[linux-dvb] Re: A/V dropouts in dvb-kernel driver

[Klaus Schmidinger <Klaus.Schmidinger@cadsoft.de>]

I've tracked down the problem somewhat more and found that
in ves1x93.c, in case 'FE_READ_STATUS', the 'sync' value
sometimes has somewhat strange values. Mostly, when it's
wrong, one of the lower two bits is 0 (sometimes even both),
so this would indicate that there _is_ VITERBI _and_ SYNC,
but no SIGNAL or CARRIER (which clearly can't be, because without
signal or carrier there can't be anything else).

As a workaround (since the actual problem apparently is inside the
VES1893 chip) I have added the following code, which re-reads the
'sync' value in case it doesn't make sense:

--- linux/drivers/media/dvb/frontends/ves1x93.c  2004-08-25 21:27:08.000000000 +0200
+++ linux/drivers/media/dvb/frontends/ves1x93.c  2004-09-11 15:03:09.000000000 +0200
@@ -452,6 +452,11 @@
        {
                fe_status_t *status = arg;
                u8 sync = ves1x93_readreg (i2c, 0x0e);
+               int maxtry = 10; // just for safety - let's not get stuck here
+               while ((sync & 0x03) != 0x03 && (sync & 0x0c) && maxtry--) {
+                       msleep(10);
+                       sync = ves1x93_readreg (i2c, 0x0e);
+                }
 
                *status = 0;
 

With this modification the dropouts are gone on my system.
Maybe somebody more familiar with the driver internals could comment
on this. Does it make sense?
Since it is in a hardware specific source file, it shouldn't have
any side effects on other hardware.

Maybe it should be even enhanced so that any 'sync' value that doesn't
have its '1' bits contiguously set starting at the lowest bit will be
considered faulty.

But first I'd appreciate if those who have dropouts with the dvb-kernel
driver (I believe there have been a few postings stating that) would
try this patch and report whether it fixes the problem for them.


Klaus