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Migrated adc_isr

This commit is contained in:
Mark Qvist 2014-04-03 23:51:33 +02:00
parent 3265f99e8f
commit 16fd081e4b
2 changed files with 54 additions and 97 deletions
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149
Modem/afsk.c
View File

@ -46,10 +46,10 @@ INLINE uint8_t sinSample(uint16_t i) {
#define EDGE_FOUND(bits) BITS_DIFFER((bits), (bits) >> 1)
// Phase sync constants
#define PHASE_BIT 8
#define PHASE_BITS 8
#define PHASE_INC 1
#define PHASE_MAX (SAMPLESPERBIT * PHASE_BIT)
#define PHASE_THRES (PHASE_MAX / 2)
#define PHASE_MAX (SAMPLESPERBIT * PHASE_BITS)
#define PHASE_THRESHOLD (PHASE_MAX / 2)
// Modulation constants
#define MARK_FREQ 1200
@ -138,110 +138,67 @@ static bool hdlcParse(Hdlc *hdlc, bool bit, FIFOBuffer *fifo)
}
void afsk_adc_isr(Afsk *afsk, int8_t currentSample) {
// To determine the received frequency, and thereby
// the bit of the sample, we multiply the sample by
// a sample delayed by (samples per bit / 2).
// We then lowpass-filter the sample with a first
// order 600Hz filter
void afsk_adc_isr(Afsk *af, int8_t curr_sample)
{
AFSK_STROBE_ON();
afsk->iirX[0] = afsk->iirX[1];
afsk->iirX[1] = ((int8_t)fifo_pop(&afsk->delayFifo) * currentSample) >> 2;
/*
* Frequency discriminator and LP IIR filter.
* This filter is designed to work
* at the given sample rate and bit rate.
*/
STATIC_ASSERT(SAMPLERATE == 9600);
STATIC_ASSERT(BITRATE == 1200);
afsk->iirY[0] = afsk->iirY[1];
afsk->iirY[1] = afsk->iirX[0] + afsk->iirX[1] + (afsk->iirY[0] >> 1);
/*
* Frequency discrimination is achieved by simply multiplying
* the sample with a delayed sample of (samples per bit) / 2.
* Then the signal is lowpass filtered with a first order,
* 600 Hz filter. The filter implementation is selectable
* through the CONFIG_AFSK_FILTER config variable.
*/
// Put the sampled bit in a delay-line
afsk->sampledBits <<= 1; // Bitshift everything 1 left
afsk->sampledBits |= (afsk->iirY[1] > 0) ? 1 : 0;
af->iirX[0] = af->iirX[1];
// Put the current raw sample in the delay FIFO
fifo_push(&afsk->delayFifo, currentSample);
#if (CONFIG_AFSK_FILTER == AFSK_BUTTERWORTH)
af->iirX[1] = ((int8_t)fifo_pop(&af->delayFifo) * curr_sample) >> 2;
//af->iirX[1] = ((int8_t)fifo_pop(&af->delayFifo) * curr_sample) / 6.027339492;
#elif (CONFIG_AFSK_FILTER == AFSK_CHEBYSHEV)
af->iirX[1] = ((int8_t)fifo_pop(&af->delayFifo) * curr_sample) >> 2;
//af->iirX[1] = ((int8_t)fifo_pop(&af->delayFifo) * curr_sample) / 3.558147322;
#else
#error Filter type not found!
#endif
af->iirY[0] = af->iirY[1];
#if CONFIG_AFSK_FILTER == AFSK_BUTTERWORTH
/*
* This strange sum + shift is an optimization for af->iirY[0] * 0.668.
* iir * 0.668 ~= (iir * 21) / 32 =
* = (iir * 16) / 32 + (iir * 4) / 32 + iir / 32 =
* = iir / 2 + iir / 8 + iir / 32 =
* = iir >> 1 + iir >> 3 + iir >> 5
*/
af->iirY[1] = af->iirX[0] + af->iirX[1] + (af->iirY[0] >> 1) + (af->iirY[0] >> 3) + (af->iirY[0] >> 5);
//af->iirY[1] = af->iirX[0] + af->iirX[1] + af->iirY[0] * 0.6681786379;
#elif CONFIG_AFSK_FILTER == AFSK_CHEBYSHEV
/*
* This should be (af->iirY[0] * 0.438) but
* (af->iirY[0] >> 1) is a faster approximation :-)
*/
af->iirY[1] = af->iirX[0] + af->iirX[1] + (af->iirY[0] >> 1);
//af->iirY[1] = af->iirX[0] + af->iirX[1] + af->iirY[0] * 0.4379097269;
#endif
/* Save this sampled bit in a delay line */
af->sampledBits <<= 1;
af->sampledBits |= (af->iirY[1] > 0) ? 1 : 0;
/* Store current ADC sample in the af->delayFifo */
fifo_push(&af->delayFifo, curr_sample);
/* If there is an edge, adjust phase sampling */
if (EDGE_FOUND(af->sampledBits))
{
if (af->currentPhase < PHASE_THRES)
af->currentPhase += PHASE_INC;
else
af->currentPhase -= PHASE_INC;
// If there is a signal transition, recalibrate
// sampling phase
if (EDGE_FOUND(afsk->sampledBits)) {
if (afsk->currentPhase < PHASE_THRESHOLD) {
afsk->currentPhase += PHASE_INC;
} else {
afsk->currentPhase -= PHASE_INC;
}
}
af->currentPhase += PHASE_BIT;
afsk->currentPhase += PHASE_BITS;
/* sample the bit */
if (af->currentPhase >= PHASE_MAX)
{
af->currentPhase %= PHASE_MAX;
// Look at the raw samples to determine the transmitted bit
if (afsk->currentPhase >= PHASE_MAX) {
afsk->currentPhase %= PHASE_MAX;
/* Shift 1 position in the shift register of the found bits */
af->actualBits <<= 1;
// Bitshift to make room for next bit
afsk->actualBits <<= 1;
/*
* Determine bit value by reading the last 3 sampled bits.
* If the number of ones is two or greater, the bit value is a 1,
* otherwise is a 0.
* This algorithm presumes that there are 8 samples per bit.
*/
STATIC_ASSERT(SAMPLESPERBIT == 8);
uint8_t bits = af->sampledBits & 0x07;
if (bits == 0x07 // 111, 3 bits set to 1
|| bits == 0x06 // 110, 2 bits
|| bits == 0x05 // 101, 2 bits
|| bits == 0x03 // 011, 2 bits
)
af->actualBits |= 1;
// Determine the actual bit value by reading the last
// 3 sampled bits. If there is two ore more 1's, the
// actual bit is a 1, otherwise a 0.
uint8_t bits = afsk->sampledBits & 0x07;
if (bits == 0x07 || // 111
bits == 0x06 || // 110
bits == 0x05 || // 101
bits == 0x03 // 011
) {
afsk->actualBits |= 1;
}
/*
* NRZI coding: if 2 consecutive bits have the same value
* a 1 is received, otherwise it's a 0.
*/
if (!hdlcParse(&af->hdlc, !EDGE_FOUND(af->actualBits), &af->rxFifo))
af->status |= RX_OVERRUN;
// Now we can pass the actual bit to the HDLC parser.
// We are using NRZI coding, so if 2 consecutive bits
// have the same value, we have a 1, otherwise a 0.
// We use the EDGE_FOUND function to determine this.
// We also check the return of the Link Control parser
// to check if an error occured.
if (!hdlcParse(&afsk->hdlc, !EDGE_FOUND(afsk->actualBits), &afsk->rxFifo)) {
afsk->status |= RX_OVERRUN;
}
}
AFSK_STROBE_OFF();
}
static void afsk_txStart(Afsk *af)

2
buildrev.h
View File

@ -1,2 +1,2 @@
#define VERS_BUILD 76
#define VERS_BUILD 81
#define VERS_HOST "vixen"