Geoffrey Hausheer wrote: >Is there any way to get the SNR with the current drivers for an HD5000? >I applied Taylor's patch to 2.6.13.2, and had no real problem getting >my HD5000 up and running. azap returns that a channel lock has >occurred, and I can record just fine, but azap always reports snr as >'ffff'. I know that my signal is marginal (I initially set the card >up in windows, and was only able to squeak out a SNR of ~17 on PBS, >but this was good enough to get reliable picture and sound). I need >to go outside and re-aim my antenna (for some reason, I can only get a >strong signal when my directional all-band is pointed backwards at the >transmitter), but I'd like to have the SNR available before I do that. >azap normally shows signal=00000, snr=ffff. ber=00000, unc=000000, >status=0x1f and flags=FE_HAS_LOCK >though I'll occasionally see unc jump up a bit. > >I don't want to seem impatient, I am very happy that the card works in >linux as is, but I'm just wondering if I did something wrong or >whether these stats aren't available with this card yet. > > The issue that you're describing is with the frontend driver, not the card driver. Mac has written an explanation of why this feature hasn't been implemented: Mac Michaels wrote: >This whole thing is kind of ugly for the lgdt330x chips. >They do not provide signal strength directly. Thus I do not >provide a signal strength. It is always set to 0. > >An Equalizer/Phase Tracker Mean Square Error value is >available VSB. Only Phase Tracker MSE is available for QAM. >This can be converted to signal to noise ratio (SNR) in db >with the formula: > >SNR=10 log(25600/MSE) > >where log is base 10 and MSE is either of the two readings. >For the lgdt3303 one reading is 19 bits long and the other >is 20 bits long. For the lgdt3302 both values are 19 bits >long, but the formulas are different from that above. > >Unfortunately the variable used to return the result is >unsigned 16 bits long so the values must be truncated. >lgdt330x driver returns the truncated raw MSE value. > >If the variable were longer the full value could be returned >without arbitrary truncation. > >If the variable were signed the driver could return the SNR >value in db. It must be signed because the formula returns >a negative value when the signal is less than the noise or >a positive value when the signal is greater than the noise. >The calculation is made using lookup tables since floating >point math is not allowed in kernel drivers. > ...so I don't know if that's gonna happen anytime soon. At least it works! ;-) -- Michael Krufky
