struct CAN_MSG {
	uint32_t id;
	uint8_t eff;	// 1 für EFF message
	uint8_t rtr;	// 1 für remote transmission request
	uint8_t length;
	uint8_t data [8];
};

struct CAN_MSG sja1000_read_msg(void) {

	uint8_t start_address = 16;
	uint8_t buffer;
	
	struct CAN_MSG msg;
	
	buffer = sja1000_low_level_read(start_address++);
	if (buffer & (1<<7)) msg.eff = 1; else msg.eff = 0;
	if (buffer & (1<<6)) msg.rtr = 1; else msg.rtr = 0;
	
	msg.length = buffer & 0x0F;
	
	if (msg.eff) {
		msg.id = ((uint32_t)(sja1000_low_level_read(start_address++)))<<24;
		msg.id |= ((uint32_t)(sja1000_low_level_read(start_address++)))<<16;
		msg.id |= ((uint32_t)(sja1000_low_level_read(start_address++)))<<8;
		msg.id |= ((uint32_t)(sja1000_low_level_read(start_address++)));
		msg.id = msg.id>>3;
	} else {
		msg.id = ((uint32_t)(sja1000_low_level_read(start_address++)))<<8;
		msg.id |= ((uint32_t)(sja1000_low_level_read(start_address++)));
		msg.id = msg.id>>5;
	}
	for (uint8_t i=0; i<msg.length; i++) msg.data[i] = sja1000_low_level_read(start_address++);
	sja1000_low_level_write(1, (1<<2));	// release receive buffer;
	return msg;	
}

void sja1000_write_msg(struct CAN_MSG * msg) {

	uint8_t start_address = 16;
	
	sja1000_low_level_write(start_address++, (msg->eff<<7) | (msg->rtr<<6) | (msg->length));
	if (msg->eff) {		// Ist es ne EFF Message?
		sja1000_low_level_write(start_address++, (uint8_t)((msg->id<<3)>>24));
		sja1000_low_level_write(start_address++, (uint8_t)((msg->id<<3)>>16));
		sja1000_low_level_write(start_address++, (uint8_t)((msg->id<<3)>>8));
		sja1000_low_level_write(start_address++, (uint8_t)((msg->id<<3)|(msg->rtr<<2)));
	} else {
		sja1000_low_level_write(start_address++, (uint8_t)((msg->id<<5)>>8));
		sja1000_low_level_write(start_address++, ((uint8_t)(msg->id<<5))|(msg->rtr<<4));
	}
	for (uint8_t i=0; i<msg->length; i++) sja1000_low_level_write(start_address++, msg->data[i]);
	sja1000_low_level_write(1, 1<<0);	// sende die Nachricht auf den Bus; <<4 für self reception request
}