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Darwin 0.2 Driver Kit

			Ethernet error handling
			
Transmit errors

* All errors: we don't know which buffer caused error, due to the design 
  of the TE. In all cases we have to dequeue everything and throw them 
  all away.
  
* channel errorInterrupt, busError
  -- action:
  	reset, dequeue and discard all frames
	 
  << the rest of these are in etxAddlInt_t >>
  
* Late collision
  -- Disables channel
  -- action:
  	reset, dequeue and discard all frames
  
* underrun
  -- Disables channel
  -- action:
  	reset, dequeue and discard all frames
	
* No Heart beat
  -- Only useful for TPE; mask off for thin wire
  -- Channel not disabled
  -- action:
    	reset, dequeue and discard all frames;
        enJam();
	
* > 15 retries
  -- Disables channel
  -- action:
    	reset, dequeue and discard all frames;
        enJam();
		
Receive errors

* descriptor chan_status errors
  * short packet - should never happen
  * alignment error
  * CRC error 
  * collided packet
  -- Action:
  	drop packet on floor.
	
* channel errorInterrupt, busError
  -- Disables channel (maybe...)
  -- action:
  	dmaAbort (to be sure);
  	dequeue completed frames and restart;
	
* overrun
  -- Disables channel
  -- action:
  	dequeue completed frames and restart;
	
* CRC error - mask this interrupt; detected in descriptor chan_status

* Alignment error - mask this interrupt; detected in descriptor user status

Net Jammed errors

* detected:
  -- > 15 retries, s/w retry count exceeded
  -- No heart beat, s/w retry count exceeded
  -- timeout on TX interrupt 
  
* Action:
  
m68k en_jam() {
  	if TPE selected {
		if link integrity OK
			return good;
		else {
			select Thin wire;
			enable LoopBack (??);
			return error;
		}
			
	}
	else (thin wire selected) {	
		if link integrity of TPE OK {
			select TPE;
			Enable loopback (??);
			return GOOD;
		}
		else {
			log "Net Jammed" message if we haven't already done so;
			set ENF_JAMMED flag;
			if_down();
			timeout(antijam); // clears ENF_JAMMED flag after 10 
					  //   seconds
			return error;
		}
	}
}
  
m88k enJam() {

   	if (++retry_count < max) 
		return good;

	remember current I/F mode (TPE or thin);
	select TPE;
	wait some h/w delay for Link Integrity to settle down;
	if link integrity good {
		return good;
	}
	else if (mode was TPE on entry) {
		select Thin wire;
		return good;
	}
	
	/* 
	 * Net down.
	 */
	dequeue and free all frames;
	set net_down flag; set timeout to clear it in 10 seconds;
	if_down();
	return bad;
}

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