Hi
For a project I'm working on we had to add GPIO support to the cp2103 driver in
the 2.6.20.4 kernel. We are controlling a GPIO via ictl to flash an LED. We'd
like to hit something along the lines or 1-3HZ. So nothing too fast. I use a
control URB to tell the cp2103 device to toggle its GPIO state. My function like:
static void cp2103_send_GPIO_packet(struct usb_serial_port *port, u8 mask, u8
latch){
int i,ret_val;
unsigned long flags;
u8 pkt[USB_GPIO_PKT_SIZE]={0x40,0xff,0xe1,0x37,0x0f,0x00,0x00,0x00};
spin_lock_bh(&port->lock);
if (port->write_urb_busy) {
spin_unlock_bh(&port->lock);
dbg("%s - already writing", __FUNCTION__);
return 0;
}
port->write_urb_busy = 1;
spin_unlock_bh(&port->lock);
/* place the latch and mask bytes in the correct place in the packet */
pkt[4] = latch;
pkt[5] = mask;
if(port->write_urb->setup_packet == NULL){
port->write_urb->setup_packet = kmalloc(sizeof(u8)*USB_GPIO_PKT_SIZE,
GFP_KERNEL);
memcpy(port->write_urb->setup_packet, pkt, USB_GPIO_PKT_SIZE);
/* Fill our Control Packet */
usb_fill_control_urb(port->write_urb, port->serial->dev,
usb_sndctrlpipe(port->serial->dev, 0),
port->write_urb->setup_packet,
port->write_urb->transfer_buffer,
0, cp2103_send_GPIO_callback, port);
ret_val = usb_submit_urb(port->write_urb, GFP_ATOMIC);
if(ret_val){
printk("[ERROR: usb_submit_urb:%i]\n",ret_val);
}
}else{
printk("[ERROR: port->write_urb->setup_packet is NOT NULL\n");
port->write_urb_busy=0;
}
}
In kernel userland I have a loop that runs every 500ms at the moment toggling
the state of the GPIO. I have verified that the loop is running fairly close to
500ms (within 10% no issues), and looked at debug code from kernel space and the
ioctl function is being run at the same rate. The ioctl always returns success
to the user application, but the LED flashes at a strange rate. It doesn't
appear to toggle every ioctl call. If I call the ioctl function several times
in a row suddenly it flashes every 500ms no problem.
This leads me to my question. Is there a buffer that the control URB ends up
sitting in that doesn't get flushed until a certain number of bytes are sent to
the USB end point? If this is the case, is there an accepted method of fushing
the URB to the USB endpoint?
I'm not too familiar with the USB system of Linux at this point. Trying to
familiarize myself with it while trying to meet my deadlines of getting this
software functioning the way my bosses want.
Thanks
Andrew McKay
Iders Inc.
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