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Add AX.25 Slot Time and P-Persist processing for simplex work.

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This commit is contained in:
Jonathan Naylor
2020-07-01 12:33:08 +01:00
parent 2c6e2c2a11
commit 29c8cf9414
6 changed files with 163 additions and 6 deletions
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AX25Demodulator.cpp
+54
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@@ -41,6 +41,18 @@ q15_t LPF_FILTER_COEFFS[] = {
-34, -47, -47, -40, -28, -17, -8, -2
};
// Lock low-pass filter taps (80Hz Bessel)
// scipy.signal:
// b, a = bessel(4, [80.0/(1200/2)], 'lowpass')
//
const uint8_t PLL_IIR_SIZE = 5U;
const float32_t PLL_LOCK_B[] = {
1.077063e-03,4.308253e-03,6.462379e-03,4.308253e-03,1.077063e-03};
const float32_t PLL_LOCK_A[] = {
1.000000e+00,-2.774567e+00,2.962960e+00,-1.437990e+00,2.668296e-01};
// 64 Hz loop filter.
// scipy.signal:
// loop_coeffs = firwin(9, [64.0/(1200/2)], width = None,
@@ -63,6 +75,9 @@ m_pllState(),
m_pllLast(false),
m_pllBits(1U),
m_pllCount(0.0F),
m_pllJitter(0.0F),
m_pllDCD(false),
m_iirHistory(),
m_hdlcOnes(0U),
m_hdlcFlag(false),
m_hdlcBuffer(0U),
@@ -78,6 +93,9 @@ m_hdlcState(AX25_IDLE)
m_pllFilter.numTaps = PLL_FILTER_LEN;
m_pllFilter.pState = m_pllState;
m_pllFilter.pCoeffs = PLL_FILTER_COEFFS;
for (uint8_t i = 0U; i < PLL_IIR_SIZE; i++)
m_iirHistory[i] = 0.0F;
}
bool CAX25Demodulator::process(q15_t* samples, uint8_t length, CAX25Frame& frame)
@@ -154,10 +172,20 @@ bool CAX25Demodulator::PLL(bool input)
if (m_pllCount > PLL_LIMIT)
m_pllCount -= SAMPLES_PER_SYMBOL;
float32_t adjust = m_pllBits > 16U ? 5.0F : 0.0F;
float32_t offset = m_pllCount / float32_t(m_pllBits);
float32_t jitter;
::arm_fir_f32(&m_pllFilter, &offset, &jitter, 1U);
if (!m_duplex) {
float32_t absOffset = adjust;
if (offset < 0.0F)
absOffset -= offset;
else
absOffset += offset;
m_pllJitter = iir(absOffset);
}
m_pllCount -= jitter / 2.0F;
m_pllBits = 1U;
} else {
@@ -260,3 +288,29 @@ void CAX25Demodulator::setTwist(int8_t n)
m_twist.setTwist(n);
}
bool CAX25Demodulator::isDCD()
{
if (m_pllJitter <= (SAMPLES_PER_SYMBOL * 0.03F))
m_pllDCD = true;
else if (m_pllJitter >= (SAMPLES_PER_SYMBOL * 0.15F))
m_pllDCD = false;
return m_pllDCD;
}
float32_t CAX25Demodulator::iir(float32_t input)
{
for (int8_t i = int8_t(PLL_IIR_SIZE) - 1; i != 0; i--)
m_iirHistory[i] = m_iirHistory[i - 1];
m_iirHistory[0] = input;
for (uint8_t i = 1U; i < PLL_IIR_SIZE; i++)
m_iirHistory[0] -= PLL_LOCK_A[i] * m_iirHistory[i];
float32_t result = 0.0F;
for (uint8_t i = 0U; i < PLL_IIR_SIZE; i++)
result += PLL_LOCK_B[i] * m_iirHistory[i];
return result;
}