[mythtv-users] [mythtv] Dark Picture/Image and IRQ Lockup bug with fix

jeremy smith yahoo at belynnandjeremy.xohost.com
Sat Sep 18 20:13:08 EDT 2004

Software:  The bttv driver for video capture cards with Fusion 8x8 PCI video

Version:  Tested on v 0.9.15.  Reports of the bug start with v 0.9.12.

Problem:  Dark image/picture occurs at random times.  Most often after
changing channels.

Cause:  It starts with an IRQ lockup.  However, as the driver recovers, it
configures the card again.  This is done in the init_bt848 subroutine.  As
expected, it sets brightness, contrast, hue and color/saturation.  It then
configures the luma decimation filter.  However, to set the filter bit it
simply writes to the entire O_CONTROL and E_CONTROL registers, as opposed to
masking the bit.  The O_CONTROL and E_CONTROL registers also contain the MSB
of the saturation/color and contrast values.  Thus, the MSB data that was
just setup a few statements above is lost.

Fix:  Move the statements that set the brightness, contrast, hue and
color/saturation to after the luma decimation filter.  There are 4 lines,
starting at 1056.  Move them to 1068.

Ref:  http://www.domenech.org/bt878a-adc/conexant-fusion_878a_datasheet.pdf

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