Hi Fred, > SBC analysis handles 8 samples at a time. The optimisation requires 8 samples > forming an "odd" block, followed by 8 samples, forming an "even" block. Until > now SBC was used for encoding 4, 8, 12, or 16 blocks in a frame. Reordering > took a frame and for each 16 samples (ie 2 blocks) it produced one "odd" block > and one "even" block. > A mSBC frame encodes 15 blocks of 8 samples. 14 blocks are processed as before, > two at a time. If 8 samples are remaining, it will form the first half of two > blocks (a bit of an "odd" block, and a bit of an "even" block). When processing > the next frame, we detect eight samples were missing at previous iteration and > the two block can be finished. > > This reordering is possible because only one sample is moved (x[-7]) AND the > first coefficient in the coef table is 0. Thus x[0] doesn't need to be set and > 0 can be used in calculation instead. Note that x[-7] is not used in > analysis for this block. > see: analysis_consts_fixed8_simd_odd. > > To detect that two blocks are not completed, the number of processed samples > can be used. This value is stored in position. position starts at > SBC_X_BUFFER_SIZE-72 and is decremented by 16 as long as two blocks can be > formed. If only 8 samples are remaining in input, then position is decremented > by 8 *arbitrarly*, thus indicating that some samples are pending. During next > frame reordering, position will be decremented by 8 again, back to a 16 > multiple. > > This logic works for SBC_X_BUFFER_SIZE-72 multiple of 16 and bigger than > 8*2*15+72=312 and less than 8*3*15+72=432. The current value of 328 matches this > constraint and X buffer is shifted every two frames (30 blocks) in mSBC. This > way, we don't need to care about x[-7] when shifting, we also know that it > won't be before X. > --- > sbc/sbc_primitives.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 58 insertions(+), 1 deletion(-) > > diff --git a/sbc/sbc_primitives.c b/sbc/sbc_primitives.c > index 319e625..9c6e56a 100644 > --- a/sbc/sbc_primitives.c > +++ b/sbc/sbc_primitives.c > @@ -6,6 +6,7 @@ > * Copyright (C) 2004-2010 Marcel Holtmann <marcel@xxxxxxxxxxxx> > * Copyright (C) 2004-2005 Henryk Ploetz <henryk@xxxxxxxxxxx> > * Copyright (C) 2005-2006 Brad Midgley <bmidgley@xxxxxxxxxxxx> > + * Copyright (C) 2012 Intel Corporation make it 2012-2013 now. Regards Marcel -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
