2015-06-18 17:11 GMT+02:00 Zefir Kurtisi <[email protected]>: > On 06/18/2015 04:13 PM, Nick Kossifidis wrote: >> [...] >> I have NDA documents as well stating that the indices are from -64 to >> 63 (-64 to -1, 1 to 63 and 0 is DC), you can check out for yourself >> that we get 128bins on dynamic HT20/40, see the header files too: >> >> #define SPECTRAL_HT20_40_NUM_BINS 128 >> > Right, there are 128 in total, combined from 2 individual 64-bin sets. That's > why > you need to swap upper and lower when operating in HT40MINUS, since chip > always > puts primary channel to lower bin set. > >> and/or the received packet length. Maybe you are talking about >> "static" HT40 (I don't see anything about that on the documents I >> have) or something else. >> > Yes, maybe different documents. Mine says that interpretation of upper/lower > bin > values (max_magnitude, bitmap_weight, max_index) is the same in static and > dynamic > modes - only the bin values differ. > >>> I used the proposed method with the chirp detector for FFTs provided for >>> long >>> radar pulses on an AR9590 (patch posted the same day). Max bin index is >>> used there >>> the same way as with spectral, but now I realize my mistake: for chirp >>> detection, >>> the relative max_index is sufficient, while for spectral the absolute value >>> is needed. >>> >>> Toggling the MSB in HT20 shifts the signed values by 32 and leaves the >>> index with >>> an offset of 4, therefore the correct operation should be: >>> ht20_max_index_absolute = (ht20_max_index ^ 0x20) - 4 >>> >> >> Have in mind that on earlier chips (I did the testing on an AR9820) we >> get corrupted frames sometimes so we also need the sanity check I put >> there or else we can end up reading data out of bounds which is pretty >> dangerous so please leave the current implementation there as is. >> >> > The sanity checks / fixes are done before you look at the bin attributes and, > which therefore is not relevant for interpreting them. >
Only the lower boundary is checked (in case we are missing a byte -and we assume it's the first sample-), if we get a corrupted max_idx that's higher than 64 or 128 and we don't do the check on spectral_max_index, we 'll have issues when accessing the samples array to do the magnitude verification. -- GPG ID: 0xEE878588 As you read this post global entropy rises. Have Fun ;-) Nick -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
