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MMDVM
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A working fixed point Goertzel based on simulations.

This commit is contained in:
Jonathan Naylor 2020-04-23 12:36:34 +01:00
parent f19009b132
commit bf5ad25609
2 changed files with 14 additions and 12 deletions
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24
FMCTCSSRX.cpp
View File

@ -22,7 +22,7 @@
const struct CTCSS_TABLE {
uint8_t frequency;
q31_t coeffDivTwo;
q63_t coeffDivTwo;
} CTCSS_TABLE_DATA[] = {
{ 67U, 2147153298},
{ 69U, 2147130228},
@ -111,32 +111,34 @@ CTCSSState CFMCTCSSRX::process(q15_t sample)
{
m_result = m_result & (~CTS_READY);
q31_t samp = q31_t(sample) << 16;
q31_t q2 = m_q1;
m_q1 = m_q0;
// Q31 multiplication, t3 = m_coeffDivTwo * 2 * m_q1
q63_t t1 = m_coeffDivTwo * m_q1;
q31_t t2 = __SSAT((t1 >> 32), 31);
q31_t t2 = __SSAT((t1 >> 31), 31);
q31_t t3 = t2 * 2;
// m_q0 = m_coeffDivTwo * m_q1 * 2 - q2 + sample
m_q0 = t3 - q2 + q31_t(sample);
// m_q0 = m_coeffDivTwo * m_q1 * 2 - q2 + samp
m_q0 = t3 - q2 + samp;
m_count++;
if (m_count == N) {
// Q31 multiplication, t2 = m_q0 * m_q0
q63_t t1 = m_q0 * m_q0;
q31_t t2 = __SSAT((t1 >> 32), 31);
q63_t t1 = q63_t(m_q0) * q63_t(m_q0);
q31_t t2 = __SSAT((t1 >> 31), 31);
// Q31 multiplication, t4 = m_q0 * m_q0
q63_t t3 = m_q1 * m_q1;
q31_t t4 = __SSAT((t3 >> 32), 31);
q63_t t3 = q63_t(m_q1) * q63_t(m_q1);
q31_t t4 = __SSAT((t3 >> 31), 31);
// Q31 multiplication, t9 = m_q0 * m_q1 * m_coeffDivTwo * 2
q63_t t5 = m_q0 * m_q1;
q31_t t6 = __SSAT((t5 >> 32), 31);
q63_t t5 = q63_t(m_q0) * q63_t(m_q1);
q31_t t6 = __SSAT((t5 >> 31), 31);
q63_t t7 = t6 * m_coeffDivTwo;
q31_t t8 = __SSAT((t7 >> 32), 31);
q31_t t8 = __SSAT((t7 >> 31), 31);
q31_t t9 = t8 * 2;
// value = m_q0 * m_q0 + m_q1 * m_q1 - m_q0 * m_q1 * m_coeffDivTwo * 2

2
FMCTCSSRX.h
View File

@ -62,7 +62,7 @@ public:
void reset();
private:
q31_t m_coeffDivTwo;
q63_t m_coeffDivTwo;
q31_t m_threshold;
uint16_t m_count;
q31_t m_q0;