AVR Freaks

I want a interrupt driven RX and a polled TX in my system.

    CANIE2 = 1;       //Enable interrupt on Mob 0
…..
    CANGIE = (1 << ENIT) | (1 << ENRX) | (1 << ENTX);

    if((  CANCDMOB & 0b11000000) && ( (CANSTMOB & 0x40) ==0))

    if ((CANSTMOB & (1 << TXOK)) == 0)

    if ((CANEN & (1 << ENMOB1)) != 0)		// Is MOb 1 still busy and in use?

    msg.id <<= 3;          //write 29 Bit identifier
    CANIDT4 = (unsigned char) (msg.id&0xF8);
    CANIDT3 = (unsigned char) (msg.id>>8);
    CANIDT2 = (unsigned char) (msg.id>>16);
    CANIDT1 = (unsigned char) (msg.id>>24);

    CANIDT = (msg.id << 3);	// This leaves RTRTAG, RB1TAG and RB0TAG all zero.
// I assume msg.id is an unsigned long (uint32_t).

    msg.id = 0;
    msg.id |= ((unsigned long) CANIDT1<<24);   //get identifier
    msg.id |= ((unsigned long) CANIDT2<<16);
    msg.id |= ((unsigned long) CANIDT3<<8);
    msg.id |= (CANIDT4 & 0xF8);
    msg.id >>= 3;

    msg.id = (CANIDT >> 3);

    msg.len = CANCDMOB & 0x08;

    CANSTMOB = 0;               //clear interrupt flag

void can_init (void)
{
   uint8_t mob;

   CANGCON = (1 << SWRES);     // Reset the CAN cntr hw

// Should can_tail and can_head be initialized here since the CAN hardware is also just initialized?

   for (mob = 0; mob < AT90CAN_MOBS; mob++)
   {
    CANPAGE = (mob << MOBNB0);   // Set the MOb page
    CANCDMOB = MOB_DIS_CMD;           // Set each MOb
    CANSTMOB = 0;                   // Clear all the MOb
   }

    CANIE2 = 1;       //Enable interrupt on Mob 0

// Do not give any CAN MOb commands until after the (1 << ENASTB) below.
//  CANPAGE = (0 << MOBNB0);  // Set the MOb page
//  CANSTMOB = 0;             // Clear all the MOb
//
//  CANIDM1 = 0;              //get all messages
//      CANIDM2 = 0;              //1 = check bit
//      CANIDM3 = 0;              //0 = ignore bit
//      CANIDM4 = (1<<IDEMSK);
//  CANCDMOB = (1<<CONMOB1) | (1<<IDE);   // Set MOb to extended format and as reception mob.

    CANBT1 = 0x02;              // Timing - Baud Rate 
    CANBT2 = 0x0C;              // Timing - Re-
    CANBT3 = 0x1B;              // Timing - Phase Segment 2, Phase Segment 1 and Sample Point.  PS2=001, PS1=101

    // This is the minimum Rx/Tx interrupt enable. It does not include MOb errors, General errors,
    // the BXOK, BOFFI or the OVR IT interrupt.
//  CANGIE = (1 << ENIT) | (1 << ENRX) | (1 << ENTX);
    CANGIE = (1 << ENIT) | (1 << ENRX);

    CANGCON = (1 << ENASTB);    // Enable the CAN.

    CANPAGE = (0 << MOBNB0);  // Set the MOb page
//  CANSTMOB = 0;             // Clear all the MOb -- Already just done above.

    CANIDT4 = 0;              // RB1TAG and RB0TAG must be zero values.
        // All other CANIDT bits do not matter because CANIDM.IDEMSK=1 (29 bit ID),
        // CANIDM.RTRMSK=0 (data frame or remote frame) so CANIDT4.RTRTAG is do not care,
        // all CANIDM.IDMSKn (n is 0 to 29) bits are zero so CANIDT.IDTn (0 to 29) bits are do not care.
//  CANIDM1 = 0;              //get all messages
//      CANIDM2 = 0;              //1 = check bit
//      CANIDM3 = 0;              //0 = ignore bit
//      CANIDM4 = (1<<IDEMSK);
        CANIDM = (1<<IDEMSK);			// Does the same thing.
    CANCDMOB = (1<<CONMOB1) | (1<<IDE);   // Set MOb to extended format and as reception mob.
}



volatile MOb can_msg[RxCanSize];
volatile uint8_t can_tail;
volatile uint8_t can_head;
/*
Looptime approx 36,7uS
*/


char can_tx (MOb msg)
{
unsigned char i;
    uint8_t temp = CANPAGE;     //save CANPAGE

//enable MOb1, auto increment index, start with index = 0
    CANPAGE = (1<<MOBNB0);

//  if((  CANCDMOB & 0b11000000) && ( (CANSTMOB & 0x40) ==0))
    if ((CANEN & (1 << ENMOB1)) != 0)       // Is MOb 1 still busy and in use?
    {
        CANPAGE = temp;     //restore CANPAGE
        return false;
    }

//  msg.id <<= 3;          //write 29 Bit identifier
//  CANIDT4 = (unsigned char) (msg.id&0xF8);
//  CANIDT3 = (unsigned char) (msg.id>>8);
//  CANIDT2 = (unsigned char) (msg.id>>16);
//  CANIDT1 = (unsigned char) (msg.id>>24);
    CANIDT = (msg.id << 3);                     // This leaves RTRTAG, RB1TAG and RB0TAG all zero.
    CANIDM = 0;                                 // Initialize all the reserved bits as per the data sheet.
                                                // CANIDM is not used for Tx, but the data sheet wants it initialized.

    for (i=0; i<8; i++)      //put data in mailbox
        CANMSG = msg.data [i];

    CANSTMOB = 0x00;        // cancel pending operation
    CANCDMOB = (1<<CONMOB0) | (1<<IDE) | (8<<DLC0);               //enable transmission //set IDE bit, length = 8

    CANPAGE = temp;                        //restore CANPAGE

    return true;
}



ISR(CANIT_vect)                  //receive interrupt
{   
    uint8_t temp = CANPAGE;            //save CANPAGE
    unsigned char i;
    uint8_t head;
    MOb msg;

    CANPAGE = (0 << MOBNB0);                        //select MOb0
//  msg.len = CANCDMOB & 0x08;
    msg.len = CANCDMOB & 0x0F;
    if (msg.len > 8)
        msg.len = 8;
    if ((CANIDT4 & (1 << RTRTAG)) != 0)
        msg.len = 0;                                // Remote frames to not have any CANMSG data bytes.
       
//  for (i=0; i<8; i++)      //get data
    for (i=0; i < msg.len; i++)      //get data
        msg.data [i] = CANMSG;

//  msg.id = 0;
//  msg.id |= ((unsigned long) CANIDT1<<24);   //get identifier
//  msg.id |= ((unsigned long) CANIDT2<<16);
//  msg.id |= ((unsigned long) CANIDT3<<8);
//  msg.id |= (CANIDT4 & 0xF8);
//  msg.id >>= 3;]
    msg.id = (CANIDT >> 3);

    head = ((can_head + 1) & RxCanMask);
    can_msg[can_head] = msg;

    if ( head != can_tail)
        can_head = head;

    CANSTMOB = 0;               //clear interrupt flag
    CANCDMOB = (1<<CONMOB1) | (1<<IDE);      //reconfig mailbox

    CANPAGE = temp;                        //restore CANPAGE
//  CANSTMOB = 0;               //clear interrupt flag
// After restoring CANPAGE you do not even know what CANPAGE is pointing at. The above CANSTMOB=0 will
// randomly clear some MOb CANSTMOB register. This is a bug that needs to be removed.
}