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Using 2 stage IIR filter

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This commit is contained in:
Geoffrey Merck 2020-04-23 21:16:52 +02:00
parent 22c40e1d96
commit 8ecd8b67f4
2 changed files with 14 additions and 38 deletions
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45
FM.cpp
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@ -20,18 +20,11 @@
#include "Globals.h"
#include "FM.h"
q15_t FILTER_COEFFS[] = {
-630, -842, -846, -634, -312, -53, -14, -251, -683, -1113, -1322, -1179, -718, -147, 234, 172,
-399, -1298, -2124, -2402, -1783, -201, 2051, 4399, 6169, 6827, 6169, 4399, 2051, -201, -1783, -2402,
-2124, -1298, -399, 172, 234, -147, -718, -1179, -1322, -1113, -683, -251, -14, -53, -312, -634,
-846, -842, -630};
const uint16_t FILTER_COEFFS_LEN = 51U;
// 2 stage IIR Butterworth filter generated using https://github.com/F4FXL/iir_fixed_point/blob/4f1e580a7dad9f8742d24a06edd14b62110ba6e4/gen_coeff.py
q15_t FILTER_COEFFS[] = {1105, 2210, 1105, 16384,-19003,7512, 14,//1st stage
16384,-32768,16384,16384,-31020,14751,14};//2nd stage
CFM::CFM() :
m_filterBuffer(NULL),
m_filterPosition(0U),
m_callsign(),
m_rfAck(),
m_ctcssRX(),
@ -46,13 +39,15 @@ m_holdoffTimer(),
m_kerchunkTimer(),
m_ackMinTimer(),
m_ackDelayTimer(),
m_hangTimer()
m_hangTimer(),
m_filter()
{
m_filterBuffer = new q15_t[FILTER_COEFFS_LEN];
arm_biquad_cascade_df1_init_q15(&m_filter, 2, FILTER_COEFFS, m_filterState, 0);
}
void CFM::samples(q15_t* samples, uint8_t length)
{
arm_biquad_casd_df1_inst_q15* filterPtr = &m_filter;
uint8_t i = 0;
for (; i < length; i++) {
q15_t currentSample = samples[i];//save to a local variable to avoid indirection on every access
@ -98,7 +93,8 @@ void CFM::samples(q15_t* samples, uint8_t length)
if (!m_callsign.isRunning() && !m_rfAck.isRunning())
currentSample += m_timeoutTone.getAudio();
currentSample = filter(currentSample);
//currentSample = filter(currentSample);
arm_biquad_cascade_df1_fast_q15(filterPtr, samples +i, &currentSample, 1);
currentSample += m_ctcssTX.getAudio();
@ -394,26 +390,3 @@ void CFM::beginRelaying()
m_timeoutTimer.start();
m_ackMinTimer.start();
}
q15_t CFM::filter(q15_t sample)
{
q15_t output = 0;
m_filterBuffer[m_filterPosition] = sample;
uint8_t iTaps = 0U;
for (int8_t i = m_filterPosition; i >= 0; i--) {
q31_t temp = FILTER_COEFFS[iTaps++] * m_filterBuffer[i];
output += q15_t(__SSAT((temp >> 15), 16));
}
for (int8_t i = FILTER_COEFFS_LEN - 1; i >= m_filterPosition; i--) {
q31_t temp = FILTER_COEFFS[iTaps++] * m_filterBuffer[i];
output += q15_t(__SSAT((temp >> 15), 16));
}
m_filterPosition = (m_filterPosition + 1U) % FILTER_COEFFS_LEN;
return output;
}