marcel.wiesweg@xxxxxx(Marcel Wiesweg) 22.06.05 19:09 >Am Mittwoch 22 Juni 2005 00:10 schrieb Rainer Zocholl: >> udo_richter@xxxxxx(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
