Hello,
in regards to the buffering effect I observed -- I am hopeful that I have
found a fix:
I have now extended the chars_in_buffer function to return the sum of the
bytes stored in the URB pool awaiting transmission and the bytes in the tx
buffer of the USB-RSA. Now, the tty layer calls the close function of the
driver once all URBs are transferred to USB-RSA AND the USB-RSA emptied its tx
buffer.
The earlier implementation of chars_in_buffer just returned the number of
bytes waiting in the URB pool. The close function would be called once all
URBs were transferred to the USB-RSA. The close function disables the
transmit interrupt of the USB-RSA's serial port. If many data was queued, the
close function would be called before the USB-RSA had finished its
transmission over serial interface. So much for the hard facts.
I think what caused the buffering effect is this: The trailing "0d 0a" was
transferred to the USBRSA's tx buffer, and from there moved to the fifo of
USBRSA's serial port (The fifo is 16 bytes deep. An ST16C550 implements the
serial port). The close function shut off the tx interrupt of the serial port
thereby stopping the transmission on the serial line. The tty layer's next
call to the open function would reenable the tx interrupt, and the remaining
data and with it the trailing "0d 0a" held in the fifo would be sent to the
receiving port.
Here my chars_in_buffer function:
static int usbrsa_chars_in_buffer(struct tty_struct *tty)
{
struct usb_serial_port* port = tty->driver_data;
struct usbrsa_port_private* priv = usb_get_serial_port_data(port);
int chars = 0;
int i = 0;
unsigned long flags;
long t;
int retval;
dbg("%s() port = %d", __func__, port->number);
spin_lock_irqsave(&priv->lock, flags);
//bytes in TX buffer of USBRSA
chars = priv->nofTxMaxBytes - priv->nofTxBytesFree;
// account for URBs in the pool and not yet transferred to the USB-RSA
for (i=0;i<priv->urb_pool_size;i++)
{
if (test_bit(i,&priv->write_urb_pool_lock) != 0)
{
chars +=
priv->write_urb_pool[i]->transfer_buffer_length;
}
}
spin_unlock_irqrestore(&priv->lock, flags);
chars_in_buffer_exit:
dbg("%s(): %d", __func__, chars);
return chars;
}
Cheers Tilman
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