mirror of https://github.com/g4klx/MMDVM.git
Improving DC filter for D-Star
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parent
4f516a827f
commit
5d1a54eee5
18
DStarRX.cpp
18
DStarRX.cpp
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@ -35,9 +35,9 @@ const unsigned int SYNC_POS = 21U * DSTAR_DATA_LENGTH_BITS;
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const unsigned int SYNC_SCAN_START = SYNC_POS - 3U;
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const unsigned int SYNC_SCAN_END = SYNC_POS + 3U;
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// Generated using [b, a] = butter(1, 0.002) in MATLAB
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static q15_t DC_FILTER[] = {103, 0, 103, 0, 32563, 0}; // {b0, 0, b1, b2, -a1, -a2}
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const uint16_t DC_FILTER_STAGES = 1U; // One Biquad stage
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// Generated using [b, a] = butter(1, 0.001) in MATLAB
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static q31_t DC_FILTER[] = {3367972, 0, 3367972, 0, 2140747704, 0}; // {b0, 0, b1, b2, -a1, -a2}
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const uint32_t DC_FILTER_STAGES = 1U; // One Biquad stage
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// D-Star bit order version of 0x55 0x55 0x6E 0x0A
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const uint32_t FRAME_SYNC_DATA = 0x00557650U;
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@ -266,7 +266,7 @@ m_rssiCount(0U),
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m_dcFilter(),
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m_dcState()
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{
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::memset(m_dcState, 0x00U, 4U * sizeof(q15_t));
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::memset(m_dcState, 0x00U, 4U * sizeof(q31_t));
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m_dcFilter.numStages = DC_FILTER_STAGES;
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m_dcFilter.pState = m_dcState;
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@ -289,12 +289,14 @@ void CDStarRX::reset()
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void CDStarRX::samples(const q15_t* samples, const uint16_t* rssi, uint8_t length)
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{
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q31_t dc_level = 0;
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q15_t dcVals[20];
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q31_t dcVals[20];
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q31_t intSamp[20];
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::arm_biquad_cascade_df1_q15(&m_dcFilter, (q15_t*)samples, dcVals, length);
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::arm_q15_to_q31((q15_t*)samples, intSamp, length);
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::arm_biquad_cascade_df1_q31(&m_dcFilter, intSamp, dcVals, length);
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for (uint8_t i = 0U; i < length; i++)
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dc_level += q31_t(dcVals[i]);
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dc_level += dcVals[i];
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dc_level /= length;
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@ -302,7 +304,7 @@ void CDStarRX::samples(const q15_t* samples, const uint16_t* rssi, uint8_t lengt
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m_rssiAccum += rssi[i];
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m_rssiCount++;
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bool bit = samples[i] < q15_t(dc_level);
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bool bit = samples[i] < (q15_t) (dc_level >> 16);
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if (bit != m_prev) {
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if (m_pll < (PLLMAX / 2U))
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