dev/aic7xxx/aic7xxx.seq

/*
 * Adaptec 274x/284x/294x device driver firmware for Linux and FreeBSD.
 *
 * Copyright (c) 1994-2000 Justin Gibbs.
 * 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,
 *    without modification.
 * 2. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * Alternatively, this software may be distributed under the terms of the
 * the GNU Public License ("GPL").
 *
 * 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 AUTHOR 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.
 *
 * $FreeBSD$
 */

#include <dev/aic7xxx/aic7xxx.reg>
#include <cam/scsi/scsi_message.h>

/*
 * A few words on the waiting SCB list:
 * After starting the selection hardware, we check for reconnecting targets
 * as well as for our selection to complete just in case the reselection wins
 * bus arbitration.  The problem with this is that we must keep track of the
 * SCB that we've already pulled from the QINFIFO and started the selection
 * on just in case the reselection wins so that we can retry the selection at
 * a later time.  This problem cannot be resolved by holding a single entry
 * in scratch ram since a reconnecting target can request sense and this will
 * create yet another SCB waiting for selection.  The solution used here is to
 * use byte 27 of the SCB as a psuedo-next pointer and to thread a list
 * of SCBs that are awaiting selection.  Since 0-0xfe are valid SCB indexes,
 * SCB_LIST_NULL is 0xff which is out of range.  An entry is also added to
 * this list everytime a request sense occurs or after completing a non-tagged
 * command for which a second SCB has been queued.  The sequencer will
 * automatically consume the entries.
 */

reset:
	clr	SCSISIGO;		/* De-assert BSY */
	mvi	MSG_OUT, MSG_NOOP;	/* No message to send */
	and	SXFRCTL1, ~BITBUCKET;
	/* Always allow reselection */
	and	SCSISEQ, ENSELI|ENRSELI|ENAUTOATNP, SCSISEQ_TEMPLATE;
	if ((ahc->features & AHC_CMD_CHAN) != 0) {
		/* Ensure that no DMA operations are in progress */
		clr	CCSGCTL;
		clr	CCSCBCTL;
	}

poll_for_work:
	call	clear_target_state;
	and	SXFRCTL0, ~SPIOEN;
	if ((ahc->features & AHC_QUEUE_REGS) == 0) {
		mov	A, QINPOS;
	}
poll_for_work_loop:
	if ((ahc->features & AHC_QUEUE_REGS) == 0) {
		and	SEQCTL, ~PAUSEDIS;
	}
	test	SSTAT0, SELDO|SELDI	jnz selection;
	test	SCSISEQ, ENSELO	jnz poll_for_work;
	if ((ahc->features & AHC_TWIN) != 0) {
		/*
		 * Twin channel devices cannot handle things like SELTO
		 * interrupts on the "background" channel.  So, if we
		 * are selecting, keep polling the current channel util
		 * either a selection or reselection occurs.
		 */
		xor	SBLKCTL,SELBUSB;	/* Toggle to the other bus */
		test	SSTAT0, SELDO|SELDI	jnz selection;
		test	SCSISEQ, ENSELO	jnz poll_for_work;
		xor	SBLKCTL,SELBUSB;	/* Toggle back */
	}
	cmp	WAITING_SCBH,SCB_LIST_NULL jne start_waiting;
test_queue:
	/* Has the driver posted any work for us? */
	if ((ahc->features & AHC_QUEUE_REGS) != 0) {
		test	QOFF_CTLSTA, SCB_AVAIL jz poll_for_work_loop;
		mov	NONE, SNSCB_QOFF;
		inc	QINPOS;
	} else {
		or	SEQCTL, PAUSEDIS;
		cmp	KERNEL_QINPOS, A je poll_for_work_loop;
		inc	QINPOS;
		and	SEQCTL, ~PAUSEDIS;
	}

/*
 * We have at least one queued SCB now and we don't have any
 * SCBs in the list of SCBs awaiting selection.  If we have
 * any SCBs available for use, pull the tag from the QINFIFO
 * and get to work on it.
 */
	if ((ahc->flags & AHC_PAGESCBS) != 0) {
		mov	ALLZEROS	call	get_free_or_disc_scb;
	}

dequeue_scb:
	add	A, -1, QINPOS;
	mvi	QINFIFO_OFFSET call fetch_byte;

	if ((ahc->flags & AHC_PAGESCBS) == 0) {
		/* In the non-paging case, the SCBID == hardware SCB index */
		mov	SCBPTR, RETURN_2;
	}
dma_queued_scb:
/*
 * DMA the SCB from host ram into the current SCB location.
 */
	mvi	DMAPARAMS, HDMAEN|DIRECTION|FIFORESET;
	mov	RETURN_2	 call dma_scb;

/*
 * Preset the residual fields in case we never go through a data phase.
 * This isn't done by the host so we can avoid a DMA to clear these
 * fields for the normal case of I/O that completes without underrun
 * or overrun conditions.
 */
	if ((ahc->features & AHC_CMD_CHAN) != 0) {
		bmov	SCB_RESID_DCNT, SCB_DATACNT, 3;
	} else {
		mov	SCB_RESID_DCNT[0],SCB_DATACNT[0];
		mov	SCB_RESID_DCNT[1],SCB_DATACNT[1];
		mov	SCB_RESID_DCNT[2],SCB_DATACNT[2];
	}
	mov	SCB_RESID_SGCNT, SCB_SGCOUNT;

start_scb:
	/*
	 * Place us on the waiting list in case our selection
	 * doesn't win during bus arbitration.
	 */
	mov	SCB_NEXT,WAITING_SCBH;
	mov	WAITING_SCBH, SCBPTR;
start_waiting:
	/*
	 * Pull the first entry off of the waiting SCB list.
	 */
	mov	SCBPTR, WAITING_SCBH;
	call	start_selection;
	jmp	poll_for_work;

start_selection:
	if ((ahc->features & AHC_TWIN) != 0) {
		and	SINDEX,~SELBUSB,SBLKCTL;/* Clear channel select bit */
		and	A,SELBUSB,SCB_TCL;	/* Get new channel bit */
		or	SINDEX,A;
		mov	SBLKCTL,SINDEX;		/* select channel */
	}
initialize_scsiid:
	mov	SINDEX, SCSISEQ_TEMPLATE;
	if ((ahc->flags & AHC_TARGETMODE) != 0) {
		test	SCB_CONTROL, TARGET_SCB jz . + 4;
		if ((ahc->features & AHC_ULTRA2) != 0) {
			mov	SCSIID_ULTRA2, SCB_CMDPTR[2];
		} else {
			mov	SCSIID, SCB_CMDPTR[2];
		}
		or	SINDEX, TEMODE;
		jmp	initialize_scsiid_fini;
	}
	if ((ahc->features & AHC_ULTRA2) != 0) {
		and	A, TID, SCB_TCL;	/* Get target ID */
		and	SCSIID_ULTRA2, OID;	/* Clear old target */
		or	SCSIID_ULTRA2, A;
	} else {
		and	A, TID, SCB_TCL;	/* Get target ID */
		and	SCSIID, OID;		/* Clear old target */
		or	SCSIID, A;
	}
initialize_scsiid_fini:
	mov	SCSISEQ, SINDEX ret;

/*
 * Initialize transfer settings and clear the SCSI channel.
 * SINDEX should contain any additional bit's the client wants
 * set in SXFRCTL0.  We also assume that the current SCB is
 * a valid SCB for the target we wish to talk to.
 */
initialize_channel:
	or	SXFRCTL0, CLRSTCNT|CLRCHN, SINDEX;
set_transfer_settings:
	if ((ahc->features & AHC_ULTRA) != 0) {
		test	SCB_CONTROL, ULTRAENB jz . + 2;
		or	SXFRCTL0, FAST20;
	}
/*
 * Initialize SCSIRATE with the appropriate value for this target.
 */
	if ((ahc->features & AHC_ULTRA2) != 0) {
		bmov	SCSIRATE, SCB_SCSIRATE, 2 ret;
	} else {
		mov	SCSIRATE, SCB_SCSIRATE ret;
	}

selection:
	test	SSTAT0,SELDO	jnz select_out;
	mvi	CLRSINT0, CLRSELDI;
select_in:
	if ((ahc->flags & AHC_TARGETMODE) != 0) {
		if ((ahc->flags & AHC_INITIATORMODE) != 0) {
			test	SSTAT0, TARGET	jz initiator_reselect;
		}

		/*
		 * We've just been selected.  Assert BSY and
		 * setup the phase for receiving messages
		 * from the target.
		 */
		mvi	SCSISIGO, P_MESGOUT|BSYO;
		mvi	CLRSINT1, CLRBUSFREE;

		/*
		 * Setup the DMA for sending the identify and
		 * command information.
		 */
		or	SEQ_FLAGS, CMDPHASE_PENDING;

		mov     A, TQINPOS;
		if ((ahc->features & AHC_CMD_CHAN) != 0) {
			mvi	DINDEX, CCHADDR;
			mvi	TMODE_CMDADDR call set_32byte_addr;
			mvi	CCSCBCTL, CCSCBRESET;
		} else {
			mvi	DINDEX, HADDR;
			mvi	TMODE_CMDADDR call set_32byte_addr;
			mvi	DFCNTRL, FIFORESET;
		}

		/* Initiator that selected us */
		and	SAVED_TCL, SELID_MASK, SELID;
		if ((ahc->features & AHC_CMD_CHAN) != 0) {
			mov	CCSCBRAM, SAVED_TCL;
		} else {
			mov	DFDAT, SAVED_TCL;
		}

		/* The Target ID we were selected at */
		if ((ahc->features & AHC_CMD_CHAN) != 0) {
			if ((ahc->features & AHC_MULTI_TID) != 0) {
				and	CCSCBRAM, OID, TARGIDIN;
			} else if ((ahc->features & AHC_ULTRA2) != 0) {
				and	CCSCBRAM, OID, SCSIID_ULTRA2;
			} else {
				and	CCSCBRAM, OID, SCSIID;
			}
		} else {
			if ((ahc->features & AHC_MULTI_TID) != 0) {
				and	DFDAT, OID, TARGIDIN;
			} else if ((ahc->features & AHC_ULTRA2) != 0) {
				and	DFDAT, OID, SCSIID_ULTRA2;
			} else {
				and	DFDAT, OID, SCSIID;
			}
		}

		/* No tag yet */
		mvi	INITIATOR_TAG, SCB_LIST_NULL;

		/*
		 * If ATN isn't asserted, the target isn't interested
		 * in talking to us.  Go directly to bus free.
		 */
		test	SCSISIGI, ATNI	jz	target_busfree;

		/*
		 * Watch ATN closely now as we pull in messages from the
		 * initiator.  We follow the guidlines from section 6.5
		 * of the SCSI-2 spec for what messages are allowed when.
		 */
		call	target_inb;

		/*
		 * Our first message must be one of IDENTIFY, ABORT, or
		 * BUS_DEVICE_RESET.
		 */
		/* XXX May need to be more lax here for older initiators... */
		test	DINDEX, MSG_IDENTIFYFLAG jz host_target_message_loop;
		/* Store for host */
		if ((ahc->features & AHC_CMD_CHAN) != 0) {
			mov	CCSCBRAM, DINDEX;
		} else {
			mov	DFDAT, DINDEX;
		}

		/* Remember for disconnection decision */
		test	DINDEX, MSG_IDENTIFY_DISCFLAG jnz . + 2;
		/* XXX Honor per target settings too */
		or	SEQ_FLAGS, NO_DISCONNECT;

		test	SCSISIGI, ATNI	jz	ident_messages_done;
		call	target_inb;
		/*
		 * If this is a tagged request, the tagged message must
		 * immediately follow the identify.  We test for a valid
		 * tag message by seeing if it is >= MSG_SIMPLE_Q_TAG and
		 * < MSG_IGN_WIDE_RESIDUE.
		 */
		add	A, -MSG_SIMPLE_Q_TAG, DINDEX;
		jnc	ident_messages_done;
		add	A, -MSG_IGN_WIDE_RESIDUE, DINDEX;
		jc	ident_messages_done;
		/* Store for host */
		if ((ahc->features & AHC_CMD_CHAN) != 0) {
			mov	CCSCBRAM, DINDEX;
		} else {
			mov	DFDAT, DINDEX;
		}

		/*
		 * If the initiator doesn't feel like providing a tag number,
		 * we've got a failed selection and must transition to bus
		 * free.
		 */
		test	SCSISIGI, ATNI	jz	target_busfree;

		/*
		 * Store the tag for the host.
		 */
		call	target_inb;
		if ((ahc->features & AHC_CMD_CHAN) != 0) {
			mov	CCSCBRAM, DINDEX;
		} else {
			mov	DFDAT, DINDEX;
		}
		mov	INITIATOR_TAG, DINDEX;
		jmp	ident_messages_done;

		/*
		 * Pushed message loop to allow the kernel to
		 * run it's own target mode message state engine.
		 */
host_target_message_loop:
		mvi	INTSTAT, HOST_MSG_LOOP;
		nop;
		cmp	RETURN_1, EXIT_MSG_LOOP	je target_ITloop;
		test	SSTAT0, SPIORDY jz .;
		jmp	host_target_message_loop;

ident_messages_done:
		/* If ring buffer is full, return busy or queue full */
		mov	A, KERNEL_TQINPOS;
		cmp	TQINPOS, A jne tqinfifo_has_space;
		mvi	P_STATUS|BSYO call change_phase;
		cmp	INITIATOR_TAG, SCB_LIST_NULL je . + 3;
		mvi	STATUS_QUEUE_FULL call target_outb;
		jmp	target_busfree_wait;
		mvi	STATUS_BUSY call target_outb;
		jmp	target_busfree_wait;
tqinfifo_has_space:
		/* Terminate the ident list */
		if ((ahc->features & AHC_CMD_CHAN) != 0) {
			mvi	CCSCBRAM, SCB_LIST_NULL;
		} else {
			mvi	DFDAT, SCB_LIST_NULL;
		}
		or	SEQ_FLAGS, TARG_CMD_PENDING|IDENTIFY_SEEN;
		test	SCSISIGI, ATNI	jnz target_mesgout_pending_msg;
		jmp	target_ITloop;

/*
 * We carefully toggle SPIOEN to allow us to return the
 * message byte we receive so it can be checked prior to
 * driving REQ on the bus for the next byte.
 */
target_inb:
		/*
		 * Drive REQ on the bus by enabling SCSI PIO.
		 */
		or	SXFRCTL0, SPIOEN;
		/* Wait for the byte */
		test	SSTAT0, SPIORDY jz .;
		/* Prevent our read from triggering another REQ */
		and	SXFRCTL0, ~SPIOEN;
		/* Save latched contents */
		mov	DINDEX, SCSIDATL ret;
	}

if ((ahc->flags & AHC_INITIATORMODE) != 0) {
/*
 * Reselection has been initiated by a target. Make a note that we've been
 * reselected, but haven't seen an IDENTIFY message from the target yet.
 */
initiator_reselect:
	/* XXX test for and handle ONE BIT condition */
	and	SAVED_TCL, SELID_MASK, SELID;
	if ((ahc->features & AHC_TWIN) != 0) {
		test	SBLKCTL, SELBUSB	jz . + 2;
		or	SAVED_TCL, SELBUSB;
	}
	or	SXFRCTL0, SPIOEN|CLRSTCNT|CLRCHN;
	mvi	CLRSINT1,CLRBUSFREE;
	or	SIMODE1, ENBUSFREE;		/*
						 * We aren't expecting a
						 * bus free, so interrupt
						 * the kernel driver if it
						 * happens.
						 */
	jmp	ITloop;
}

/*
 * After the selection, remove this SCB from the "waiting SCB"
 * list.  This is achieved by simply moving our "next" pointer into
 * WAITING_SCBH.  Our next pointer will be set to null the next time this
 * SCB is used, so don't bother with it now.
 */
select_out:
	/* Turn off the selection hardware */
	and	SCSISEQ, ENSELI|ENRSELI|ENAUTOATNP, SCSISEQ_TEMPLATE;
	mvi	CLRSINT0, CLRSELDO;
	mov	SCBPTR, WAITING_SCBH;
	mov	WAITING_SCBH,SCB_NEXT;
	mov	SAVED_TCL, SCB_TCL;
	if ((ahc->flags & AHC_TARGETMODE) != 0) {
		test	SSTAT0, TARGET	jz initiator_select;

		/*
		 * We've just re-selected an initiator.
		 * Assert BSY and setup the phase for
		 * sending our identify messages.
		 */
		mvi	P_MESGIN|BSYO call change_phase;
		mvi	CLRSINT1,CLRBUSFREE;

		/*
		 * Start out with a simple identify message.
		 */
		and	A, LID, SCB_TCL;
		or	A, MSG_IDENTIFYFLAG call target_outb;

		/*
		 * If we are the result of a tagged command, send
		 * a simple Q tag and the tag id.
		 */
		test	SCB_CONTROL, TAG_ENB	jz . + 3;
		mvi	MSG_SIMPLE_Q_TAG call target_outb;
		mov	SCB_INITIATOR_TAG call target_outb;
		mov	INITIATOR_TAG, SCB_INITIATOR_TAG;
target_synccmd:
		/*
		 * Now determine what phases the host wants us
		 * to go through.
		 */
		mov	SEQ_FLAGS, SCB_TARGET_PHASES;


target_ITloop:
		/*
		 * Start honoring ATN signals now that
		 * we properly identified ourselves.
		 */
		test	SCSISIGI, ATNI			jnz target_mesgout;
		test	SEQ_FLAGS, CMDPHASE_PENDING	jnz target_cmdphase;
		test	SEQ_FLAGS, DPHASE_PENDING	jnz target_dphase;
		test	SEQ_FLAGS, SPHASE_PENDING	jnz target_sphase;

		/*
		 * No more work to do.  Either disconnect or not depending
		 * on the state of NO_DISCONNECT.
		 */
		test	SEQ_FLAGS, NO_DISCONNECT jz target_disconnect;
		if ((ahc->flags & AHC_PAGESCBS) != 0) {
			mov	ALLZEROS	call	get_free_or_disc_scb;
		}
		mov	RETURN_1, ALLZEROS;
		call	complete_target_cmd;
		cmp	RETURN_1, CONT_MSG_LOOP jne .;
		mvi	DMAPARAMS, HDMAEN|DIRECTION|FIFORESET;
		mov	SCB_TAG	 call dma_scb;
		jmp	target_synccmd;

target_mesgout:
		mvi	SCSISIGO, P_MESGOUT|BSYO;
		call	target_inb;
		/* Local Processing goes here... */
target_mesgout_pending_msg:
		jmp	host_target_message_loop;

target_disconnect:
		mvi	P_MESGIN|BSYO call change_phase;
		test	SEQ_FLAGS, DPHASE	jz . + 2;
		mvi	MSG_SAVEDATAPOINTER call target_outb;
		mvi	MSG_DISCONNECT call target_outb;

target_busfree_wait:
		/* Wait for preceeding I/O session to complete. */
		test	SCSISIGI, ACKI jnz .;
target_busfree:
		clr	SCSISIGO;
		mvi	LASTPHASE, P_BUSFREE;
		call	complete_target_cmd;
		jmp	poll_for_work;

target_cmdphase:
		mvi	P_COMMAND|BSYO call change_phase;
		call	target_inb;
		mov	A, DINDEX;
		/* Store for host */
		if ((ahc->features & AHC_CMD_CHAN) != 0) {
			mov	CCSCBRAM, A;
		} else {
			mov	DFDAT, A;
		}

		/*
		 * Determine the number of bytes to read
		 * based on the command group code via table lookup.
		 * We reuse the first 8 bytes of the TARG_SCSIRATE
		 * BIOS array for this table. Count is one less than
		 * the total for the command since we've already fetched
		 * the first byte.
		 */
		shr	A, CMD_GROUP_CODE_SHIFT;
		add	SINDEX, TARG_SCSIRATE, A;
		mov	A, SINDIR;

		test	A, 0xFF jz command_phase_done;
command_loop:
		or	SXFRCTL0, SPIOEN;
		test	SSTAT0, SPIORDY jz .;
		cmp	A, 1 jne . + 2;
		and	SXFRCTL0, ~SPIOEN;	/* Last Byte */
		if ((ahc->features & AHC_CMD_CHAN) != 0) {
			mov	CCSCBRAM, SCSIDATL;
		} else {
			mov	DFDAT, SCSIDATL;
		}
		dec	A;
		test	A, 0xFF jnz command_loop;

command_phase_done:
		and	SEQ_FLAGS, ~CMDPHASE_PENDING;
		jmp	target_ITloop;

target_dphase:
		/*
		 * Data direction flags are from the
		 * perspective of the initiator.
		 */
		test	SCB_TARGET_PHASES[1], TARGET_DATA_IN jz . + 4;
		mvi	LASTPHASE, P_DATAOUT;
		mvi	P_DATAIN|BSYO call change_phase;
		jmp	. + 3;
		mvi	LASTPHASE, P_DATAIN;
		mvi	P_DATAOUT|BSYO call change_phase;
		mov	ALLZEROS call initialize_channel;
		jmp	p_data;

target_sphase:
		mvi	P_STATUS|BSYO call change_phase;
		mvi	LASTPHASE, P_STATUS;
		mov	SCB_TARGET_STATUS call target_outb;
		/* XXX Watch for ATN or parity errors??? */
		mvi	SCSISIGO, P_MESGIN|BSYO;
		/* MSG_CMDCMPLT is 0, but we can't do an immediate of 0 */
		mov	ALLZEROS call target_outb;
		jmp	target_busfree_wait;

complete_target_cmd:
		test	SEQ_FLAGS, TARG_CMD_PENDING	jnz . + 2;
		mov	SCB_TAG jmp complete_post;
		if ((ahc->features & AHC_CMD_CHAN) != 0) {
			/* Set the valid byte */
			mvi	CCSCBADDR, 24;
			mov	CCSCBRAM, ALLONES;
			mvi	CCHCNT, 28;
			or	CCSCBCTL, CCSCBEN|CCSCBRESET;
			test	CCSCBCTL, CCSCBDONE jz .;
			clr	CCSCBCTL;
		} else {
			/* Set the valid byte */
			or	DFCNTRL, FIFORESET;
			mvi	DFWADDR, 3; /* Third 64bit word or byte 24 */
			mov	DFDAT, ALLONES;
			mvi	HCNT[0], 28;
			clr	HCNT[1];
			clr	HCNT[2];
			or	DFCNTRL, HDMAEN|FIFOFLUSH;
			call	dma_finish;
		}
		inc	TQINPOS;
		mvi	INTSTAT,CMDCMPLT ret;
	}

if ((ahc->flags & AHC_INITIATORMODE) != 0) {
initiator_select:
	mvi	SPIOEN call	initialize_channel;

	/*
	 * We aren't expecting a bus free, so interrupt
	 * the kernel driver if it happens.
	 */
	mvi	CLRSINT1,CLRBUSFREE;
	or	SIMODE1, ENBUSFREE;

	/*
	 * As soon as we get a successful selection, the target
	 * should go into the message out phase since we have ATN
	 * asserted.
	 */
	mvi	MSG_OUT, MSG_IDENTIFYFLAG;
	or	SEQ_FLAGS, IDENTIFY_SEEN;

	/*
	 * Main loop for information transfer phases.  Wait for the
	 * target to assert REQ before checking MSG, C/D and I/O for
	 * the bus phase.
	 */
ITloop:
	call	phase_lock;

	mov	A, LASTPHASE;

	test	A, ~P_DATAIN	jz p_data;
	cmp	A,P_COMMAND	je p_command;
	cmp	A,P_MESGOUT	je p_mesgout;
	cmp	A,P_STATUS	je p_status;
	cmp	A,P_MESGIN	je p_mesgin;

	mvi	INTSTAT,BAD_PHASE;
	jmp	ITloop;			/* Try reading the bus again. */

await_busfree:
	and	SIMODE1, ~ENBUSFREE;
	mov	NONE, SCSIDATL;		/* Ack the last byte */
	and	SXFRCTL0, ~SPIOEN;
	test	SSTAT1,REQINIT|BUSFREE	jz .;
	test	SSTAT1, BUSFREE jnz poll_for_work;
	mvi	INTSTAT, BAD_PHASE;
}

clear_target_state:
	/*
	 * We assume that the kernel driver may reset us
	 * at any time, even in the middle of a DMA, so
	 * clear DFCNTRL too.
	 */
	clr	DFCNTRL;

	/*
	 * We don't know the target we will connect to,
	 * so default to narrow transfers to avoid
	 * parity problems.
	 */
	if ((ahc->features & AHC_ULTRA2) != 0) {
		bmov	SCSIRATE, ALLZEROS, 2;
	} else {
		clr	SCSIRATE;
		and	SXFRCTL0, ~(FAST20);
	}
	mvi	LASTPHASE, P_BUSFREE;
	/* clear target specific flags */
	clr	SEQ_FLAGS ret;

/*
 * If we re-enter the data phase after going through another phase, the
 * STCNT may have been cleared, so restore it from the residual field.
 */
data_phase_reinit:
	if ((ahc->features & AHC_ULTRA2) != 0) {
		/*
		 * The preload circuitry requires us to
		 * reload the address too, so pull it from
		 * the shaddow address.
		 */
		bmov	HADDR, SHADDR, 4;
		bmov	HCNT, SCB_RESID_DCNT, 3;
	} else if ((ahc->features & AHC_CMD_CHAN) != 0) {
		bmov	STCNT, SCB_RESID_DCNT, 3;
	} else {
		mvi	DINDEX, STCNT;
		mvi	SCB_RESID_DCNT	call bcopy_3;
	}
	and	DATA_COUNT_ODD, 0x1, SCB_RESID_DCNT[0];
	jmp	data_phase_loop;

p_data:
	if ((ahc->features & AHC_ULTRA2) != 0) {
		mvi	DMAPARAMS, PRELOADEN|SCSIEN|HDMAEN;
	} else {
		mvi	DMAPARAMS, WIDEODD|SCSIEN|SDMAEN|HDMAEN|FIFORESET;
	}
	test	LASTPHASE, IOI jnz . + 2;
	or	DMAPARAMS, DIRECTION;
	call	assert;			/*
					 * Ensure entering a data
					 * phase is okay - seen identify, etc.
					 */
	if ((ahc->features & AHC_CMD_CHAN) != 0) {
		mvi	CCSGADDR, CCSGADDR_MAX;
	}
	test	SEQ_FLAGS, DPHASE	jnz data_phase_reinit;

	/* We have seen a data phase */
	or	SEQ_FLAGS, DPHASE;

	/*
	 * Initialize the DMA address and counter from the SCB.
	 * Also set SG_COUNT and SG_NEXT in memory since we cannot
	 * modify the values in the SCB itself until we see a
	 * save data pointers message.
	 */
	if ((ahc->features & AHC_CMD_CHAN) != 0) {
		bmov	HADDR, SCB_DATAPTR, 7;
	} else {
		mvi	DINDEX, HADDR;
		mvi	SCB_DATAPTR	call bcopy_7;
	}
	and	DATA_COUNT_ODD, 0x1, SCB_DATACNT[0];

	if ((ahc->features & AHC_ULTRA2) == 0) {
		if ((ahc->features & AHC_CMD_CHAN) != 0) {
			bmov	STCNT, HCNT, 3;
		} else {
			call	set_stcnt_from_hcnt;
		}
	}

	if ((ahc->features & AHC_CMD_CHAN) != 0) {
		bmov	SG_COUNT, SCB_SGCOUNT, 5;
	} else {
		mvi	DINDEX, SG_COUNT;
		mvi	SCB_SGCOUNT	call bcopy_5;
	}

data_phase_loop:
/* Guard against overruns */
	test	SG_COUNT, 0xff jnz data_phase_inbounds;
/*
 * Turn on 'Bit Bucket' mode, set the transfer count to
 * 16meg and let the target run until it changes phase.
 * When the transfer completes, notify the host that we
 * had an overrun.
 */
	or	SXFRCTL1,BITBUCKET;
	and	DMAPARAMS, ~(HDMAEN|SDMAEN);
	if ((ahc->features & AHC_ULTRA2) != 0) {
		bmov	HCNT, ALLONES, 3;
	} else if ((ahc->features & AHC_CMD_CHAN) != 0) {
		bmov	STCNT, ALLONES, 3;
	} else {
		mvi	STCNT[0], 0xFF;
		mvi	STCNT[1], 0xFF;
		mvi	STCNT[2], 0xFF;
	}
data_phase_inbounds:
/* If we are the last SG block, tell the hardware. */
	cmp	SG_COUNT,0x01 jne data_phase_wideodd;
	if ((ahc->features & AHC_ULTRA2) != 0) {
		or	SG_CACHEPTR, LAST_SEG;
	} else {
		if ((ahc->flags & AHC_TARGETMODE) != 0) {
			test	SSTAT0, TARGET jz . + 2;
			test	DMAPARAMS, DIRECTION jz data_phase_wideodd;
		}
		and	DMAPARAMS, ~WIDEODD;
	}
data_phase_wideodd:
	if ((ahc->features & AHC_ULTRA2) != 0) {
		mov	SINDEX, ALLONES;
		mov	DFCNTRL, DMAPARAMS;
		test	SSTAT0, SDONE jnz .;/* Wait for preload to complete */
data_phase_dma_loop:
		test	SSTAT0,	SDONE jnz data_phase_dma_done;
		test	SSTAT1,PHASEMIS	jz data_phase_dma_loop;	/* ie. underrun */
	} else {
		mov	DMAPARAMS  call dma;
	}

data_phase_dma_done:
/* Go tell the host about any overruns */
	test	SXFRCTL1,BITBUCKET jnz data_phase_overrun;

/* See if we completed this segment */
	test	STCNT[0], 0xff	jnz data_phase_finish;
	test	STCNT[1], 0xff	jnz data_phase_finish;
	test	STCNT[2], 0xff	jnz data_phase_finish;

/*
 * Advance the scatter-gather pointers if needed
 */
sg_advance:
	dec	SG_COUNT;	/* one less segment to go */

	test	SG_COUNT, 0xff	jz data_phase_finish; /* Are we done? */
/*
 * Load a struct scatter and set up the data address and length.
 * If the working value of the SG count is nonzero, then
 * we need to load a new set of values.
 *
 * This, like all DMA's, assumes little-endian host data storage.
 */
sg_load:
	if ((ahc->features & AHC_CMD_CHAN) != 0) {
		/*
		 * Do we have any prefetch left???
		 */
		cmp	CCSGADDR, CCSGADDR_MAX jne prefetched_segs_avail;

		/*
		 * Fetch MIN(CCSGADDR_MAX, (SG_COUNT * 8)) bytes.
		 */
		add	A, -(CCSGRAM_MAXSEGS + 1), SG_COUNT;
		mvi	A, CCSGADDR_MAX;
		jc	. + 2;
		shl	A, 3, SG_COUNT;
		mov	CCHCNT, A;
		bmov	CCHADDR, SG_NEXT, 4;
		mvi	CCSGCTL, CCSGEN|CCSGRESET;
		test	CCSGCTL, CCSGDONE jz .;
		and	CCSGCTL, ~CCSGEN;
		test	CCSGCTL, CCSGEN jnz .;
		mvi	CCSGCTL, CCSGRESET;
prefetched_segs_avail:
		bmov 	HADDR, CCSGRAM, 8;
	} else {
		mvi	DINDEX, HADDR;
		mvi	SG_NEXT	call bcopy_4;

		mvi	HCNT[0],SG_SIZEOF;
		clr	HCNT[1];
		clr	HCNT[2];

		or	DFCNTRL, HDMAEN|DIRECTION|FIFORESET;

		call	dma_finish;

		/*
		 * Copy data from FIFO into SCB data pointer and data count.
		 * This assumes that the SG segments are of the form:
		 * struct ahc_dma_seg {
		 *	u_int32_t	addr;	four bytes, little-endian order
		 *	u_int32_t	len;	four bytes, little endian order
		 * };
		 */
		mvi	HADDR	call dfdat_in_7;
	}

	/* Track odd'ness */
	test	HCNT[0], 0x1 jz . + 2;
	xor	DATA_COUNT_ODD, 0x1;

	if ((ahc->features & AHC_ULTRA2) == 0) {
		/* Load STCNT as well.  It is a mirror of HCNT */
		if ((ahc->features & AHC_CMD_CHAN) != 0) {
			bmov	STCNT, HCNT, 3;
		} else {
			call	set_stcnt_from_hcnt;
		}
	}

/* Advance the SG pointer */
	clr	A;			/* add sizeof(struct scatter) */
	add	SG_NEXT[0],SG_SIZEOF;
	adc	SG_NEXT[1],A;

	if ((ahc->flags & AHC_TARGETMODE) != 0) {
		test	SSTAT0, TARGET jnz data_phase_loop;
	}
	test	SSTAT1, REQINIT jz .;
	test	SSTAT1,PHASEMIS	jz data_phase_loop;

	/* Ensure the last seg is visable at the shaddow layer */
	if ((ahc->features & AHC_ULTRA2) != 0) {
		mov	DFCNTRL, DMAPARAMS;
		test	SSTAT0, SDONE jnz .;/* Wait for preload to complete */
	}

data_phase_finish:
	if ((ahc->features & AHC_ULTRA2) != 0) {
		call	ultra2_dmafinish;
	}
/*
 * After a DMA finishes, save the SG and STCNT residuals back into the SCB
 * We use STCNT instead of HCNT, since it's a reflection of how many bytes
 * were transferred on the SCSI (as opposed to the host) bus.
 */
	if ((ahc->features & AHC_CMD_CHAN) != 0) {
		bmov	SCB_RESID_DCNT, STCNT, 3;
	} else {
		mov	SCB_RESID_DCNT[0],STCNT[0];
		mov	SCB_RESID_DCNT[1],STCNT[1];
		mov	SCB_RESID_DCNT[2],STCNT[2];
	}
	mov	SCB_RESID_SGCNT, SG_COUNT;

	if ((ahc->features & AHC_ULTRA2) != 0) {
		or	SXFRCTL0, CLRSTCNT|CLRCHN;
	}

	if ((ahc->flags & AHC_TARGETMODE) != 0) {
		test	SEQ_FLAGS, DPHASE_PENDING jz ITloop;
		and	SEQ_FLAGS, ~DPHASE_PENDING;
		/*
		 * For data-in phases, wait for any pending acks from the
		 * initiator before changing phase.
		 */
		test	DFCNTRL, DIRECTION jz target_ITloop;
		test	SSTAT1, REQINIT	jnz .;
		jmp	target_ITloop;
	}
	jmp	ITloop;

data_phase_overrun:
	if ((ahc->features & AHC_ULTRA2) != 0) {
		call	ultra2_dmafinish;
		or	SXFRCTL0, CLRSTCNT|CLRCHN;
	}
/*
 * Turn off BITBUCKET mode and notify the host
 */
	and	SXFRCTL1, ~BITBUCKET;
	mvi	INTSTAT,DATA_OVERRUN;
	jmp	ITloop;

ultra2_dmafinish:
	if ((ahc->features & AHC_ULTRA2) != 0) {
		test	DFCNTRL, DIRECTION jnz ultra2_dmafifoempty;
		and	DFCNTRL, ~SCSIEN;
		test	DFCNTRL, SCSIEN jnz .;
ultra2_dmafifoflush:
		or	DFCNTRL, FIFOFLUSH;
		/*
		 * The FIFOEMP status bit on the Ultra2 class
		 * of controllers seems to be a bit flaky.
		 * It appears that if the FIFO is full and the
		 * transfer ends with some data in the REQ/ACK
		 * FIFO, FIFOEMP will fall temporarily
		 * as the data is transferred to the PCI bus.
		 * This glitch lasts for fewer than 5 clock cycles,
		 * so we work around the problem by ensuring the
		 * status bit stays false through a full glitch
		 * window.
		 */
		test	DFSTATUS, FIFOEMP jz ultra2_dmafifoflush;
		test	DFSTATUS, FIFOEMP jz ultra2_dmafifoflush;
		test	DFSTATUS, FIFOEMP jz ultra2_dmafifoflush;
		test	DFSTATUS, FIFOEMP jz ultra2_dmafifoflush;
		test	DFSTATUS, FIFOEMP jz ultra2_dmafifoflush;

ultra2_dmafifoempty:
		/* Don't clobber an inprogress host data transfer */
		test	DFSTATUS, MREQPEND	jnz ultra2_dmafifoempty;

ultra2_dmahalt:
		and     DFCNTRL, ~(SCSIEN|HDMAEN);
		test	DFCNTRL, HDMAEN jnz .;
		ret;
	}

if ((ahc->flags & AHC_INITIATORMODE) != 0) {
/*
 * Command phase.  Set up the DMA registers and let 'er rip.
 */
p_command:
	call	assert;

	if ((ahc->features & AHC_CMD_CHAN) != 0) {
		mov	HCNT[0], SCB_CMDLEN;
		bmov	HCNT[1], ALLZEROS, 2;
		if ((ahc->features & AHC_ULTRA2) == 0) {
			bmov	STCNT, HCNT, 3;
		}
		add	NONE, -17, SCB_CMDLEN;
		jc	dma_cmd_data;
		/*
		 * The data fifo seems to require 4 byte alligned
		 * transfers from the sequencer.  Force this to
		 * be the case by clearing HADDR[0] even though
		 * we aren't going to touch host memeory.
		 */
		bmov	HADDR[0], ALLZEROS, 1;
		if ((ahc->features & AHC_ULTRA2) != 0) {
			mvi	DFCNTRL, (PRELOADEN|SCSIEN|DIRECTION);
		} else {
			mvi	DFCNTRL, (SCSIEN|SDMAEN|DIRECTION|FIFORESET);
		}
		bmov   DFDAT, SCB_CMDSTORE, 16;
		jmp	cmd_loop;
dma_cmd_data:
		bmov	HADDR, SCB_CMDPTR, 4;
	} else {
		mvi	DINDEX, HADDR;
		mvi	SCB_CMDPTR	call bcopy_5;
		clr	HCNT[1];
		clr	HCNT[2];
	}

	if ((ahc->features & AHC_ULTRA2) == 0) {
		if ((ahc->features & AHC_CMD_CHAN) == 0) {
			call	set_stcnt_from_hcnt;
		}
		mvi	DFCNTRL, (SCSIEN|SDMAEN|HDMAEN|DIRECTION|FIFORESET);
	} else {
		mvi	DFCNTRL, (PRELOADEN|SCSIEN|HDMAEN|DIRECTION);
	}
cmd_loop:
	test	SSTAT0, SDONE jnz . + 2;
	test    SSTAT1, PHASEMIS jz cmd_loop;
	/*
	 * Wait for our ACK to go-away on it's own
	 * instead of being killed by SCSIEN getting cleared.
	 */
	test	SCSISIGI, ACKI jnz .;
	and	DFCNTRL, ~(SCSIEN|SDMAEN|HDMAEN);
	test	DFCNTRL, (SCSIEN|SDMAEN|HDMAEN) jnz .;
	jmp	ITloop;

/*
 * Status phase.  Wait for the data byte to appear, then read it
 * and store it into the SCB.
 */
p_status:
	call	assert;

	mov	SCB_TARGET_STATUS, SCSIDATL;
	jmp	ITloop;

/*
 * Message out phase.  If MSG_OUT is MSG_IDENTIFYFLAG, build a full
 * indentify message sequence and send it to the target.  The host may
 * override this behavior by setting the MK_MESSAGE bit in the SCB
 * control byte.  This will cause us to interrupt the host and allow
 * it to handle the message phase completely on its own.  If the bit
 * associated with this target is set, we will also interrupt the host,
 * thereby allowing it to send a message on the next selection regardless
 * of the transaction being sent.
 *
 * If MSG_OUT is == HOST_MSG, also interrupt the host and take a message.
 * This is done to allow the host to send messages outside of an identify
 * sequence while protecting the seqencer from testing the MK_MESSAGE bit
 * on an SCB that might not be for the current nexus. (For example, a
 * BDR message in responce to a bad reselection would leave us pointed to
 * an SCB that doesn't have anything to do with the current target).
 *
 * Otherwise, treat MSG_OUT as a 1 byte message to send (abort, abort tag,
 * bus device reset).
 *
 * When there are no messages to send, MSG_OUT should be set to MSG_NOOP,
 * in case the target decides to put us in this phase for some strange
 * reason.
 */
p_mesgout_retry:
	or	SCSISIGO,ATNO,LASTPHASE;/* turn on ATN for the retry */
p_mesgout:
	mov	SINDEX, MSG_OUT;
	cmp	SINDEX, MSG_IDENTIFYFLAG jne p_mesgout_from_host;
	test	SCB_CONTROL,MK_MESSAGE	jnz host_message_loop;
	mov	FUNCTION1, SCB_TCL;
	mov	A, FUNCTION1;
	if ((ahc->features & AHC_HS_MAILBOX) != 0) {
		/*
		 * Work around a pausing bug in at least the aic7890.
		 * If the host needs to update the TARGET_MSG_REQUEST
		 * bit field, it will set the HS_MAILBOX to 1.  In
		 * response, we pause with a specific interrupt code
		 * asking for the mask to be updated before we continue.
		 * Ugh.
		 */
		test	HS_MAILBOX, 0xF0	jz . + 2;
		mvi	INTSTAT, UPDATE_TMSG_REQ;
		nop;
	}
	mov	SINDEX, TARGET_MSG_REQUEST[0];
	if ((ahc->features & AHC_TWIN) != 0) {
		/* Second Channel uses high byte bits */
		test	SCB_TCL, SELBUSB	jz . + 2;
		mov	SINDEX, TARGET_MSG_REQUEST[1];
	} else if ((ahc->features & AHC_WIDE) != 0) {
		test	SCB_TCL, 0x80		jz . + 2; /* target > 7 */
		mov	SINDEX, TARGET_MSG_REQUEST[1];
	}
	test	SINDEX, A	jnz host_message_loop;
p_mesgout_identify:
	and	SINDEX,LID,SCB_TCL;	/* lun */
	and	A,DISCENB,SCB_CONTROL;	/* mask off disconnect privledge */
	or	SINDEX,A;		/* or in disconnect privledge */
	or	SINDEX,MSG_IDENTIFYFLAG;
/*
 * Send a tag message if TAG_ENB is set in the SCB control block.
 * Use SCB_TAG (the position in the kernel's SCB array) as the tag value.
 */
p_mesgout_tag:
	test	SCB_CONTROL,TAG_ENB jz  p_mesgout_onebyte;
	mov	SCSIDATL, SINDEX;	/* Send the identify message */
	call	phase_lock;
	cmp	LASTPHASE, P_MESGOUT	jne p_mesgout_done;
	and	SCSIDATL,TAG_ENB|SCB_TAG_TYPE,SCB_CONTROL;
	call	phase_lock;
	cmp	LASTPHASE, P_MESGOUT	jne p_mesgout_done;
	mov	SCB_TAG	jmp p_mesgout_onebyte;
/*
 * Interrupt the driver, and allow it to handle this message
 * phase and any required retries.
 */
p_mesgout_from_host:
	cmp	SINDEX, HOST_MSG	jne p_mesgout_onebyte;
	jmp	host_message_loop;

p_mesgout_onebyte:
	mvi	CLRSINT1, CLRATNO;
	mov	SCSIDATL, SINDEX;

/*
 * If the next bus phase after ATN drops is message out, it means
 * that the target is requesting that the last message(s) be resent.
 */
	call	phase_lock;
	cmp	LASTPHASE, P_MESGOUT	je p_mesgout_retry;

p_mesgout_done:
	mvi	CLRSINT1,CLRATNO;	/* Be sure to turn ATNO off */
	mov	LAST_MSG, MSG_OUT;
	mvi	MSG_OUT, MSG_NOOP;	/* No message left */
	jmp	ITloop;

/*
 * Message in phase.  Bytes are read using Automatic PIO mode.
 */
p_mesgin:
	mvi	ACCUM		call inb_first;	/* read the 1st message byte */

	test	A,MSG_IDENTIFYFLAG	jnz mesgin_identify;
	cmp	A,MSG_DISCONNECT	je mesgin_disconnect;
	cmp	A,MSG_SAVEDATAPOINTER	je mesgin_sdptrs;
	cmp	ALLZEROS,A		je mesgin_complete;
	cmp	A,MSG_RESTOREPOINTERS	je mesgin_rdptrs;
	cmp	A,MSG_NOOP		je mesgin_done;

/*
 * Pushed message loop to allow the kernel to
 * run it's own message state engine.  To avoid an
 * extra nop instruction after signaling the kernel,
 * we perform the phase_lock before checking to see
 * if we should exit the loop and skip the phase_lock
 * in the ITloop.  Performing back to back phase_locks
 * shouldn't hurt, but why do it twice...
 */
host_message_loop:
	mvi	INTSTAT, HOST_MSG_LOOP;
	call	phase_lock;
	cmp	RETURN_1, EXIT_MSG_LOOP	je ITloop + 1;
	jmp	host_message_loop;

mesgin_done:
	mov	NONE,SCSIDATL;		/*dummy read from latch to ACK*/
	jmp	ITloop;


mesgin_complete:
/*
 * We got a "command complete" message, so put the SCB_TAG into the QOUTFIFO,
 * and trigger a completion interrupt.  Before doing so, check to see if there
 * is a residual or the status byte is something other than STATUS_GOOD (0).
 * In either of these conditions, we upload the SCB back to the host so it can
 * process this information.  In the case of a non zero status byte, we
 * additionally interrupt the kernel driver synchronously, allowing it to
 * decide if sense should be retrieved.  If the kernel driver wishes to request
 * sense, it will fill the kernel SCB with a request sense command and set
 * RETURN_1 to SEND_SENSE.  If RETURN_1 is set to SEND_SENSE we redownload
 * the SCB, and process it as the next command by adding it to the waiting list.
 * If the kernel driver does not wish to request sense, it need only clear
 * RETURN_1, and the command is allowed to complete normally.  We don't bother
 * to post to the QOUTFIFO in the error cases since it would require extra
 * work in the kernel driver to ensure that the entry was removed before the
 * command complete code tried processing it.
 */

/*
 * First check for residuals
 */
	test	SCB_RESID_SGCNT,0xff	jnz upload_scb;
	test	SCB_TARGET_STATUS,0xff	jz complete;	/* Good Status? */
upload_scb:
	mvi	DMAPARAMS, FIFORESET;
	mov	SCB_TAG		call dma_scb;
check_status:
	test	SCB_TARGET_STATUS,0xff	jz complete;	/* Just a residual? */
	mvi	INTSTAT,BAD_STATUS;			/* let driver know */
	nop;
	cmp	RETURN_1, SEND_SENSE	jne complete;
	/* This SCB becomes the next to execute as it will retrieve sense */
	mvi	DMAPARAMS, HDMAEN|DIRECTION|FIFORESET;
	mov	SCB_TAG		call dma_scb;
add_to_waiting_list:
	mov	SCB_NEXT,WAITING_SCBH;
	mov	WAITING_SCBH, SCBPTR;
	/*
	 * Prepare our selection hardware before the busfree so we have a
	 * high probability of winning arbitration.
	 */
	call	start_selection;
	jmp	await_busfree;

complete:
	/* If we are untagged, clear our address up in host ram */
	test	SCB_CONTROL, TAG_ENB jnz complete_queue;
	mov	A, SAVED_TCL;
	mvi	UNTAGGEDSCB_OFFSET call post_byte_setup;
	mvi	SCB_LIST_NULL call post_byte;

complete_queue:
	mov	SCB_TAG call complete_post;
	jmp	await_busfree;
}

complete_post:
	/* Post the SCBID in SINDEX and issue an interrupt */
	call	add_scb_to_free_list;
	mov	ARG_1, SINDEX;
	if ((ahc->features & AHC_QUEUE_REGS) != 0) {
		mov	A, SDSCB_QOFF;
	} else {
		mov	A, QOUTPOS;
	}
	mvi	QOUTFIFO_OFFSET call post_byte_setup;
	mov	ARG_1 call post_byte;
	if ((ahc->features & AHC_QUEUE_REGS) == 0) {
		inc 	QOUTPOS;
	}
	mvi	INTSTAT,CMDCMPLT ret;

if ((ahc->flags & AHC_INITIATORMODE) != 0) {
/*
 * Is it a disconnect message?  Set a flag in the SCB to remind us
 * and await the bus going free.
 */
mesgin_disconnect:
	or	SCB_CONTROL,DISCONNECTED;
	call	add_scb_to_disc_list;
	jmp	await_busfree;

/*
 * Save data pointers message:
 * Copying RAM values back to SCB, for Save Data Pointers message, but
 * only if we've actually been into a data phase to change them.  This
 * protects against bogus data in scratch ram and the residual counts
 * since they are only initialized when we go into data_in or data_out.
 */
mesgin_sdptrs:
	test	SEQ_FLAGS, DPHASE	jz mesgin_done;

	/*
	 * The SCB SGPTR becomes the next one we'll download,
	 * and the SCB DATAPTR becomes the current SHADDR.
	 * Use the residual number since STCNT is corrupted by
	 * any message transfer.
	 */
	if ((ahc->features & AHC_CMD_CHAN) != 0) {
		bmov	SCB_SGCOUNT, SG_COUNT, 5;
		bmov	SCB_DATAPTR, SHADDR, 4;
		bmov	SCB_DATACNT, SCB_RESID_DCNT, 3;
	} else {
		mvi	DINDEX, SCB_SGCOUNT;
		mvi	SG_COUNT call bcopy_5;

		mvi	DINDEX, SCB_DATAPTR;
		mvi	SHADDR		call bcopy_4;
		mvi	SCB_RESID_DCNT	call bcopy_3;
	}
	jmp	mesgin_done;

/*
 * Restore pointers message?  Data pointers are recopied from the
 * SCB anytime we enter a data phase for the first time, so all
 * we need to do is clear the DPHASE flag and let the data phase
 * code do the rest.
 */
mesgin_rdptrs:
	and	SEQ_FLAGS, ~DPHASE;		/*
						 * We'll reload them
						 * the next time through
						 * the dataphase.
						 */
	jmp	mesgin_done;

/*
 * Identify message?  For a reconnecting target, this tells us the lun
 * that the reconnection is for - find the correct SCB and switch to it,
 * clearing the "disconnected" bit so we don't "find" it by accident later.
 */
mesgin_identify:
	if ((ahc->features & AHC_WIDE) != 0) {
		and	A,0x0f;		/* lun in lower four bits */
	} else {
		and	A,0x07;		/* lun in lower three bits */
	}
	or      SAVED_TCL,A;		/* SAVED_TCL should be complete now */

	mvi	ARG_2, SCB_LIST_NULL;	/* SCBID of prev SCB in disc List */
	call	get_untagged_SCBID;
	cmp	ARG_1, SCB_LIST_NULL	je snoop_tag;
	if ((ahc->flags & AHC_PAGESCBS) != 0) {
		test	SEQ_FLAGS, SCBPTR_VALID	jz use_retrieveSCB;
	}
	/*
	 * If the SCB was found in the disconnected list (as is
	 * always the case in non-paging scenarios), SCBPTR is already
	 * set to the correct SCB.  So, simply setup the SCB and get
	 * on with things.
	 */
	call	rem_scb_from_disc_list;
	jmp	setup_SCB;
/*
 * Here we "snoop" the bus looking for a SIMPLE QUEUE TAG message.
 * If we get one, we use the tag returned to find the proper
 * SCB.  With SCB paging, this requires using search for both tagged
 * and non-tagged transactions since the SCB may exist in any slot.
 * If we're not using SCB paging, we can use the tag as the direct
 * index to the SCB.
 */
snoop_tag:
	mov	NONE,SCSIDATL;		/* ACK Identify MSG */
snoop_tag_loop:
	call	phase_lock;
	cmp	LASTPHASE, P_MESGIN	jne not_found;
	cmp	SCSIBUSL,MSG_SIMPLE_Q_TAG jne not_found;
get_tag:
	mvi	ARG_1	call inb_next;	/* tag value */

	/*
	 * Ensure that the SCB the tag points to is for
	 * an SCB transaction to the reconnecting target.
	 */
use_retrieveSCB:
	call	retrieveSCB;
setup_SCB:
	mov	A, SAVED_TCL;
	cmp	SCB_TCL, A	jne not_found_cleanup_scb;
	test	SCB_CONTROL,DISCONNECTED jz not_found_cleanup_scb;
	and	SCB_CONTROL,~DISCONNECTED;
	or	SEQ_FLAGS,IDENTIFY_SEEN;	/* make note of IDENTIFY */
	call	set_transfer_settings;
	/* See if the host wants to send a message upon reconnection */
	test	SCB_CONTROL, MK_MESSAGE jz mesgin_done;
	and	SCB_CONTROL, ~MK_MESSAGE;
	mvi	HOST_MSG	call mk_mesg;
	jmp	mesgin_done;

not_found_cleanup_scb:
	test	SCB_CONTROL, DISCONNECTED jz . + 3;
	call	add_scb_to_disc_list;
	jmp	not_found;
	call	add_scb_to_free_list;
not_found:
	mvi	INTSTAT, NO_MATCH;
	jmp	mesgin_done;

/*
 * [ ADD MORE MESSAGE HANDLING HERE ]
 */

/*
 * Locking the driver out, build a one-byte message passed in SINDEX
 * if there is no active message already.  SINDEX is returned intact.
 */
mk_mesg:
	or	SCSISIGO,ATNO,LASTPHASE;/* turn on ATNO */
	mov	MSG_OUT,SINDEX ret;

/*
 * Functions to read data in Automatic PIO mode.
 *
 * According to Adaptec's documentation, an ACK is not sent on input from
 * the target until SCSIDATL is read from.  So we wait until SCSIDATL is
 * latched (the usual way), then read the data byte directly off the bus
 * using SCSIBUSL.  When we have pulled the ATN line, or we just want to
 * acknowledge the byte, then we do a dummy read from SCISDATL.  The SCSI
 * spec guarantees that the target will hold the data byte on the bus until
 * we send our ACK.
 *
 * The assumption here is that these are called in a particular sequence,
 * and that REQ is already set when inb_first is called.  inb_{first,next}
 * use the same calling convention as inb.
 */
inb_next_wait_perr:
	mvi	INTSTAT, PERR_DETECTED;
	jmp	inb_next_wait;
inb_next:
	mov	NONE,SCSIDATL;		/*dummy read from latch to ACK*/
inb_next_wait:
	/*
	 * If there is a parity error, wait for the kernel to
	 * see the interrupt and prepare our message response
	 * before continuing.
	 */
	test	SSTAT1, REQINIT	jz inb_next_wait;
	test	SSTAT1, SCSIPERR jnz inb_next_wait_perr;
inb_next_check_phase:
	and	LASTPHASE, PHASE_MASK, SCSISIGI;
	cmp	LASTPHASE, P_MESGIN jne mesgin_phasemis;
inb_first:
	mov	DINDEX,SINDEX;
	mov	DINDIR,SCSIBUSL	ret;		/*read byte directly from bus*/
inb_last:
	mov	NONE,SCSIDATL ret;		/*dummy read from latch to ACK*/
}

if ((ahc->flags & AHC_TARGETMODE) != 0) {
/*
 * Change to a new phase.  If we are changing the state of the I/O signal,
 * from out to in, wait an additional data release delay before continuing.
 */
change_phase:
	/* Wait for preceeding I/O session to complete. */
	test	SCSISIGI, ACKI jnz .;

	/* Change the phase */
	and	DINDEX, IOI, SCSISIGI;
	mov	SCSISIGO, SINDEX;
	and	A, IOI, SINDEX;

	/*
	 * If the data direction has changed, from
	 * out (initiator driving) to in (target driving),
	 * we must waitat least a data release delay plus
	 * the normal bus settle delay. [SCSI III SPI 10.11.0]
	 */
	cmp 	DINDEX, A je change_phase_wait;
	test	SINDEX, IOI jz change_phase_wait;
	call	change_phase_wait;
change_phase_wait:
	nop;
	nop;
	nop;
	nop ret;

/*
 * Send a byte to an initiator in Automatic PIO mode.
 */
target_outb:
	or	SXFRCTL0, SPIOEN;
	test	SSTAT0, SPIORDY	jz .;
	mov	SCSIDATL, SINDEX;
	test	SSTAT0, SPIORDY	jz .;
	and	SXFRCTL0, ~SPIOEN ret;
}

mesgin_phasemis:
/*
 * We expected to receive another byte, but the target changed phase
 */
	mvi	INTSTAT, MSGIN_PHASEMIS;
	jmp	ITloop;

/*
 * DMA data transfer.  HADDR and HCNT must be loaded first, and
 * SINDEX should contain the value to load DFCNTRL with - 0x3d for
 * host->scsi, or 0x39 for scsi->host.  The SCSI channel is cleared
 * during initialization.
 */
dma:
	mov	DFCNTRL,SINDEX;
dma_loop:
	test	SSTAT0,DMADONE	jnz dma_dmadone;
	test	SSTAT1,PHASEMIS	jz dma_loop;	/* ie. underrun */
dma_phasemis:

/*
 * We will be "done" DMAing when the transfer count goes to zero, or
 * the target changes the phase (in light of this, it makes sense that
 * the DMA circuitry doesn't ACK when PHASEMIS is active).  If we are
 * doing a SCSI->Host transfer, the data FIFO should be flushed auto-
 * magically on STCNT=0 or a phase change, so just wait for FIFO empty
 * status.
 */
dma_checkfifo:
	test	DFCNTRL,DIRECTION	jnz dma_fifoempty;
dma_fifoflush:
	test	DFSTATUS,FIFOEMP	jz dma_fifoflush;

dma_fifoempty:
	/* Don't clobber an inprogress host data transfer */
	test	DFSTATUS, MREQPEND	jnz dma_fifoempty;
/*
 * Now shut the DMA enables off and make sure that the DMA enables are
 * actually off first lest we get an ILLSADDR.
 */
dma_dmadone:
	and	DFCNTRL, ~(SCSIEN|SDMAEN|HDMAEN);
dma_halt:
	/*
	 * Some revisions of the aic7880 have a problem where, if the
	 * data fifo is full, but the PCI input latch is not empty,
	 * HDMAEN cannot be cleared.  The fix used here is to attempt
	 * to drain the data fifo until there is space for the input
	 * latch to drain and HDMAEN de-asserts.
	 */
	if ((ahc->features & AHC_ULTRA2) == 0) {
		mov	NONE, DFDAT;
	}
	test	DFCNTRL, (SCSIEN|SDMAEN|HDMAEN) jnz dma_halt;
return:
	ret;

/*
 * Assert that if we've been reselected, then we've seen an IDENTIFY
 * message.
 */
assert:
	test	SEQ_FLAGS,IDENTIFY_SEEN	jnz return;	/* seen IDENTIFY? */

	mvi	INTSTAT,NO_IDENT 	ret;	/* no - tell the kernel */

/*
 * Locate a disconnected SCB either by SAVED_TCL (ARG_1 is SCB_LIST_NULL)
 * or by the SCBID ARG_1.  The search begins at the SCB index passed in
 * via SINDEX which is an SCB that must be on the disconnected list.  If
 * the SCB cannot be found, SINDEX will be SCB_LIST_NULL, otherwise, SCBPTR
 * is set to the proper SCB.
 */
findSCB:
	mov	SCBPTR,SINDEX;			/* Initialize SCBPTR */
	cmp	ARG_1, SCB_LIST_NULL	jne findSCB_by_SCBID;
	mov	A, SAVED_TCL;
	mvi	SCB_TCL	jmp findSCB_loop;	/* &SCB_TCL -> SINDEX */
findSCB_by_SCBID:
	mov	A, ARG_1;			/* Tag passed in ARG_1 */
	mvi	SCB_TAG	jmp findSCB_loop;	/* &SCB_TAG -> SINDEX */
findSCB_next:
	mov	ARG_2, SCBPTR;
	cmp	SCB_NEXT, SCB_LIST_NULL je notFound;
	mov	SCBPTR,SCB_NEXT;
	dec	SINDEX;		/* Last comparison moved us too far */
findSCB_loop:
	cmp	SINDIR, A	jne findSCB_next;
	mov	SINDEX, SCBPTR 	ret;
notFound:
	mvi	SINDEX, SCB_LIST_NULL	ret;

/*
 * Retrieve an SCB by SCBID first searching the disconnected list falling
 * back to DMA'ing the SCB down from the host.  This routine assumes that
 * ARG_1 is the SCBID of interrest and that SINDEX is the position in the
 * disconnected list to start the search from.  If SINDEX is SCB_LIST_NULL,
 * we go directly to the host for the SCB.
 */
retrieveSCB:
	test	SEQ_FLAGS, SCBPTR_VALID	jz retrieve_from_host;
	mov	SCBPTR	call findSCB;	/* Continue the search */
	cmp	SINDEX, SCB_LIST_NULL	je retrieve_from_host;

/*
 * This routine expects SINDEX to contain the index of the SCB to be
 * removed, SCBPTR to be pointing to that SCB, and ARG_2 to be the
 * SCBID of the SCB just previous to this one in the list or SCB_LIST_NULL
 * if it is at the head.
 */
rem_scb_from_disc_list:
/* Remove this SCB from the disconnection list */
	cmp	ARG_2, SCB_LIST_NULL	je rHead;
	mov	DINDEX, SCB_NEXT;
	mov	SCBPTR, ARG_2;
	mov	SCB_NEXT, DINDEX;
	mov	SCBPTR, SINDEX ret;
rHead:
	mov	DISCONNECTED_SCBH,SCB_NEXT ret;

retrieve_from_host:
/*
 * We didn't find it.  Pull an SCB and DMA down the one we want.
 * We should never get here in the non-paging case.
 */
	mov	ALLZEROS	call	get_free_or_disc_scb;
	mvi	DMAPARAMS, HDMAEN|DIRECTION|FIFORESET;
	/* Jump instead of call as we want to return anyway */
	mov	ARG_1	jmp dma_scb;

/*
 * Determine whether a target is using tagged or non-tagged transactions
 * by first looking for a matching transaction based on the TCL and if
 * that fails, looking up this device in the host's untagged SCB array.
 * The TCL to search for is assumed to be in SAVED_TCL.  The value is
 * returned in ARG_1 (SCB_LIST_NULL for tagged, SCBID for non-tagged).
 * The SCBPTR_VALID bit is set in SEQ_FLAGS if we found the information
 * in an SCB instead of having to go to the host.
 */
get_untagged_SCBID:
	cmp	DISCONNECTED_SCBH, SCB_LIST_NULL je get_SCBID_from_host;
	mvi	ARG_1, SCB_LIST_NULL;
	mov	DISCONNECTED_SCBH call findSCB;
	cmp	SINDEX, SCB_LIST_NULL	je get_SCBID_from_host;
	or	SEQ_FLAGS, SCBPTR_VALID;/* Was in disconnected list */
	test	SCB_CONTROL, TAG_ENB	jnz . + 2;
	mov	ARG_1, SCB_TAG	ret;
	mvi	ARG_1, SCB_LIST_NULL ret;

/*
 * Fetch a byte from host memory given an index of (A + (256 * SINDEX))
 * and a base address of SCBID_ADDR.  The byte is returned in RETURN_2.
 */
fetch_byte:
	mov	ARG_2, SINDEX;
	if ((ahc->features & AHC_CMD_CHAN) != 0) {
		mvi	DINDEX, CCHADDR;
		mvi	SCBID_ADDR call set_1byte_addr;
		mvi	CCHCNT, 1;
		mvi	CCSGCTL, CCSGEN|CCSGRESET;
		test	CCSGCTL, CCSGDONE jz .;
		mvi	CCSGCTL, CCSGRESET;
		bmov	RETURN_2, CCSGRAM, 1 ret;
	} else {
		mvi	DINDEX, HADDR;
		mvi	SCBID_ADDR call set_1byte_addr;
		mvi	HCNT[0], 1;
		clr	HCNT[1];
		clr	HCNT[2];
		mvi	DFCNTRL, HDMAEN|DIRECTION|FIFORESET;
		call	dma_finish;
		mov	RETURN_2, DFDAT ret;
	}

/*
 * Prepare the hardware to post a byte to host memory given an
 * index of (A + (256 * SINDEX)) and a base address of SCBID_ADDR.
 */
post_byte_setup:
	mov	ARG_2, SINDEX;
	if ((ahc->features & AHC_CMD_CHAN) != 0) {
		mvi	DINDEX, CCHADDR;
		mvi	SCBID_ADDR call	set_1byte_addr;
		mvi	CCHCNT, 1;
		mvi	CCSCBCTL, CCSCBRESET ret;
	} else {
		mvi	DINDEX, HADDR;
		mvi	SCBID_ADDR call	set_1byte_addr;
		mvi	HCNT[0], 1;
		clr	HCNT[1];
		clr	HCNT[2];
		mvi	DFCNTRL, FIFORESET ret;
	}

post_byte:
	if ((ahc->features & AHC_CMD_CHAN) != 0) {
		bmov	CCSCBRAM, SINDEX, 1;
		or	CCSCBCTL, CCSCBEN|CCSCBRESET;
		test	CCSCBCTL, CCSCBDONE jz .;
		clr	CCSCBCTL ret;
	} else {
		mov	DFDAT, SINDEX;
		or	DFCNTRL, HDMAEN|FIFOFLUSH;
		jmp	dma_finish;
	}

get_SCBID_from_host:
	mov	A, SAVED_TCL;
	mvi	UNTAGGEDSCB_OFFSET call fetch_byte;
	mov	RETURN_1,  RETURN_2 ret;

phase_lock_perr:
	mvi	INTSTAT, PERR_DETECTED;
phase_lock:
	/*
	 * If there is a parity error, wait for the kernel to
	 * see the interrupt and prepare our message response
	 * before continuing.
	 */
	test	SSTAT1, REQINIT jz phase_lock;
	test	SSTAT1, SCSIPERR jnz phase_lock_perr;
phase_lock_latch_phase:
	and	SCSISIGO, PHASE_MASK, SCSISIGI;
	and	LASTPHASE, PHASE_MASK, SCSISIGI ret;

if ((ahc->features & AHC_CMD_CHAN) == 0) {
set_stcnt_from_hcnt:
	mov	STCNT[0], HCNT[0];
	mov	STCNT[1], HCNT[1];
	mov	STCNT[2], HCNT[2] ret;

bcopy_7:
	mov	DINDIR, SINDIR;
	mov	DINDIR, SINDIR;
bcopy_5:
	mov	DINDIR, SINDIR;
bcopy_4:
	mov	DINDIR, SINDIR;
bcopy_3:
	mov	DINDIR, SINDIR;
	mov	DINDIR, SINDIR;
	mov	DINDIR, SINDIR ret;
}

if ((ahc->flags & AHC_TARGETMODE) != 0) {
/*
 * Setup addr assuming that A is an index into
 * an array of 32byte objects, SINDEX contains
 * the base address of that array, and DINDEX
 * contains the base address of the location
 * to store the indexed address.
 */
set_32byte_addr:
	shr	ARG_2, 3, A;
	shl	A, 5;
	jmp	set_1byte_addr;
}

/*
 * Setup addr assuming that A is an index into
 * an array of 64byte objects, SINDEX contains
 * the base address of that array, and DINDEX
 * contains the base address of the location
 * to store the indexed address.
 */
set_64byte_addr:
	shr	ARG_2, 2, A;
	shl	A, 6;

/*
 * Setup addr assuming that A + (ARG_1 * 256) is an
 * index into an array of 1byte objects, SINDEX contains
 * the base address of that array, and DINDEX contains
 * the base address of the location to store the computed
 * address.
 */
set_1byte_addr:
	add     DINDIR, A, SINDIR;
	mov     A, ARG_2;
	adc	DINDIR, A, SINDIR;
	clr	A;
	adc	DINDIR, A, SINDIR;
	adc	DINDIR, A, SINDIR ret;

/*
 * Either post or fetch and SCB from host memory based on the
 * DIRECTION bit in DMAPARAMS. The host SCB index is in SINDEX.
 */
dma_scb:
	mov	A, SINDEX;
	if ((ahc->features & AHC_CMD_CHAN) != 0) {
		mvi	DINDEX, CCHADDR;
		mvi	HSCB_ADDR call set_64byte_addr;
		mov	CCSCBPTR, SCBPTR;
		test	DMAPARAMS, DIRECTION jz dma_scb_tohost;
		mvi	CCHCNT, SCB_64BYTE_SIZE;
		mvi	CCSCBCTL, CCARREN|CCSCBEN|CCSCBDIR|CCSCBRESET;
		cmp	CCSCBCTL, CCSCBDONE|ARRDONE|CCARREN|CCSCBEN|CCSCBDIR jne .;
		jmp	dma_scb_finish;
dma_scb_tohost:
		mvi	CCHCNT, SCB_32BYTE_SIZE;
		if ((ahc->chip & AHC_CHIPID_MASK) == AHC_AIC7895) {
			mvi	CCSCBCTL, CCSCBRESET;
			bmov	CCSCBRAM, SCB_CONTROL, SCB_32BYTE_SIZE;
			or	CCSCBCTL, CCSCBEN|CCSCBRESET;
			test	CCSCBCTL, CCSCBDONE jz .;
		} else {
			mvi	CCSCBCTL, CCARREN|CCSCBEN|CCSCBRESET;
			cmp	CCSCBCTL, CCSCBDONE|ARRDONE|CCARREN|CCSCBEN jne .;
		}
dma_scb_finish:
		clr	CCSCBCTL;
		test	CCSCBCTL, CCARREN|CCSCBEN jnz .;
		ret;
	} else {
		mvi	DINDEX, HADDR;
		mvi	HSCB_ADDR call set_64byte_addr;
		mvi	HCNT[0], SCB_32BYTE_SIZE;
		clr	HCNT[1];
		clr	HCNT[2];
		mov	DFCNTRL, DMAPARAMS;
		test	DMAPARAMS, DIRECTION	jnz dma_scb_fromhost;
		/* Fill it with the SCB data */
copy_scb_tofifo:
		mvi	SINDEX, SCB_CONTROL;
		add	A, SCB_32BYTE_SIZE, SINDEX;
copy_scb_tofifo_loop:
		mov	DFDAT,SINDIR;
		mov	DFDAT,SINDIR;
		mov	DFDAT,SINDIR;
		mov	DFDAT,SINDIR;
		mov	DFDAT,SINDIR;
		mov	DFDAT,SINDIR;
		mov	DFDAT,SINDIR;
		cmp	SINDEX, A jne copy_scb_tofifo_loop;
		or	DFCNTRL, HDMAEN|FIFOFLUSH;
dma_scb_fromhost:
		call	dma_finish;
		/* If we were putting the SCB, we are done */
		test	DMAPARAMS, DIRECTION	jz	return;
		mvi	SCB_CONTROL  call dfdat_in_7;
		call	dfdat_in_7_continued;
		call	dfdat_in_7_continued;
		jmp	dfdat_in_7_continued;
dfdat_in_7:
		mov     DINDEX,SINDEX;
dfdat_in_7_continued:
		mov	DINDIR,DFDAT;
		mov	DINDIR,DFDAT;
		mov	DINDIR,DFDAT;
		mov	DINDIR,DFDAT;
		mov	DINDIR,DFDAT;
		mov	DINDIR,DFDAT;
		mov	DINDIR,DFDAT ret;
	}


/*
 * Wait for DMA from host memory to data FIFO to complete, then disable
 * DMA and wait for it to acknowledge that it's off.
 */
dma_finish:
	test	DFSTATUS,HDONE	jz dma_finish;
	/* Turn off DMA */
	and	DFCNTRL, ~HDMAEN;
	test	DFCNTRL, HDMAEN jnz .;
	ret;

add_scb_to_free_list:
	if ((ahc->flags & AHC_PAGESCBS) != 0) {
		mov	SCB_NEXT, FREE_SCBH;
		mvi	SCB_TAG, SCB_LIST_NULL;
		mov	FREE_SCBH, SCBPTR ret;
	} else {
		mvi	SCB_TAG, SCB_LIST_NULL ret;
	}

if ((ahc->flags & AHC_PAGESCBS) != 0) {
get_free_or_disc_scb:
	cmp	FREE_SCBH, SCB_LIST_NULL jne dequeue_free_scb;
	cmp	DISCONNECTED_SCBH, SCB_LIST_NULL jne dequeue_disc_scb;
return_error:
	mvi	SINDEX, SCB_LIST_NULL	ret;
dequeue_disc_scb:
	mov	SCBPTR, DISCONNECTED_SCBH;
dma_up_scb:
	mvi	DMAPARAMS, FIFORESET;
	mov	SCB_TAG		call dma_scb;
unlink_disc_scb:
	mov	DISCONNECTED_SCBH, SCB_NEXT ret;
dequeue_free_scb:
	mov	SCBPTR, FREE_SCBH;
	mov	FREE_SCBH, SCB_NEXT ret;
}

add_scb_to_disc_list:
/*
 * Link this SCB into the DISCONNECTED list.  This list holds the
 * candidates for paging out an SCB if one is needed for a new command.
 * Modifying the disconnected list is a critical(pause dissabled) section.
 */
	mov	SCB_NEXT, DISCONNECTED_SCBH;
	mov	DISCONNECTED_SCBH, SCBPTR ret;