marcel.wiesweg@gmx.de(Marcel Wiesweg) 22.06.05 19:09
Am Mittwoch 22 Juni 2005 00:10 schrieb Rainer Zocholl:
udo_richter@gmx.de(Udo Richter) 19.06.05 16:40
Klaus Schmidinger wrote:
Isn't all that data protected by CRC32 checksums? How could "garbage" get in there?
Maybe somebody should try to find out why that "garbage" is produced in the first place...
I've seen this - though at least one year ago - with bad reception due to bad weather. For half an hour, the system time was jumping back and forward like crazy, starting and stopping some timers. Luckily, all timers were repeating, so none of them was gone after reception was back.
So: Who is doing the CRC checks? Maybe it's turned off or only an error bit is set but nobody cares about in further processing? (Maybe the cause for "unkown picture type" too?)
It's very unlikely that garbage can so often pass a CRC32 check.
The TDT is not specified to contain a CRC32 checksum.
That makes (a bit) sense because that information is "transient" anyway (what's the use of a time 10 minutes ago when i woudl have to know it was 10min ago??)
Ok, then we can "forget" to use raw TDT to set system time.
All larger tables have this, NIT, EIT, SDT, also TOT. The "small" ones TDT and RST have no checksum.
So the only way use the time table would be to implement tests like "ntp" uses.
(taking at least 3 probes, limit the time skip to only few seconds etc.)
Rainer