> On Fri, 2008-07-25 at 00:36 +0200, Luc Janssen wrote: >> Hello all, >> >> I recently upgraded my MythTV box to Mythdora 5.0 hoping to resolve some >> problems I had in using MythTV. Many problems have disappeared, >> however... >> at least one remained. >> >> When I select a TV-channel normally everything works fine, but sometimes >> the capture appears in black and white. When I change the channel and >> then >> return to the "black-white" channel, very often this channel reappears >> in >> full colour! >> >> The same can happen when the mythtv box records a television program. >> The >> captured video often is in black-white while at other times the capture >> for the same channel appears in colour. > > You likely have a chroma subcarrier locking problem. This is more > likely to happen with weak or noisy signals. > > Taking steps to improve signal quality may make the problem go away: > > http://www.ivtvdriver.org/index.php/Howto:Improve_signal_quality > The suggestion the signal is weak was my first starting point to find a solution. I tried to connect the mythtv-box closer to the signal coming into my house (so shorter cables). It did not seem to help :-(
However, the fact that certain (quite many to be honest) channels sometimes produced B/W and your remark of weak and noisy signal, gave me the impression that the tuning of the PVR-500 capture card was suboptimal. I therefore started to play with the frequencies in mythtv by giving commandline SQL-commands to the channel table in mythconverg. The problem is that the frequencies given by the cable companies are given in channel number representation in stead of Hz, so a proper comparison is not possible for me because I do not know the exact conversion rules from channel number representation to Hz. Nevertheless I chose three channels of which I knew I had sometimes B/W recordings and changed the frequencies a little bit (shifts of around 250 kHz) and started recording as many programs as possible on these channels. After some tweaking all recordings were in colour. Now, a few days later I can say all recordings so far are in colour: no B/W capturing has taken place. Preliminary conclusion: It seems that the automatic tuning of the capture card to obtain the proper frequencies does not work properly for all channels. It seems to be solved now, thanks to the remark about bad signal quality. > Or, if you prefer a possible software solution, then find this line in > linux/drivers/media/video/cx25840/cx25840-core.c:cx25840_initialize() > > cx25840_and_or(client, 0x401, ~0x18, 0); > > and change it to > > cx25840_and_or(client, 0x401, ~0x18, 0x10); > > And recompile and reinstall at least the cx25840 module. Then unload > the ivtv and cx25840 modules and reload the ivtv module. > As you can imagine, this step seems not to be necessary. Anyway, thanks for the suggestions. They took me further in my search for a solution. Kind regards, Luc > It looks like the cx25840 module currently sets the CX25843 chroma > subcarrier locking to "Manual lock rate, slow locking" (Which one should > only really do when also implementing fast rate locking on channel > switching - ivtv doesn't). The suggested change will set chroma > subcarrier locking to "Auto lock rate". > > Auto lock rate uses a fast chroma subcarrier locking mechanism when you > don't have chroma subcarrier lock, and a slow chroma subcarrier locking > algorithm when you do have chroma subcarrier lock (to avoid pulling out > of lock easily due to noise). > > See section 3.4.13 of the CX25840/1/2/3 data sheet at > > http://dl.ivtvdriver.org/datasheets/video/cx25840.pdf > > if you want more details. Note that the CSC_LOCK bit (0x08) of register > 0x40e can be used to determine if you actually have chroma subcarrier > lock or not at any given time. With some effort on the command line, > v4l2-dbg can be used to inspect the cx2584x registers at any time. > > Regards, > Andy > > >> A few remarks: >> - Without being sure I suspect this problem appears only at a few >> TV-channels, i.e. this problem is not present for each TV-channel I >> have. >> - I had this problem with my previous version of mythtv (0.20). I do not >> know what version of ivtv was used. >> - In the log file /var/log/mythtv/mythbackend.log I can not see any >> difference in logging information whether the capturing is in colour or >> B/W. >> >> Info: >> - MythDora 5.0 >> - MythTV 0.21-191.fc8 >> - IVTV 1.0.3-136.fc8 >> - ivtv-firmware 20070217-17 >> - dmesg | grep -i ivtv: >> ivtv: Start initialization, version 1.2.0 >> ivtv0: Initializing card #0 >> ivtv0: Autodetected Hauppauge card (cx23416 based) >> ivtv0: Unreasonably low latency timer, setting to 64 (was 32) >> ivtv0: Autodetected WinTV PVR 500 (unit #1) >> cx25840 1-0044: cx25843-24 found @ 0x88 (ivtv i2c driver #0) >> tuner 1-0060: chip found @ 0xc0 (ivtv i2c driver #0) >> tuner 1-0043: chip found @ 0x86 (ivtv i2c driver #0) >> tuner 1-0061: chip found @ 0xc2 (ivtv i2c driver #0) >> wm8775 1-001b: chip found @ 0x36 (ivtv i2c driver #0) >> ivtv0: Registered device video0 for encoder MPG (4096 kB) >> ivtv0: Registered device video32 for encoder YUV (2048 kB) >> ivtv0: Registered device vbi0 for encoder VBI (1024 kB) >> ivtv0: Registered device video24 for encoder PCM (320 kB) >> ivtv0: Registered device radio0 for encoder radio >> ivtv0: Initialized card #0: WinTV PVR 500 (unit #1) >> ivtv1: Initializing card #1 >> ivtv1: Autodetected Hauppauge card (cx23416 based) >> ivtv1: Unreasonably low latency timer, setting to 64 (was 32) >> ivtv1: Correcting tveeprom data: no radio present on second unit >> ivtv1: Autodetected WinTV PVR 500 (unit #2) >> cx25840 2-0044: cx25843-24 found @ 0x88 (ivtv i2c driver #1) >> tuner 2-0043: chip found @ 0x86 (ivtv i2c driver #1) >> tuner 2-0061: chip found @ 0xc2 (ivtv i2c driver #1) >> wm8775 2-001b: chip found @ 0x36 (ivtv i2c driver #1) >> ivtv1: Registered device video1 for encoder MPG (4096 kB) >> ivtv1: Registered device video33 for encoder YUV (2048 kB) >> ivtv1: Registered device vbi1 for encoder VBI (1024 kB) >> ivtv1: Registered device video25 for encoder PCM (320 kB) >> ivtv1: Initialized card #1: WinTV PVR 500 (unit #2) >> ivtv: End initialization >> ivtv0: Loaded v4l-cx2341x-enc.fw firmware (376836 bytes) >> ivtv0: Encoder revision: 0x02060039 >> ivtv1: Loaded v4l-cx2341x-enc.fw firmware (376836 bytes) >> ivtv1: Encoder revision: 0x02060039 >> >> Does anyone have a clue where to look for further information? >> >> Kind regards, >> >> Luc > > > > _______________________________________________ > ivtv-users mailing list > [email protected] > http://ivtvdriver.org/mailman/listinfo/ivtv-users > _______________________________________________ ivtv-users mailing list [email protected] http://ivtvdriver.org/mailman/listinfo/ivtv-users
