diff options
| author | ghostop14 <ghostop14@gmail.com> | 2020-02-01 13:02:34 -0500 |
|---|---|---|
| committer | devnulling <devnulling@users.noreply.github.com> | 2020-02-04 09:08:55 -0800 |
| commit | 90c8e30e87c935176224728d2a28709cb6a7adab (patch) | |
| tree | 4a97b486b018e3de13962c08aba0e3f35a77fd15 /gr-dtv/lib/atsc | |
| parent | 5b38e99298d47da94e4436d810db550d9e7e4520 (diff) | |
Fix ATSC Flowgraphs and Allow Realtime Viewing
The ATSC RX flowgraph has been fixed to allow for proper decoding.
The original flowgraph had rate mismatches between the RX filter
and the FPLL block that prevented proper decoding. This version
also has a number of performance enhancements that ultimately allow
the stream to be watched in real-time. These changes capitalize
on new PRs for GR master branch. The ATSC RX filter was broken
into its 2 respective parts (an RRC block and a resampler). The
RRC block now uses the faster FFT RRC convenience wrapper, and the
PFB arb resampler was crushing performance. So the sampling rate
was adjusted to match the ATSC symbol rate*sps. This removed the
need for a resampler altogether, significantly reducing CPU load.
Processor core affinity based on a GRCon17 presentation was also
applied to separate out blocks and prevent thread migration.
Some cleanup was also done in the FPLL receiver block. Note that
in using this in real-time, performance enhancements in PR 3076
that has not been merged into master yet are also important. The
FPLL loop has some speedups due to the inlining of the NCO and
sincos functions, and takes advantage of the already-merged
cx_limited_range performance improvement in the FPLL loop too.
An additional change to support fast CC multiply on systems that
do not support the cx_limited_range compiler flag can be incorporated
once 3076 is merged. This block also is better annotated for
others to understand some of the design choices. Ultimately with
the networking block in grnet, smplayer can be pointed at the
flowgraph and TV watched in real-time. See the flowgraph for
additional notes.
Diffstat (limited to 'gr-dtv/lib/atsc')
| -rw-r--r-- | gr-dtv/lib/atsc/atsc_fpll_impl.cc | 33 |
1 files changed, 20 insertions, 13 deletions
diff --git a/gr-dtv/lib/atsc/atsc_fpll_impl.cc b/gr-dtv/lib/atsc/atsc_fpll_impl.cc index 71f24713ac..b85a38207d 100644 --- a/gr-dtv/lib/atsc/atsc_fpll_impl.cc +++ b/gr-dtv/lib/atsc/atsc_fpll_impl.cc @@ -41,32 +41,39 @@ int atsc_fpll_impl::work(int noutput_items, gr_vector_const_void_star& input_items, gr_vector_void_star& output_items) { + constexpr float alpha = 0.01; + constexpr float beta = alpha * alpha / 4.0; + const gr_complex* in = (const gr_complex*)input_items[0]; float* out = (float*)output_items[0]; + float a_cos, a_sin; + float x; + gr_complex result, filtered; for (int k = 0; k < noutput_items; k++) { - float a_cos, a_sin; - d_nco.step(); // increment phase d_nco.sincos(&a_sin, &a_cos); // compute cos and sin // Mix out carrier and output I-only signal - gr_complex result = in[k] * gr_complex(a_sin, a_cos); + + // PR Merge Note: Once the Costas Optimization PR #3076 merges, this + // line below helps with performance when cx_limited_range is not available + // such as on Macs and Windows. Once the merge happens I'll push an update. + // gr::fast_cc_multiply(result, in[k], gr_complex(a_sin, a_cos)); + result = in[k] * gr_complex(a_sin, a_cos); + out[k] = result.real(); // Update phase/freq error - gr_complex filtered = d_afc.filter(result); - float x = gr::fast_atan2f(filtered.imag(), filtered.real()); + filtered = d_afc.filter(result); + x = gr::fast_atan2f(filtered.imag(), filtered.real()); // avoid slamming filter with big transitions - static const float limit = GR_M_PI / 2.0; - if (x > limit) - x = limit; - else if (x < -limit) - x = -limit; - - static const float alpha = 0.01; - static const float beta = alpha * alpha / 4.0; + if (x > M_PI_2) + x = M_PI_2; + else if (x < -M_PI_2) + x = -M_PI_2; + d_nco.adjust_phase(alpha * x); d_nco.adjust_freq(beta * x); } |