static void setup_tx_dma(struct pi_local *lp, int length)
{
    unsigned long dma_abs;
    unsigned long flags;
    unsigned long dmachan;

    save_flags(flags);
    cli();

    dmachan = lp->dmachan;
    dma_abs = (unsigned long) (lp->txdmabuf);

    if(!valid_dma_page(dma_abs, DMA_BUFF_SIZE + sizeof(struct mbuf)))
	panic("PI: TX buffer violates DMA boundary!");

    disable_dma(dmachan);
    /* Set DMA mode register to single transfers, incrementing address,
     *  no auto init, reads
     */
    set_dma_mode(dmachan, DMA_MODE_WRITE);
    clear_dma_ff(dmachan);
    set_dma_addr(dmachan, dma_abs);
    /* output byte count */
    set_dma_count(dmachan, length);

    restore_flags(flags);
}

static void handlewrite(struct net_device *dev)
{
	/* called *only* from idle, non-reentrant */
	/* on entry, 0xfb and ltdmabuf holds data */
	int dma = dev->dma;
	int base = dev->base_addr;
	unsigned long flags;
	
	flags=claim_dma_lock();
	disable_dma(dma);
	clear_dma_ff(dma);
	set_dma_mode(dma,DMA_MODE_WRITE);
	set_dma_addr(dma,virt_to_bus(ltdmabuf));
	set_dma_count(dma,800);
	enable_dma(dma);
	release_dma_lock(flags);
	
	inb_p(base+3);
	inb_p(base+2);

	if ( wait_timeout(dev,0xfb) ) {
		flags=claim_dma_lock();
		printk("timed out in handlewrite, dma res %d\n",
			get_dma_residue(dev->dma) );
		release_dma_lock(flags);
	}
}

static __inline__ int 
NCR53c406a_dma_setup (unsigned char *ptr, 
		      unsigned int count, 
		      unsigned char mode) {
    unsigned limit;
    unsigned long flags = 0;
    
    VDEB(printk("dma: before count=%d   ", count));
    if (dma_chan <=3) {
        if (count > 65536)
            count = 65536;
        limit = 65536 - (((unsigned) ptr) & 0xFFFF);
    } else {
        if (count > (65536<<1)) 
            count = (65536<<1);
        limit = (65536<<1) - (((unsigned) ptr) & 0x1FFFF);
    }
    
    if (count > limit) count = limit;
    
    VDEB(printk("after count=%d\n", count));
    if ((count & 1) || (((unsigned) ptr) & 1))
        panic ("NCR53c406a: attempted unaligned DMA transfer\n"); 
    
    flags=claim_dma_lock();
    disable_dma(dma_chan);
    clear_dma_ff(dma_chan);
    set_dma_addr(dma_chan, (long) ptr);
    set_dma_count(dma_chan, count);
    set_dma_mode(dma_chan, mode);
    enable_dma(dma_chan);
    release_dma_lock(flags);    
    
    return count;
}

static void setup_DMA(void) {

	unsigned long addr,count;
	unsigned char dma_code;
	dma_code = DMA_WRITE;
	if (command == FD_READ)
		dma_code = DMA_READ;
	if (command == FD_FORMAT) {
		addr = (long) tmp_floppy_area;
		count = floppy->sect*4;
	} else {
		addr = (long) CURRENT->buffer;
		count = 1024;
	}
	if (read_track) {
/* mark buffer-track bad, in case all this fails.. */
		buffer_drive = buffer_track = -1;
		count = floppy->sect*floppy->head*512;
		addr = (long) floppy_track_buffer;
	} else if (addr >= LAST_DMA_ADDR) {
		addr = (long) tmp_floppy_area;
		if (command == FD_WRITE)
			copy_buffer(CURRENT->buffer, tmp_floppy_area);
	}
	cli();
	disable_dma(FLOPPY_DMA);

	//clear_dma_ff(FLOPPY_DMA);
	set_dma_mode(FLOPPY_DMA, (command == FD_READ)? DMA_MODE_READ : DMA_MODE_WRITE);
	set_dma_addr(FLOPPY_DMA, addr);
	set_dma_count(FLOPPY_DMA, count);
	enable_dma(FLOPPY_DMA);
	sti();
}

static void receive_packet(struct net_device *dev, int len)
{
	int rlen;
	elp_device *adapter = dev->priv;
	void *target;
	struct sk_buff *skb;
	unsigned long flags;

	rlen = (len + 1) & ~1;
	skb = dev_alloc_skb(rlen + 2);

	if (!skb) {
		printk(KERN_WARNING "%s: memory squeeze, dropping packet\n", dev->name);
		target = adapter->dma_buffer;
		adapter->current_dma.target = NULL;
		/* FIXME: stats */
		return;
	}

	skb_reserve(skb, 2);
	target = skb_put(skb, rlen);
	if ((unsigned long)(target + rlen) >= MAX_DMA_ADDRESS) {
		adapter->current_dma.target = target;
		target = adapter->dma_buffer;
	} else {
		adapter->current_dma.target = NULL;
	}

	/* if this happens, we die */
	if (test_and_set_bit(0, (void *) &adapter->dmaing))
		printk(KERN_ERR "%s: rx blocked, DMA in progress, dir %d\n", dev->name, adapter->current_dma.direction);

	skb->dev = dev;
	adapter->current_dma.direction = 0;
	adapter->current_dma.length = rlen;
	adapter->current_dma.skb = skb;
	adapter->current_dma.start_time = jiffies;

	outb_control(adapter->hcr_val | DIR | TCEN | DMAE, dev);

	flags=claim_dma_lock();
	disable_dma(dev->dma);
	clear_dma_ff(dev->dma);
	set_dma_mode(dev->dma, 0x04);	/* dma read */
	set_dma_addr(dev->dma, isa_virt_to_bus(target));
	set_dma_count(dev->dma, rlen);
	enable_dma(dev->dma);
	release_dma_lock(flags);

	if (elp_debug >= 3) {
		printk(KERN_DEBUG "%s: rx DMA transfer started\n", dev->name);
	}

	if (adapter->rx_active)
		adapter->rx_active--;

	if (!adapter->busy)
		printk(KERN_WARNING "%s: receive_packet called, busy not set.\n", dev->name);
}

static netdev_tx_t send_packet(struct net_device *dev, struct sk_buff *skb)
{
	elp_device *adapter = netdev_priv(dev);
	unsigned long target;
	unsigned long flags;

	unsigned int nlen = (((skb->len < 60) ? 60 : skb->len) + 1) & (~1);

	if (test_and_set_bit(0, (void *) &adapter->busy)) {
		if (elp_debug >= 2)
			pr_debug("%s: transmit blocked\n", dev->name);
		return false;
	}

	dev->stats.tx_bytes += nlen;

	adapter->tx_pcb.command = CMD_TRANSMIT_PACKET;
	adapter->tx_pcb.length = sizeof(struct Xmit_pkt);
	adapter->tx_pcb.data.xmit_pkt.buf_ofs
	    = adapter->tx_pcb.data.xmit_pkt.buf_seg = 0;	
	adapter->tx_pcb.data.xmit_pkt.pkt_len = nlen;

	if (!send_pcb(dev, &adapter->tx_pcb)) {
		adapter->busy = 0;
		return false;
	}
	
	if (test_and_set_bit(0, (void *) &adapter->dmaing))
		pr_debug("%s: tx: DMA %d in progress\n", dev->name, adapter->current_dma.direction);

	adapter->current_dma.direction = 1;
	adapter->current_dma.start_time = jiffies;

	if ((unsigned long)(skb->data + nlen) >= MAX_DMA_ADDRESS || nlen != skb->len) {
		skb_copy_from_linear_data(skb, adapter->dma_buffer, nlen);
		memset(adapter->dma_buffer+skb->len, 0, nlen-skb->len);
		target = isa_virt_to_bus(adapter->dma_buffer);
	}
	else {
		target = isa_virt_to_bus(skb->data);
	}
	adapter->current_dma.skb = skb;

	flags=claim_dma_lock();
	disable_dma(dev->dma);
	clear_dma_ff(dev->dma);
	set_dma_mode(dev->dma, 0x48);	
	set_dma_addr(dev->dma, target);
	set_dma_count(dev->dma, nlen);
	outb_control(adapter->hcr_val | DMAE | TCEN, dev);
	enable_dma(dev->dma);
	release_dma_lock(flags);

	if (elp_debug >= 3)
		pr_debug("%s: DMA transfer started\n", dev->name);

	return true;
}

static ssize_t __dma_write(gpib_board_t *board, nec7210_private_t *priv, dma_addr_t address, size_t length)
{
	unsigned long flags, dma_irq_flags;
	int residue = 0;
	int retval = 0;

	spin_lock_irqsave(&board->spinlock, flags);

	/* program dma controller */
	dma_irq_flags = claim_dma_lock();
	disable_dma(priv->dma_channel);
	clear_dma_ff(priv->dma_channel);
	set_dma_count(priv->dma_channel, length);
	set_dma_addr(priv->dma_channel, address);
	set_dma_mode(priv->dma_channel, DMA_MODE_WRITE );
	enable_dma(priv->dma_channel);
	release_dma_lock(dma_irq_flags);

	// enable board's dma for output
	nec7210_set_reg_bits( priv, IMR2, HR_DMAO, HR_DMAO );

	clear_bit(WRITE_READY_BN, &priv->state);
	set_bit(DMA_WRITE_IN_PROGRESS_BN, &priv->state);

	spin_unlock_irqrestore(&board->spinlock, flags);

	// suspend until message is sent
	if(wait_event_interruptible(board->wait, test_bit(DMA_WRITE_IN_PROGRESS_BN, &priv->state) == 0 ||
		test_bit( BUS_ERROR_BN, &priv->state ) || test_bit( DEV_CLEAR_BN, &priv->state ) ||
		test_bit(TIMO_NUM, &board->status)))
	{
		GPIB_DPRINTK( "gpib write interrupted!\n" );
		retval = -ERESTARTSYS;
	}
	if(test_bit(TIMO_NUM, &board->status))
		retval = -ETIMEDOUT;
	if( test_and_clear_bit( DEV_CLEAR_BN, &priv->state ) )
		retval = -EINTR;
	if( test_and_clear_bit( BUS_ERROR_BN, &priv->state ) )
		retval = -EIO;

	// disable board's dma
	nec7210_set_reg_bits( priv, IMR2, HR_DMAO, 0 );

	dma_irq_flags = claim_dma_lock();
	clear_dma_ff(priv->dma_channel);
	disable_dma(priv->dma_channel);
	residue = get_dma_residue(priv->dma_channel);
	release_dma_lock( dma_irq_flags );

	if(residue)
		retval = -EPIPE;

	return retval ? retval : length;
}

void labpc_drain_dma(struct comedi_device *dev)
{
	struct labpc_private *devpriv = dev->private;
	struct comedi_subdevice *s = dev->read_subdev;
	struct comedi_async *async = s->async;
	struct comedi_cmd *cmd = &async->cmd;
	int status;
	unsigned long flags;
	unsigned int max_points, num_points, residue, leftover;
	int i;

	status = devpriv->stat1;

	flags = claim_dma_lock();
	disable_dma(devpriv->dma_chan);
	/* clear flip-flop to make sure 2-byte registers for
	 * count and address get set correctly */
	clear_dma_ff(devpriv->dma_chan);

	/* figure out how many points to read */
	max_points = devpriv->dma_transfer_size / sample_size;
	/* residue is the number of points left to be done on the dma
	 * transfer.  It should always be zero at this point unless
	 * the stop_src is set to external triggering.
	 */
	residue = get_dma_residue(devpriv->dma_chan) / sample_size;
	num_points = max_points - residue;
	if (cmd->stop_src == TRIG_COUNT && devpriv->count < num_points)
		num_points = devpriv->count;

	/* figure out how many points will be stored next time */
	leftover = 0;
	if (cmd->stop_src != TRIG_COUNT) {
		leftover = devpriv->dma_transfer_size / sample_size;
	} else if (devpriv->count > num_points) {
		leftover = devpriv->count - num_points;
		if (leftover > max_points)
			leftover = max_points;
	}

	/* write data to comedi buffer */
	for (i = 0; i < num_points; i++)
		cfc_write_to_buffer(s, devpriv->dma_buffer[i]);

	if (cmd->stop_src == TRIG_COUNT)
		devpriv->count -= num_points;

	/* set address and count for next transfer */
	set_dma_addr(devpriv->dma_chan, devpriv->dma_addr);
	set_dma_count(devpriv->dma_chan, leftover * sample_size);
	release_dma_lock(flags);

	async->events |= COMEDI_CB_BLOCK;
}

static int sscape_start_dma(int chan, unsigned long physaddr, int count, int dma_mode)
{
	unsigned long flags;

	flags = claim_dma_lock();
	disable_dma(chan);
	clear_dma_ff(chan);
	set_dma_mode(chan, dma_mode);
	set_dma_addr(chan, physaddr);
	set_dma_count(chan, count);
	enable_dma(chan);
	release_dma_lock(flags);
	return 0;
}

void dac0800_startdma(unsigned char *buf, unsigned int size)
{
	/* Clear DMA interrupt */
	disable_dma(DAC0800_DMA_CHAN);

	/* Do DMA write to i/o operation */
	set_dma_mode(DAC0800_DMA_CHAN, DMA_MODE_WRITE);
	set_dma_device_addr(DAC0800_DMA_CHAN, DAC0800_DMA_DESTADDR);
	set_dma_addr(DAC0800_DMA_CHAN, (unsigned int) buf);
	set_dma_count(DAC0800_DMA_CHAN, size);

	/* Fire it off! */
	enable_dma(DAC0800_DMA_CHAN);
}

/**
 * snd_dma_program - program an ISA DMA transfer
 * @dma: the dma number
 * @addr: the physical address of the buffer
 * @size: the DMA transfer size
 * @mode: the DMA transfer mode, DMA_MODE_XXX
 *
 * Programs an ISA DMA transfer for the given buffer.
 */
void snd_dma_program(unsigned long dma,
		     unsigned long addr, unsigned int size,
                     unsigned short mode)
{
	unsigned long flags;

	flags = claim_dma_lock();
	disable_dma(dma);
	clear_dma_ff(dma);
	set_dma_mode(dma, mode);
	set_dma_addr(dma, addr);
	set_dma_count(dma, size);
	if (!(mode & DMA_MODE_NO_ENABLE))
		enable_dma(dma);
	release_dma_lock(flags);
}

static void setup_rx_dma(struct pt_local *lp)
{
	unsigned long flags;
	int cmd;
	unsigned long dma_abs;
	unsigned char dmachan;

	save_flags(flags);
	cli();

	dma_abs = (unsigned long) (lp->rcvbuf->data);
	dmachan = lp->dmachan;
	cmd = lp->base + CTL;

	if(!valid_dma_page(dma_abs, DMA_BUFF_SIZE + sizeof(struct mbuf)))
		panic("PI: RX buffer violates DMA boundary!");

	/* Get ready for RX DMA */
	wrtscc(lp->cardbase, cmd, R1, WT_FN_RDYFN | WT_RDY_RT | INT_ERR_Rx | EXT_INT_ENAB);

	disable_dma(dmachan);
	clear_dma_ff(dmachan);

	/*
	 *	Set DMA mode register to single transfers, incrementing address,
	 *	auto init, writes
	 */

	set_dma_mode(dmachan, DMA_MODE_READ | 0x10);
	set_dma_addr(dmachan, dma_abs);
	set_dma_count(dmachan, lp->bufsiz);
	enable_dma(dmachan);

	/*
	 *	If a packet is already coming in, this line is supposed to
	 *	avoid receiving a partial packet.
	 */

	wrtscc(lp->cardbase, cmd, R0, RES_Rx_CRC);

	/* Enable RX dma */
	wrtscc(lp->cardbase, cmd, R1,
		WT_RDY_ENAB | WT_FN_RDYFN | WT_RDY_RT | INT_ERR_Rx | EXT_INT_ENAB);

	restore_flags(flags);
}

static int sound_start_dma(struct dma_buffparms *dmap, unsigned long physaddr, int count, int dma_mode)
{
	unsigned long flags;
	int chan = dmap->dma;

	/* printk( "Start DMA%d %d, %d\n",  chan,  (int)(physaddr-dmap->raw_buf_phys),  count); */

	flags = claim_dma_lock();
	disable_dma(chan);
	clear_dma_ff(chan);
	set_dma_mode(chan, dma_mode);
	set_dma_addr(chan, physaddr);
	set_dma_count(chan, count);
	enable_dma(chan);
	release_dma_lock(flags);

	return 0;
}

static void handlecommand(struct net_device *dev)
{
	/* on entry, 0xfa and ltdmacbuf holds command */
	int dma = dev->dma;
	int base = dev->base_addr;
	unsigned long flags;

	flags=claim_dma_lock();
	disable_dma(dma);
	clear_dma_ff(dma);
	set_dma_mode(dma,DMA_MODE_WRITE);
	set_dma_addr(dma,virt_to_bus(ltdmacbuf));
	set_dma_count(dma,50);
	enable_dma(dma);
	release_dma_lock(flags);
	inb_p(base+3);
	inb_p(base+2);
	if ( wait_timeout(dev,0xfa) ) printk("timed out in handlecommand\n");
} 

static void i8237A_resume(void)
{
	unsigned long flags;
	int i;

	flags = claim_dma_lock();

	dma_outb(0, DMA1_RESET_REG);
	dma_outb(0, DMA2_RESET_REG);

	for (i = 0; i < 8; i++) {
		set_dma_addr(i, 0x000000);
		
		set_dma_count(i, 1);
	}

	
	enable_dma(4);

	release_dma_lock(flags);
}

/* read data from the card */
static void handlefd(struct net_device *dev)
{
	int dma = dev->dma;
	int base = dev->base_addr;
	unsigned long flags;

	flags=claim_dma_lock();
	disable_dma(dma);
	clear_dma_ff(dma);
	set_dma_mode(dma,DMA_MODE_READ);
	set_dma_addr(dma,virt_to_bus(ltdmabuf));
	set_dma_count(dma,800);
	enable_dma(dma);
	release_dma_lock(flags);

	inb_p(base+3);
	inb_p(base+2);

	if ( wait_timeout(dev,0xfd) ) printk("timed out in handlefd\n");
	sendup_buffer(dev);
} 

/* read a command from the card */
static void handlefc(struct net_device *dev)
{
	/* called *only* from idle, non-reentrant */
	int dma = dev->dma;
	int base = dev->base_addr;
	unsigned long flags;


	flags=claim_dma_lock();
	disable_dma(dma);
	clear_dma_ff(dma);
	set_dma_mode(dma,DMA_MODE_READ);
	set_dma_addr(dma,virt_to_bus(ltdmacbuf));
	set_dma_count(dma,50);
	enable_dma(dma);
	release_dma_lock(flags);

	inb_p(base+3);
	inb_p(base+2);

	if ( wait_timeout(dev,0xfc) ) printk("timed out in handlefc\n");
}

void labpc_setup_dma(struct comedi_device *dev, struct comedi_subdevice *s)
{
	struct labpc_private *devpriv = dev->private;
	struct comedi_cmd *cmd = &s->async->cmd;
	unsigned long irq_flags;

	irq_flags = claim_dma_lock();
	disable_dma(devpriv->dma_chan);
	/* clear flip-flop to make sure 2-byte registers for
	 * count and address get set correctly */
	clear_dma_ff(devpriv->dma_chan);
	set_dma_addr(devpriv->dma_chan, devpriv->dma_addr);
	/* set appropriate size of transfer */
	devpriv->dma_transfer_size = labpc_suggest_transfer_size(cmd);
	if (cmd->stop_src == TRIG_COUNT &&
	    devpriv->count * sample_size < devpriv->dma_transfer_size)
		devpriv->dma_transfer_size = devpriv->count * sample_size;
	set_dma_count(devpriv->dma_chan, devpriv->dma_transfer_size);
	enable_dma(devpriv->dma_chan);
	release_dma_lock(irq_flags);
	/* set CMD3 bits for caller to enable DMA and interrupt */
	devpriv->cmd3 |= (CMD3_DMAEN | CMD3_DMATCINTEN);
}

static int send_packet(struct net_device *dev, struct sk_buff *skb)
{
	elp_device *adapter = dev->priv;
	unsigned long target;
	unsigned long flags;

	/*
	 * make sure the length is even and no shorter than 60 bytes
	 */
	unsigned int nlen = (((skb->len < 60) ? 60 : skb->len) + 1) & (~1);

	if (test_and_set_bit(0, (void *) &adapter->busy)) {
		if (elp_debug >= 2)
			printk(KERN_DEBUG "%s: transmit blocked\n", dev->name);
		return FALSE;
	}

	adapter->stats.tx_bytes += nlen;

	/*
	 * send the adapter a transmit packet command. Ignore segment and offset
	 * and make sure the length is even
	 */
	adapter->tx_pcb.command = CMD_TRANSMIT_PACKET;
	adapter->tx_pcb.length = sizeof(struct Xmit_pkt);
	adapter->tx_pcb.data.xmit_pkt.buf_ofs
	    = adapter->tx_pcb.data.xmit_pkt.buf_seg = 0;	/* Unused */
	adapter->tx_pcb.data.xmit_pkt.pkt_len = nlen;

	if (!send_pcb(dev, &adapter->tx_pcb)) {
		adapter->busy = 0;
		return FALSE;
	}
	/* if this happens, we die */
	if (test_and_set_bit(0, (void *) &adapter->dmaing))
		printk(KERN_DEBUG "%s: tx: DMA %d in progress\n", dev->name, adapter->current_dma.direction);

	adapter->current_dma.direction = 1;
	adapter->current_dma.start_time = jiffies;

	if ((unsigned long)(skb->data + nlen) >= MAX_DMA_ADDRESS || nlen != skb->len) {
		skb_copy_from_linear_data(skb, adapter->dma_buffer, nlen);
		memset(adapter->dma_buffer+skb->len, 0, nlen-skb->len);
		target = isa_virt_to_bus(adapter->dma_buffer);
	}
	else {
		target = isa_virt_to_bus(skb->data);
	}
	adapter->current_dma.skb = skb;

	flags=claim_dma_lock();
	disable_dma(dev->dma);
	clear_dma_ff(dev->dma);
	set_dma_mode(dev->dma, 0x48);	/* dma memory -> io */
	set_dma_addr(dev->dma, target);
	set_dma_count(dev->dma, nlen);
	outb_control(adapter->hcr_val | DMAE | TCEN, dev);
	enable_dma(dev->dma);
	release_dma_lock(flags);

	if (elp_debug >= 3)
		printk(KERN_DEBUG "%s: DMA transfer started\n", dev->name);

	return TRUE;
}

//.........这里部分代码省略.........
	inb_p(io+5);
	inb_p(io+5); /* enable dma */
	inb_p(io+6); /* tri-state interrupt line */

	ssleep(1);
	
	/* now, figure out which dma channel we're using, unless it's
	   already been specified */
	/* well, 0 is a legal DMA channel, but the LTPC card doesn't
	   use it... */
	dma = ltpc_probe_dma(io, dma);
	if (!dma) {  /* no dma channel */
		printk(KERN_ERR "No DMA channel found on ltpc card.\n");
		err = -ENODEV;
		goto out3;
	}

	/* print out friendly message */
	if(irq)
		printk(KERN_INFO "Apple/Farallon LocalTalk-PC card at %03x, IR%d, DMA%d.\n",io,irq,dma);
	else
		printk(KERN_INFO "Apple/Farallon LocalTalk-PC card at %03x, DMA%d.  Using polled mode.\n",io,dma);

	/* Fill in the fields of the device structure with ethernet-generic values. */
	dev->hard_start_xmit = ltpc_xmit;
	dev->hard_header = ltpc_hard_header;
	dev->get_stats = ltpc_get_stats;

	/* add the ltpc-specific things */
	dev->do_ioctl = &ltpc_ioctl;

	dev->set_multicast_list = &set_multicast_list;
	dev->mc_list = NULL;
	dev->base_addr = io;
	dev->irq = irq;
	dev->dma = dma;

	/* the card will want to send a result at this point */
	/* (I think... leaving out this part makes the kernel crash,
           so I put it back in...) */

	f=claim_dma_lock();
	disable_dma(dma);
	clear_dma_ff(dma);
	set_dma_mode(dma,DMA_MODE_READ);
	set_dma_addr(dma,virt_to_bus(ltdmabuf));
	set_dma_count(dma,0x100);
	enable_dma(dma);
	release_dma_lock(f);

	(void) inb_p(io+3);
	(void) inb_p(io+2);
	timeout = jiffies+100*HZ/100;

	while(time_before(jiffies, timeout)) {
		if( 0xf9 == inb_p(io+6))
			break;
		schedule();
	}

	if(debug & DEBUG_VERBOSE) {
		printk("setting up timer and irq\n");
	}

	/* grab it and don't let go :-) */
	if (irq && request_irq( irq, &ltpc_interrupt, 0, "ltpc", dev) >= 0)
	{
		(void) inb_p(io+7);  /* enable interrupts from board */
		(void) inb_p(io+7);  /* and reset irq line */
	} else {
		if( irq )
			printk(KERN_ERR "ltpc: IRQ already in use, using polled mode.\n");
		dev->irq = 0;
		/* polled mode -- 20 times per second */
		/* this is really, really slow... should it poll more often? */
		init_timer(&ltpc_timer);
		ltpc_timer.function=ltpc_poll;
		ltpc_timer.data = (unsigned long) dev;

		ltpc_timer.expires = jiffies + HZ/20;
		add_timer(&ltpc_timer);
	}
	err = register_netdev(dev);
	if (err)
		goto out4;

	return NULL;
out4:
	del_timer_sync(&ltpc_timer);
	if (dev->irq)
		free_irq(dev->irq, dev);
out3:
	free_pages((unsigned long)ltdmabuf, get_order(1000));
out2:
	release_region(io, 8);
out1:
	free_netdev(dev);
out:
	return ERR_PTR(err);
}