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Remove any DC offset from before any further filtering takes place.

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This commit is contained in:
Jonathan Naylor 2017-07-16 18:57:15 +01:00
parent 9d1ebc0f8f
commit 8540964097
9 changed files with 23 additions and 25 deletions
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22
IO.cpp
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@ -33,7 +33,7 @@ static q15_t GAUSSIAN_0_5_FILTER[] = {8, 104, 760, 3158, 7421, 9866, 7421, 315
const uint16_t GAUSSIAN_0_5_FILTER_LEN = 12U;
// One symbol boxcar filter
static q15_t BOXCAR_FILTER[] = {3000, 3000, 3000, 3000, 3000, 0};
static q15_t BOXCAR_FILTER[] = {12000, 12000, 12000, 12000, 12000, 0};
const uint16_t BOXCAR_FILTER_LEN = 6U;
// Generated using [b, a] = butter(1, 0.001) in MATLAB
@ -73,7 +73,7 @@ m_dcState()
::memset(m_rrcState, 0x00U, 70U * sizeof(q15_t));
::memset(m_gaussianState, 0x00U, 40U * sizeof(q15_t));
::memset(m_boxcarState, 0x00U, 30U * sizeof(q15_t));
::memset(m_dcState, 0x00U, 4U * sizeof(q31_t));
::memset(m_dcState, 0x00U, 4U * sizeof(q31_t));
m_rrcFilter.numTaps = RRC_0_2_FILTER_LEN;
m_rrcFilter.pState = m_rrcState;
@ -88,8 +88,8 @@ m_dcState()
m_boxcarFilter.pCoeffs = BOXCAR_FILTER;
m_dcFilter.numStages = DC_FILTER_STAGES;
m_dcFilter.pState = m_dcState;
m_dcFilter.pCoeffs = DC_FILTER;
m_dcFilter.pState = m_dcState;
m_dcFilter.pCoeffs = DC_FILTER;
m_dcFilter.postShift = 0;
initInt();
@ -171,17 +171,19 @@ void CIO::process()
q31_t dcLevel = 0;
q31_t dcVals[20];
q31_t intSamp[20];
::arm_q15_to_q31((q15_t*)samples, intSamp, RX_BLOCK_SIZE);
::arm_biquad_cascade_df1_q31(&m_dcFilter, intSamp, dcVals, RX_BLOCK_SIZE);
q31_t q31Samples[20U];
::arm_q15_to_q31(samples, q31Samples, RX_BLOCK_SIZE);
::arm_biquad_cascade_df1_q31(&m_dcFilter, q31Samples, dcVals, RX_BLOCK_SIZE);
for (uint8_t i = 0U; i < RX_BLOCK_SIZE; i++)
dcLevel += dcVals[i];
dcLevel /= RX_BLOCK_SIZE;
q15_t offset = q15_t(dcLevel >> 16);
m_dcLevel = q15_t(dcLevel >> 16);
for (uint8_t i = 0U; i < RX_BLOCK_SIZE; i++)
samples[i] -= offset;
if (m_modemState == STATE_IDLE) {
if (m_dstarEnable) {