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Merge pull request #80 from juribeparada/master 

Filter for DC level estimation for D-Star
c4fmdemod
Jonathan Naylor 2017-04-09 19:53:42 +01:00 committed by GitHub
parent 421031323d 132cde0864
commit ab3cdbc277
2 changed files with 24 additions and 3 deletions
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22
DStarRX.cpp
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@ -35,7 +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_START = SYNC_POS - 3U;
const unsigned int SYNC_SCAN_END = SYNC_POS + 3U; const unsigned int SYNC_SCAN_END = SYNC_POS + 3U;
const q15_t THRESHOLD = 0; // 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
// D-Star bit order version of 0x55 0x55 0x6E 0x0A // D-Star bit order version of 0x55 0x55 0x6E 0x0A
const uint32_t FRAME_SYNC_DATA = 0x00557650U; const uint32_t FRAME_SYNC_DATA = 0x00557650U;
@ -262,6 +264,12 @@ m_fecOutput(),
m_rssiAccum(0U), m_rssiAccum(0U),
m_rssiCount(0U) m_rssiCount(0U)
{ {
::memset(m_DCState, 0x00U, 4U * sizeof(q15_t));
m_DCFilter.numStages = DC_FILTER_STAGES;
m_DCFilter.pState = m_DCState;
m_DCFilter.pCoeffs = DC_FILTER;
m_DCFilter.postShift = 0;
} }
void CDStarRX::reset() void CDStarRX::reset()
@ -278,11 +286,21 @@ void CDStarRX::reset()
void CDStarRX::samples(const q15_t* samples, const uint16_t* rssi, uint8_t length) void CDStarRX::samples(const q15_t* samples, const uint16_t* rssi, uint8_t length)
{ {
q31_t dc_level = 0;
q15_t DCVals[20];
::arm_biquad_cascade_df1_q15(&m_DCFilter, (q15_t*)samples, DCVals, length);
for (uint8_t i = 0U; i < length; i++)
dc_level += (q31_t)DCVals[i];
dc_level /= length;
for (uint16_t i = 0U; i < length; i++) { for (uint16_t i = 0U; i < length; i++) {
m_rssiAccum += rssi[i]; m_rssiAccum += rssi[i];
m_rssiCount++; m_rssiCount++;
bool bit = samples[i] < THRESHOLD; bool bit = samples[i] < (q15_t)dc_level;
if (bit != m_prev) { if (bit != m_prev) {
if (m_pll < (PLLMAX / 2U)) if (m_pll < (PLLMAX / 2U))

3
DStarRX.h
View File

@ -54,6 +54,9 @@ private:
uint32_t m_rssiAccum; uint32_t m_rssiAccum;
uint16_t m_rssiCount; uint16_t m_rssiCount;
arm_biquad_casd_df1_inst_q15 m_DCFilter;
q15_t m_DCState[4];
void processNone(bool bit); void processNone(bool bit);
void processHeader(bool bit); void processHeader(bool bit);
void processData(bool bit); void processData(bool bit);