l1.c

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    /* some error in UART */
    if( *c < 0 ) {
	*result = BRL1_LINK;
	return 0;
    }

    /* everything's fine */
    *result = BRL1_VALID;
    return 1;
}


/*
 * brl1_receive
 *
 * This function reads a Bedrock-L1 protocol packet into the l1sc_t
 * response buffer.
 *
 * The operation of this function can be expressed as a finite state
 * machine:
 *

START STATE			INPUT		TRANSITION
==========================================================
BRL1_IDLE (reset or error)	flag		BRL1_FLAG
				other		BRL1_IDLE@

BRL1_FLAG (saw a flag (0x7e))	flag		BRL1_FLAG
				escape		BRL1_IDLE@
				header byte	BRL1_HDR
				other		BRL1_IDLE@

BRL1_HDR (saw a type/subch byte)(see below)	BRL1_BODY
						BRL1_HDR

BRL1_BODY (reading packet body)	flag		BRL1_FLAG
				escape		BRL1_ESC
				other		BRL1_BODY

BRL1_ESC (saw an escape (0x7d))	flag		BRL1_FLAG@
				escape		BRL1_IDLE@
				other		BRL1_BODY
==========================================================

"@" denotes an error transition.

 * The BRL1_HDR state is a transient state which doesn't read input,
 * but just provides a way in to code which decides to whom an
 * incoming packet should be directed.
 *
 * brl1_receive can be used to poll for input from the L1, or as 
 * an interrupt service routine.  It reads as much data as is
 * ready from the junk bus UART and places into the appropriate
 * input queues according to subchannel.  The header byte is
 * stripped from console-type data, but is retained for message-
 * type data (L1 responses).  A length byte will also be
 * prepended to message-type packets.
 *
 * This routine is non-blocking; if the caller needs to block
 * for input, it must call brl1_receive in a loop.
 *
 * brl1_receive returns when there is no more input, the queue
 * for the current incoming message is full, or there is an
 * error (parity error, bad header, bad CRC, etc.).
 */

#define STATE_SET(l,s)	((l)->brl1_state = (s))
#define STATE_GET(l)	((l)->brl1_state)

#define LAST_HDR_SET(l,h)	((l)->brl1_last_hdr = (h))
#define LAST_HDR_GET(l)		((l)->brl1_last_hdr)

#define SEQSTAMP_INCR(l)
#define SEQSTAMP_GET(l)

#define VALID_HDR(c)				\
    ( SUBCH((c)) <= SC_CONS_SYSTEM		\
	? PKT_TYPE((c)) == BRL1_REQUEST		\
	: ( PKT_TYPE((c)) == BRL1_RESPONSE ||	\
	    PKT_TYPE((c)) == BRL1_EVENT ) )

#define IS_TTY_PKT(l) \
         ( SUBCH(LAST_HDR_GET(l)) <= SC_CONS_SYSTEM ? 1 : 0 )


int
brl1_receive( l1sc_t *sc )
{
    int result;		/* value to be returned by brl1_receive */
    int c;		/* most-recently-read character	     	*/
    int done;		/* set done to break out of recv loop	*/
    sc_cq_t *q;		/* pointer to queue we're working with	*/

    result = BRL1_NO_MESSAGE;

#ifdef FORCE_CONSOLE_NASID
    sc->nasid = 0;
#endif
    if ( sc->uart == BRL1_LOCALUART )
	lock_console(sc->nasid);

    done = 0;
    while( !done )
    {
	switch( STATE_GET(sc) )
	{

	  case BRL1_IDLE:
	    /* Initial or error state.  Waiting for a flag character
             * to resynchronize with the L1.
             */

	    if( !read_uart( sc, &c, &result ) ) {

		/* error reading uart */
		done = 1;
		continue;
	    }
	    
	    if( c == BRL1_FLAG_CH ) {
		/* saw a flag character */
		STATE_SET( sc, BRL1_FLAG );
		continue;
	    }
	    break;
	    
	  case BRL1_FLAG:
	    /* One or more flag characters have been read; look for
	     * the beginning of a packet (header byte).
	     */
	    
	    if( !read_uart( sc, &c, &result ) ) {

		/* error reading uart */
		if( c != UART_NO_CHAR )
		    STATE_SET( sc, BRL1_IDLE );

		done = 1;
		continue;
	    }
	    
	    if( c == BRL1_FLAG_CH ) {
		/* multiple flags are OK */
		continue;
	    }

	    if( !VALID_HDR( c ) ) {
		/* if c isn't a flag it should have been
		 * a valid header, so we have an error
		 */
		result = BRL1_PROTOCOL;
		STATE_SET( sc, BRL1_IDLE );
		done = 1;
		continue;
	    }

	    /* we have a valid header byte */
	    LAST_HDR_SET( sc, c );
	    STATE_SET( sc, BRL1_HDR );

	    break; 

	  case BRL1_HDR:
	    /* A header byte has been read. Do some bookkeeping. */
	    q = sc->subch[ SUBCH( LAST_HDR_GET(sc) ) ].iqp;
	    ASSERT(q);
	    
	    if( !IS_TTY_PKT(sc) ) {
		/* if this is an event or command response rather
		 * than console I/O, we need to reserve a couple
		 * of extra spaces in the queue for the header
		 * byte and a length byte; if we can't, stay in
		 * the BRL1_HDR state.
		 */
		if( cq_room( q ) < 2 ) {
		    result = BRL1_FULL_Q;
		    done = 1;
		    continue;
		}
		cq_tent_add( q, 0 );			/* reserve length byte */
		cq_tent_add( q, LAST_HDR_GET( sc ) );	/* record header byte  */
	    }
	    STATE_SET( sc, BRL1_BODY );

	    break;

	  case BRL1_BODY:
	    /* A header byte has been read.  We are now attempting
	     * to receive the packet body.
	     */

	    q = sc->subch[ SUBCH( LAST_HDR_GET(sc) ) ].iqp;
	    ASSERT(q);

	    /* if the queue we want to write into is full, don't read from
	     * the uart (this provides backpressure to the L1 side)
	     */
	    if( cq_tent_full( q ) ) {
		result = BRL1_FULL_Q;
		done = 1;
		continue;
	    }
	    
	    if( !read_uart( sc, &c, &result ) ) {

		/* error reading uart */
		if( c != UART_NO_CHAR )
		    STATE_SET( sc, BRL1_IDLE );
		done = 1;
		continue;
	    }

	    if( c == BRL1_ESC_CH ) {
		/* prepare to unescape the next character */
		STATE_SET( sc, BRL1_ESC );
		continue;
	    }
	    
	    if( c == BRL1_FLAG_CH ) {
		/* flag signifies the end of a packet */

		unsigned short crc;	/* holds the crc as we calculate it */
		int i;			/* index variable */
		brl1_sch_t *subch;      /* subchannel for received packet */
		brl1_notif_t callup;	/* "data ready" callup */

		/* whatever else may happen, we've seen a flag and we're
		 * starting a new packet
		 */
		STATE_SET( sc, BRL1_FLAG );
		SEQSTAMP_INCR(sc); /* bump the packet sequence counter */
		
		/* if the packet body has less than 2 characters,
		 * it can't be a well-formed packet.  Discard it.
		 */
		if( cq_tent_len( q ) < /* 2 + possible length byte */
		    (2 + (IS_TTY_PKT(sc) ? 0 : 1)) )
		{
		    result = BRL1_PROTOCOL;
		    cq_discard_tent( q );
		    STATE_SET( sc, BRL1_FLAG );
		    done = 1;
		    continue;
		}
		
		/* check CRC */

		/* accumulate CRC, starting with the header byte and
		 * ending with the transmitted CRC.  This should
		 * result in a known good value.
		 */
		crc = crc16_calc( INIT_CRC, LAST_HDR_GET(sc) );
		for( i = (q->ipos + (IS_TTY_PKT(sc) ? 0 : 2)) % BRL1_QSIZE;
		     i != q->tent_next;
		     i = (i + 1) % BRL1_QSIZE )
		{
		    crc = crc16_calc( crc, q->buf[i] );
		}

		/* verify the caclulated crc against the "good" crc value;
		 * if we fail, discard the bad packet and return an error.
		 */
		if( crc != (unsigned short)GOOD_CRC ) {
		    result = BRL1_CRC;
		    cq_discard_tent( q );
		    STATE_SET( sc, BRL1_FLAG );
		    done = 1;
		    continue;
		}
		
		/* so the crc check was ok.  Now we discard the CRC
		 * from the end of the received bytes.
		 */
		q->tent_next += (BRL1_QSIZE - 2);
		q->tent_next %= BRL1_QSIZE;

		/* get the subchannel and lock it */
		subch = &(sc->subch[SUBCH( LAST_HDR_GET(sc) )]);
		SUBCH_DATA_LOCK( subch );
		
		/* if this isn't a console packet, we need to record
		 * a length byte
		 */
		if( !IS_TTY_PKT(sc) ) {
		    q->buf[q->ipos] = cq_tent_len( q ) - 1;
		}
		
		/* record packet for posterity */
		cq_commit_tent( q );
		result = BRL1_VALID;

		/* notify subchannel owner that there's something
		 * on the queue for them
		 */
		atomic_inc(&(subch->packet_arrived));
		callup = subch->rx_notify;
		SUBCH_DATA_UNLOCK( subch );

		if( callup ) {
		    if ( sc->uart == BRL1_LOCALUART )
			unlock_console(sc->nasid);
		    (*callup)( sc, SUBCH(LAST_HDR_GET(sc)) );
		    if ( sc->uart == BRL1_LOCALUART )
			lock_console(sc->nasid);
		}
		continue;	/* go back for more! */
	    }
	    
	    /* none of the special cases applied; we've got a normal
	     * body character
	     */
	    cq_tent_add( q, c );

	    break;

	  case BRL1_ESC:
	    /* saw an escape character.  The next character will need
	     * to be unescaped.
	     */

	    q = sc->subch[ SUBCH( LAST_HDR_GET(sc) ) ].iqp;
	    ASSERT(q);

	    /* if the queue we want to write into is full, don't read from
	     * the uart (this provides backpressure to the L1 side)
	     */
	    if( cq_tent_full( q ) ) {
		result = BRL1_FULL_Q;
		done = 1;
		continue;
	    }
	    
	    if( !read_uart( sc, &c, &result ) ) {

		/* error reading uart */
		if( c != UART_NO_CHAR ) {
		    cq_discard_tent( q );
		    STATE_SET( sc, BRL1_IDLE );
		}
		done = 1;
		continue;
	    }
	    
	    if( c == BRL1_FLAG_CH ) {
		/* flag after escape is an error */
		STATE_SET( sc, BRL1_FLAG );
		cq_discard_tent( q );
		result = BRL1_PROTOCOL;
		done = 1;
		continue;
	    }

	    if( c == BRL1_ESC_CH ) {
		/* two consecutive escapes is an error */
		STATE_SET( sc, BRL1_IDLE );
		cq_discard_tent( q );
		result = BRL1_PROTOCOL;
		done = 1;
		continue;
	    }
	    
	    /* otherwise, we've got a character that needs
	     * to be unescaped
	     */
	    cq_tent_add( q, (c ^ BRL1_XOR_CH) );
	    STATE_SET( sc, BRL1_BODY );

	    break;

	} /* end of switch( STATE_GET(sc) ) */
    } /* end of while(!done) */
    
    if ( sc->uart == BRL1_LOCALUART )
	unlock_console(sc->nasid);

    return result;
}	    


/* brl1_init initializes the Bedrock/L1 protocol layer.  This includes
 * zeroing out the send and receive state information.
 */

void
brl1_init( l1sc_t *sc, nasid_t nasid, net_vec_t uart )
{
    int i;
    brl1_sch_t *subch;

    bzero( sc, sizeof( *sc ) );
#ifdef FORCE_CONSOLE_NASID
    nasid = (nasid_t)0;
#endif
    sc->nasid = nasid;
    sc->uart = uart;
    sc->getc_f = (uart == BRL1_LOCALUART ? uart_getc : rtr_uart_getc);
    sc->putc_f = (uart == BRL1_LOCALUART ? uart_putc : rtr_uart_putc);
    sc->sol = 1;
    subch = sc->subch;

    /* initialize L1 subchannels
     */

    /* assign processor TTY channels */
    for( i = 0; i < CPUS_PER_NODE; i++, subch++ ) {
	subch->use = BRL1_SUBCH_RSVD;
	subch->packet_arrived = ATOMIC_INIT(0);
	spin_lock_init( &(subch->data_lock) );
	sv_init( &(subch->arrive_sv), &(subch->data_lock), SV_MON_SPIN | SV_ORDER_FIFO /* | SV_INTS */ );
	subch->tx_notify = NULL;
	/* (for now, drop elscuart packets in the kernel) */
	subch->rx_notify = brl1_discard_packet;
	subch->iqp = &sc->garbage_q;
    }

    /* assign system TTY channel (first free subchannel after each
     * processor's individual TTY channel has been assigned)
     */
    subch->use = BRL1_SUBCH_RSVD;
    subch->packet_arrived = ATOMIC_INIT(0);
    spin_lock_init( &(subch->data_lock) );
    sv_init( &(subch->arrive_sv), &subch->data_lock, SV_MON_SPIN | SV_ORDER_FIFO /* | SV_INTS */ );
    subch->tx_notify = NULL;
    if( sc->uart == BRL1_LOCALUART ) {
	subch->iqp = kmem_zalloc_node( sizeof(sc_cq_t), KM_NOSLEEP,
				       NASID_TO_COMPACT_NODEID(nasid) );
	ASSERT( subch->iqp );
	cq_init( subch->iqp );
	subch->rx_notify = NULL;
    }
    else {
	/* we shouldn't be getting console input from remote UARTs */
	subch->iqp = &sc->garbage_q;
	subch->rx_notify = brl1_discard_packet;
    }
    subch++; i++;

    /* "reserved" subchannels (0x05-0x0F); for now, throw away
     * incoming packets
     */
    for( ; i < 0x10; i++, subch++ ) {
	subch->use = BRL1_SUBCH_FREE;
	subch->packet_arrived = ATOMIC_INIT(0);
	subch->tx_notify = NULL;
	subch->rx_notify = brl1_discard_packet;
	subch->iqp = &sc->garbage_q;
    }

    /* remaining subchannels are free */
    for( ; i < BRL1_NUM_SUBCHANS; i++, subch++ ) {
	subch->use = BRL1_SUBCH_FREE;
	subch->packet_arrived = ATOMIC_INIT(0);
	subch->tx_notify = NULL;
	subch->rx_notify = brl1_discard_packet;
	subch->iqp = &sc->garbage_q;
    }

    /* initialize synchronization structures
     */
    spin_lock_init( &(sc->subch_lock) );

    if( sc->uart == BRL1_LOCALUART ) {
	uart_init( sc, UART_BAUD_RATE );
    }
    else {
	rtr_uart_init( sc, UART_BAUD_RATE );
    }

    /* Set up remaining fields using L1 command functions-- elsc_module_get
     * to read the module id, elsc_debug_get to see whether or not we're
     * in verbose mode.
     */
    {
	extern int elsc_module_get(l1sc_t *);

	sc->modid = elsc_module_get( sc );
	sc->modid = (sc->modid < 0 ? INVALID_MODULE : sc->modid);
	sc->verbose = 1;
    }
}


/* These are functions to use from serial_in/out when in protocol
 * mode to send and receive uart control regs. These are external
 * interfaces into the protocol driver.
 */
void
l1_control_out(int offset, int value)
{
	nasid_t nasid = 0; //(get_elsc())->nasid;
	WRITE_L1_UART_REG(nasid, offset, value);