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base repository: ngscopeclient/scopehal
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head repository: ngscopeclient/scopehal
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compare: 0c22ea097fa9
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  • 1 commit
  • 1 file changed
  • 1 contributor

Commits on May 12, 2021

  1. Ethernet100BaseTDecoder: added early-outs so we don't descramble the … 

    …entire waveform if the sync offset is wrong. Massive (order of magnitude) speedups.
    @azonenberg
    azonenberg committed May 12, 2021
    Copy the full SHA
    0c22ea0 View commit details
Showing with 19 additions and 9 deletions.
  1. +19 −9 scopeprotocols/Ethernet100BaseTDecoder.cpp
28 changes: 19 additions & 9 deletions scopeprotocols/Ethernet100BaseTDecoder.cpp
View file
Original file line number Diff line number Diff line change
@@ -416,22 +416,32 @@ bool Ethernet100BaseTDecoder::TrySync(
( (!bits.m_samples[idle_offset + 10]) << 0 );

//Descramble
size_t len = bits.m_samples.size();
for(unsigned int i=idle_offset + 11; i<len && i<stop; i++)
stop = min(stop, bits.m_samples.size());
size_t start = idle_offset + 11;
size_t len = stop - start;
descrambled_bits.m_offsets.reserve(len);
descrambled_bits.m_durations.reserve(len);
descrambled_bits.m_samples.reserve(len);
size_t window = 64 + idle_offset + 11;
for(size_t i=start; i < stop; i++)
{
lfsr = (lfsr << 1) ^ ((lfsr >> 8)&1) ^ ((lfsr >> 10)&1);

descrambled_bits.m_offsets.push_back(bits.m_offsets[i]);
descrambled_bits.m_durations.push_back(bits.m_durations[i]);
bool b = bits.m_samples[i] ^ (lfsr & 1);
descrambled_bits.m_samples.push_back(b);
}

//We should have at least 64 "1" bits in a row once the descrambling is done.
//The minimum inter-frame gap is a lot bigger than this.
for(int i=0; i<64; i++)
{
if(descrambled_bits.m_samples[i + idle_offset + 11] != 1)
return false;
if(descrambled_bits.m_samples.size() == window)
{
//We should have at least 64 "1" bits in a row once the descrambling is done.
//The minimum inter-frame gap is a lot bigger than this.
for(int j=0; j<64; j++)
{
if(descrambled_bits.m_samples[j + idle_offset + 11] != 1)
return false;
}
}
}

//Synced, all good