Em Thu, 17 Jan 2013 11:33:46 +0200 Antti Palosaari <crope@xxxxxx> escreveu: > What goes to these units in general, dB conversion is done by the driver > about always. It is quite hard or even impossible to find out that > formula unless you has adjustable test signal generator. > > Also we could not offer always dBm as signal strength. This comes to > fact that only recent silicon RF-tuners are able to provide RF strength. > More traditionally that estimation is done by demod from IF/RF AGC, > which leads very, very, rough estimation. > > So at least for the signal strength it is impossible to require dBm. dB > for SNR is possible, but it is very hard due to lack of developers > knowledge and test equipment. SNR could be still forced to look like it > is in given dB scale. I think it is not big loss even though SNR values > reported are a little bit wrong. > > > About half year ago I looked how SNR was measured every demod we has: > > http://palosaari.fi/linux/v4l-dvb/snr_2012-05-21.txt > > as we can see there is currently only two style used: > 1) 0.1 dB (very common in new drivers) > 2) unknown (== mostly just raw register values) It could make sense to have an FE_SCALE_UNKNOWN for those drivers, if they can't converted into any of the supported scales. Btw, as agreed, on v11: - dB scale changed to 0.001 dB (not sure if this will bring much gain, as I doubt that demods have that much precision); - removed QoS nomenclature (I hope I didn't forget it left on some patch); - removed DTV_QOS_ENUM; - counters reset logic is now driver-specific (currently, resetting it at set_frontend callback on mb8620s); I'll be posting the patches after finishing the tests. What's left (probably we need more discussions): a) a flag to indicate a counter reset (my suggestion). Does it make sense? If so, where should it be? At fe_status_t? b) per-stats/per-dvb-property error indicator (Devin's suggestion). I don't think it is needed for statistics. Yet, it may be interesting for the other dvb properties. So, IMHO, I would do add it like: struct dtv_property { __u32 cmd; __s32 error; /* Linux error code when set/get this specific property */ __u32 reserved[2]; union { __u32 data; struct dtv_fe_stats st; struct { __u8 data[32]; __u32 len; __u32 reserved1[3]; void *reserved2; } buffer; } u; int result; } __attribute__ ((packed)); A patch adding this for statistics should be easy, as there's just one driver currently implementing it. Making the core and drivers handle per-property errors can be trickier and will require more work. But I'm still in doubt if it does make sense for stats. Devin? Cheers, Mauro -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
