        _delay_us(1);
        
        // CAN Nachricht verschicken
        // die letzten drei Bit im RTS Kommando geben an welcher
        // Puffer gesendet werden soll.
        RESET(MCP2515_CS);
        address = (address == 0) ? 1 : address;
        spi_putc(SPI_RTS | address);
        SET(MCP2515_CS);
        
        CAN_INDICATE_TX_TRAFFIC_FUNCTION;
        
        return address;
}
 
#endif  // SUPPORT_FOR_MCP2515__