easycap: reset()
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Hi Mike,
Quoted 26 lines · R.M. Thomas
Hi Ezequiel,
As you probably know, I originally developed the driver on the Sourceforge site. Before uploading any new version of the driver I carried out extensive automated testing using various scripts I had written for this purpose. I attach the tarball for the final version of the Sourceforge driver in order to explain what I mean. When you unpack the tarball you will find the script
./tools/checktestPAL.sh, and you will see that this runs the script ./testPAL.sh unattended for 36 test cases.Early versions of the driver did not have the extra
reset()calls, and I found that when I carried out the automated testing with./tools/checktestPAL.shand similar scripts the EasyCAP would sometimes fail to initialize correctly. In these cases no video stream was visible, with mplayer then displaying an unchanging green or black window. On average, I would see this failure in 5-10% of the test cases, but the behavior was not
reproducible: failure would occur randomly on different test cases when I ran./tools/checktestPAL.shagain.I never discovered what caused the failures. I assumed (without any evidence) that one of the EasyCAP chips was prone to latch-up or some similar hardware problem, but I may have been wrong about this. The practical workaround which I found was to forcibly reset the hardware registers whenever the driver detected problems at initialization. This is the reason for the time-consuming repeated use of the function
reset().
Quoted 6 lines
It would certainly be desirable to remove the extra
reset()calls if possible, and I hope you will be able to do so. However, I suggest that driver modifications involvingreset()should be subjected to automated testing, because any resulting problems may not be apparent if testing is limited to one or two cases.
I see. I'll pospone the reset() patch until further testing shows it is stable enough.
Thanks a lot for the test scripts, they'll be of much help.
Quoted 5 lines
On a more general point, I believe the easycap driver would benefit from some radical rewriting. At present it is not integrated with the V4L2 mainstream (for historical reasons), and this needs to be corrected:
That's true. However, the driver works fine and I'm not sure a complete rewrite is a good option.
Quoted 6 lines
Unfortunately I cannot contribute to this myself, not only because I am fully committed now to an entirely different project, but also because I know so little about the V4L2 infrastructure that I could not be of much use. I do hope you will be able to make some progress with it.
I understand. I also hope we make some progress with it :)
If it is at all possible I would like to ask you to send me any information about the driver you have,
I mean datasheets and that sort of stuff.
Thanks a lot for your feedback,
Ezequiel.