I have a Hauppauge DVB-T PCI card (original with L64781 decoder) in a machine running Mandriva 2006 (kernel 2.6.12-14) and using the stock kernel drivers. The CPU is an Athlon XP-M 2500+. To keep the power consumption of the machine down I use 'Athcool'. This utility tweaks registers on the Northbridge chip so that when the CPU is idle it goes into a 'deep sleep' mode where is uses very little power. The downside is that it takes much longer for the processor to resume, so interrupt latency is greatly increased, though I have never before seen any problem in use. I get fairly poor reception of UK Freeview on the system, and an aerial upgrade hasn't improved it much. I've just realised that Athcool may be to blame. This is the output of 'dvbtune -m' on C5 with Athcool running: Signal=14135, Verror=11891, SNR=40349dB, BlockErrors=99, (S|L|C|V|SY|) Signal=14135, Verror=13445, SNR=39578dB, BlockErrors=191, (S|L|C|V|SY|) Signal=14135, Verror=12998, SNR=42662dB, BlockErrors=188, (S|L|C|V|SY|) And this is with it off: Signal=14135, Verror=1497, SNR=51143dB, BlockErrors=0, (S|L|C|V|SY|) Signal=14135, Verror=1385, SNR=50115dB, BlockErrors=0, (S|L|C|V|SY|) Signal=14135, Verror=1366, SNR=51143dB, BlockErrors=0, (S|L|C|V|SY|) Tinkering with PCI parameters has no effect. Although I can imagine that high interrupt latency could corrupt the output from the card, I don't see how the SNR and Viterbi error rates can be affected, since AIUI decoding is done by the L64781 chip not the drivers. I'm wondering whether the problem is caused by power supply noise. Putting the processor to sleep between interrupts means that there is a much greater variation in power supply current than normal, and maybe the card's electronics don't have enough filtering. Interestingly the problem is most evident on the QAM64 channels, where noise around the A/D could have more effect. Before I delve into the electronics, is there any way in which the operation of the driver could be affected by interrupt latency such as to cause the effect I'm seeing? -- Dave
