Hi,
A while back I posted a message indicating that I was having trouble
getting NICAM stereo to work *and* get a clear picture. I was finding that
in order to get a clear picture I had to de-tune down by about 7 notches
in xawtv. This de-tuning meant that the NICAM decoder could no longer lock
on to the signal.
I realised today that the poor quality I was getting was due to
high-frequency luminance changes that were only noticeable at small
resolutions (I usually use a 384x288 pixel window). By de-tuning I was
attenuating the picture signal which removed the distortions.
Having read the Bt848 manual, I enabled automatic luminance filtering in
the decoder which attempts to remove these artefacts at the appropriate
resolutions. Below is a patch to bttv-0.7.64.
I'd be interested to hear if anybody else has experienced this problem,
and also if there is a good reason why this filtering is turned off by
default in the driver.
--- bttv-driver.c.old Sun Apr 29 19:51:43 2001
+++ bttv-driver.c Mon Jun 11 20:17:08 2001
@@ -1331,6 +1333,9 @@
btwrite(virt_to_bus(btv->risc_jmp+2),
BT848_RISC_STRT_ADD);
+ btand(~BT848_CONTROL_LDEC, BT848_E_CONTROL);
+ btand(~BT848_CONTROL_LDEC, BT848_O_CONTROL);
+
/* enforce pll reprogramming */
btv->pll.pll_current = 0;
set_pll(btv);
@@ -2578,7 +2583,7 @@
btv->fbuffer=NULL;
/* btwrite(0, BT848_TDEC); */
btwrite(0x10, BT848_COLOR_CTL);
btwrite(0x00, BT848_CAP_CTL);
/* set planar and packed mode trigger points and */
/* set rising edge of inverted GPINTR pin as irq trigger */
@@ -2606,8 +2611,10 @@
btwrite(/*BT848_ADC_SYNC_T|*/
BT848_ADC_RESERVED|BT848_ADC_CRUSH, BT848_ADC);
- btwrite(BT848_CONTROL_LDEC, BT848_E_CONTROL);
- btwrite(BT848_CONTROL_LDEC, BT848_O_CONTROL);
+ btwrite(0, BT848_E_CONTROL);
+ btwrite(0, BT848_O_CONTROL);
btv->picture.colour=254<<7;
btv->picture.brightness=128<<8;
--
Jonathan Paisley
paisleyj@xxxxxxxxxxxxx
