From 5d1a54eee54f41a505508729e9de4220b283c339 Mon Sep 17 00:00:00 2001 From: Andy CA6JAU Date: Mon, 10 Apr 2017 00:30:45 -0300 Subject: [PATCH] Improving DC filter for D-Star --- DStarRX.cpp | 18 ++++++++++-------- DStarRX.h | 4 ++-- 2 files changed, 12 insertions(+), 10 deletions(-) diff --git a/DStarRX.cpp b/DStarRX.cpp index 97958b7..5cb692c 100644 --- a/DStarRX.cpp +++ b/DStarRX.cpp @@ -35,9 +35,9 @@ const unsigned int SYNC_POS = 21U * DSTAR_DATA_LENGTH_BITS; const unsigned int SYNC_SCAN_START = SYNC_POS - 3U; const unsigned int SYNC_SCAN_END = SYNC_POS + 3U; -// Generated using [b, a] = butter(1, 0.002) in MATLAB -static q15_t DC_FILTER[] = {103, 0, 103, 0, 32563, 0}; // {b0, 0, b1, b2, -a1, -a2} -const uint16_t DC_FILTER_STAGES = 1U; // One Biquad stage +// Generated using [b, a] = butter(1, 0.001) in MATLAB +static q31_t DC_FILTER[] = {3367972, 0, 3367972, 0, 2140747704, 0}; // {b0, 0, b1, b2, -a1, -a2} +const uint32_t DC_FILTER_STAGES = 1U; // One Biquad stage // D-Star bit order version of 0x55 0x55 0x6E 0x0A const uint32_t FRAME_SYNC_DATA = 0x00557650U; @@ -266,7 +266,7 @@ m_rssiCount(0U), m_dcFilter(), m_dcState() { - ::memset(m_dcState, 0x00U, 4U * sizeof(q15_t)); + ::memset(m_dcState, 0x00U, 4U * sizeof(q31_t)); m_dcFilter.numStages = DC_FILTER_STAGES; m_dcFilter.pState = m_dcState; @@ -289,12 +289,14 @@ void CDStarRX::reset() void CDStarRX::samples(const q15_t* samples, const uint16_t* rssi, uint8_t length) { q31_t dc_level = 0; - q15_t dcVals[20]; + q31_t dcVals[20]; + q31_t intSamp[20]; - ::arm_biquad_cascade_df1_q15(&m_dcFilter, (q15_t*)samples, dcVals, length); + ::arm_q15_to_q31((q15_t*)samples, intSamp, length); + ::arm_biquad_cascade_df1_q31(&m_dcFilter, intSamp, dcVals, length); for (uint8_t i = 0U; i < length; i++) - dc_level += q31_t(dcVals[i]); + dc_level += dcVals[i]; dc_level /= length; @@ -302,7 +304,7 @@ void CDStarRX::samples(const q15_t* samples, const uint16_t* rssi, uint8_t lengt m_rssiAccum += rssi[i]; m_rssiCount++; - bool bit = samples[i] < q15_t(dc_level); + bool bit = samples[i] < (q15_t) (dc_level >> 16); if (bit != m_prev) { if (m_pll < (PLLMAX / 2U)) diff --git a/DStarRX.h b/DStarRX.h index 6246978..157fb41 100644 --- a/DStarRX.h +++ b/DStarRX.h @@ -53,8 +53,8 @@ private: uint8_t m_fecOutput[42U]; uint32_t m_rssiAccum; uint16_t m_rssiCount; - arm_biquad_casd_df1_inst_q15 m_dcFilter; - q15_t m_dcState[4]; + arm_biquad_casd_df1_inst_q31 m_dcFilter; + q31_t m_dcState[4]; void processNone(bool bit); void processHeader(bool bit);