On 18-Nov-2002 Mark McClelland wrote:
> Duncan Haldane wrote:
>
> >If two cameras are registered, one on /dev/video0 and one on /dev/video1,
> >and I use e.g. xawtv or gqcam to monitor them, I cannot open /dev/video1
> >when /dev/video0 is open and vice-versa. This happens for two cpia
> >devices and one cpia + one ov511 device.
>
> That's because both cameras are trying to use nearly all of the USB's
> bandwidth. Or, more precisely, each is trying to schedule an ISO packet
Yes, this seems correct: I have now traced the problem to disruption of
communication of commands to/from the cpia cam (ReadPacket() in cpia_usb.c/
cpia_usb_transferCmd()). This eventually causes de/re-registration of
the camera, leaving a frozen viewer window that needs a reboot to clear
it.... (incomplete cleanup ?) -- nasty.
Is there any kind of locking that cpia_usb_transferCmd could use to
temporarily grab the full usb bandwidth for camera control (so this takes
precedence over data transfer by other devices?) At the very least I would
hope to prevent hanging that requires a reboot!.
static int ReadPacket(struct usb_device *udev, u8 *packet, u8 *buf, size_t size)
{
if (!packet || size <= 0)
return -EINVAL;
return usb_control_msg(udev, usb_rcvctrlpipe(udev, 0),
packet[1] + (packet[0] << 8),
USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
packet[2] + (packet[3] << 8),
packet[4] + (packet[5] << 8), buf, size, HZ);
}
static int cpia_usb_transferCmd(void *privdata, u8 *command, u8 *data)
{
int err = 0;
<snip>
struct usb_device *udev = ucpia->dev;
u8 buffer[8];
<snip>
err = ReadPacket(udev, command, buffer, 8);
if (err < 0)
return err;
<snip>
}
<snip>
> Check the descriptors. As long as there's an alternate setting where
> MxPS <= 1023 / 2 then you should be in business. You can either have the
> packet size or alternate number be a module param, or you can do a
> "cams" thing like ov511. Or, you can allow the frame rate to be set
> somewhere, and have the driver automatically choose the minimum possible
> packet size that can still sustain that frame rate.
Mark, I attach a bzipped copy of cpia_usb.c, could you cast your experienced
eye over it to see where a setting like this could be controlled, and point
me at it? I gather that your ov511 code originally derived somewhat from
cpia driver code, maybe you can recognize something?
Duncan
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E-Mail: Duncan Haldane <f.duncan.m.haldane@xxxxxxxxxxxxxxxx>
Date: 18-Nov-2002
Time: 11:20:10
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