[Linux-uvc-devel] PATCH: Acer Crystal Eye WebCam (064e:a101 Suyin Corp.)

[Michael S. <spa...@gm...>]

Hi,


I've got an Acer laptop with a Crystal Eye WebCam which identifies as follows:

Bus 003 Device 002: ID 064e:a101 Suyin Corp.

This is listed as a supported device here:
http://linux-uvc.berlios.de/#devices

But in practice using the current subversion checkout:

URL: svn://svn.berlios.de/linux-uvc/linux-uvc/trunk
Repository Root: svn://svn.berlios.de/linux-uvc
Repository UUID: 790547d8-3c09-0410-a358-857946b093de
Revision: 212
Node Kind: directory
Schedule: normal
Last Changed Author: pinchartl
Last Changed Rev: 212
Last Changed Date: 2008-05-29 15:56:11 +0100 (Thu, 29 May 2008)

When compiled and running (say), luvcview, I get this error:
~/Incoming> luvcview
luvcview 0.2.4

[snip]
Unable to start capture: Protocol error
Error grabbing
Cleanup done. Exiting ...

I get similar errors from other software (eg opencv, python v4l2 bindings, etc):
~/Incoming> ./WebCam.py
Traceback (most recent call last):
  File "./WebCam.py", line 238, in <module>
    VideoCaptureSource(fps=32),
  File "./WebCam.py", line 139, in __init__
    self.camera.start()
EnvironmentError: ioctl(VIDIOC_STREAMON) failure : 71, Protocol error

It turns out that, for whatever reason, when the above error occurs,
it switches on the webcam. (a little green light comes on). Rerunning
results in the program then normally working (but green light goes out
on exit, etc). Then failing when rerun again (leaving light on), etc.

Anyway, I hunted down the problem - the "Protocol Error" is actually
caused by this line:
uvc_video.c

               if ((ret = usb_set_interface(video->dev->udev, intfnum, i)) < 0)
                       return ret;

So it's *something* to do with the device presumably not always being
switched "on" I guess. How that is supposed to be done, I don't know.

HOWEVER, I have made a patch to uvc_video.c that works:

~/linux-uvc> svn diff
Index: uvc_video.c
===================================================================
--- uvc_video.c (revision 212)
+++ uvc_video.c (working copy)
@@ -750,8 +750,13 @@
                if (i >= intf->num_altsetting)
                        return -EIO;

-               if ((ret = usb_set_interface(video->dev->udev, intfnum, i)) < 0)
-                       return ret;
+               if ((ret = usb_set_interface(video->dev->udev,
intfnum, i)) < 0) {
+                       if (ret == -71) { // If we get this error,
give it another go & retry
+                               if ((ret =
usb_set_interface(video->dev->udev, intfnum, i)) < 0)
+                                       return ret;
+                       } else
+                               return ret;
+               }

                ret = uvc_init_video_isoc(video, ep);
        } else {

You'll note that I just blindly give the same call another go. The
first one manages to
switch the green light on, the second causes it to be useful/usable.

This rather surprisingly worked, and so this has fixed this issue with
this webcam as used by the following software:
   * pygame.camera
   * opencv
   * luvcview
   * Skype

If this isn't the "correct" way of doing this,please let me know what
to test and I'll try a
different patch :-)

BTW, many thanks for writing this module - it's great/really useful :-)

Regards,


Michael.