UM0851 datasheet(116/245 Pages) STMICROELECTRONICS

116 / 245 page

Communication device drivers

UM0851

116/245

Doc ID 16604 Rev 2

Once the net_device structure has been initialized, the registration process is completed by

passing the structure to register_hdlcdev().

Open HDLC channels

channel_open() is called if the application opens the HDLC channel. It resets the DMA

buffer ring and starts the DMA engine to begin receiving HDLC frames.

Then it calls net_start_queue() to enable transmitting packages.

Finally it calls hdlc_open() to let Generic HDLC Layer finish the device opening.

int channel_open(net_device *dev)

{

struct channel_t *ch = dev_to_hdlc(dev)->priv;

reset_ring(ch);

/* start DMA */

......

net_start_queue(dev);

return hdlc_open(dev);

}

Close HDLC channels

channel_close() is called if the application closes the HDLC channel. It first calls

net_stop_queue() to stop the transmit queue. Then, it writes the STOP command to the

DMA engine and waits for it to be stopped.

Finally it calls hdlc_close() to let the generic HDLC layer finish the device closing.

int channel_close(net_device *dev)

{

struct channel_t *ch = dev_to_hdlc(dev)->priv;

net_stop_queue(dev);

/* stop DMA */

......

/* wait DMA stopped */

......

return hdlc_close(dev);

}

Xmit over HDLC channels

channel_xmit() is called when there is data ready to be sent out. It will append the buffer to

the transmit buffer ring. And if Tx DMA is not running, it will start Tx DMA to transmit the

package. This function is non-blocked. It doesn't wait the transmitting to be completed.

Transmitting status is checked in bottom half of Tx interrupt handler.

int channel_xmit(struct sk_buff *skb, struct net_device *dev)

{

struct channel_t *ch = dev_to_hdlc(dev)->priv;

if (Tx buffer ring full)

return -EBUSY;

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