2015-06-18 12:36 GMT+02:00 Zefir Kurtisi <zefir.kurtisi@xxxxxxxxxxx>: > On 06/18/2015 10:43 AM, Nick Kossifidis wrote: >> max_index is a 6bit signed integer in both cases (sorry for the 5bit >> typo in the comments), so the current function handles it correctly >> for both HT20 and dynamic HT20/40 modes (I've tested it extensively). >> Also you don't handle the negative indices we get from the hardware >> (you just remove the sign). Have you tested this and if you did on >> which hardware did you do the test ? >> >> 2015-06-16 11:21 GMT+02:00 Zefir Kurtisi <zefir.kurtisi@xxxxxxxxxxx>: >>> [...] >>> +/* return the max magnitude from the all/upper/lower bins >>> + * >>> + * in HT20: 6-bit signed number of range -28 to +27 >>> + * in HT40: 6-bit unsigned number of range 0 to +63 >>> + * (upper sub-channel index 0 is DC) >>> + * >>> + * Correct interpretation of the value has to be done at caller >>> + */ > > The comment above is taken from developer NDA documents and should be correct. > With that, in HT40 mode the max_index value has to be taken as is, while in HT20 > it needs to be shifted to the unsigned range. > 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 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. > 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. -- 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 majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
