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MicroAPRS/Modem/afsk.c

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#include "afsk.h"
#include "config.h"
#include "hardware.h"
#include <drv/timer.h>
#include <cfg/module.h>
#define HDLC_FLAG 0x7E
#define HDLC_RESET 0x7F
#define AX25_ESC 0x1B
#include <cfg/log.h>
#include <cpu/power.h>
#include <cpu/pgm.h>
#include <struct/fifobuf.h>
#include <string.h> /* memset */
#define PHASE_BIT 8
#define PHASE_INC 1
#define PHASE_MAX (SAMPLEPERBIT * PHASE_BIT)
#define PHASE_THRES (PHASE_MAX / 2) // - PHASE_BIT / 2)
// Modulator constants
#define MARK_FREQ 1200
#define MARK_INC (uint16_t)(DIV_ROUND(SIN_LEN * (uint32_t)MARK_FREQ, CONFIG_AFSK_DAC_SAMPLERATE))
#define SPACE_FREQ 2200
#define SPACE_INC (uint16_t)(DIV_ROUND(SIN_LEN * (uint32_t)SPACE_FREQ, CONFIG_AFSK_DAC_SAMPLERATE))
//Ensure sample rate is a multiple of bit rate
STATIC_ASSERT(!(CONFIG_AFSK_DAC_SAMPLERATE % BITRATE));
#define DAC_SAMPLEPERBIT (CONFIG_AFSK_DAC_SAMPLERATE / BITRATE)
/**
* Sine table for the first quarter of wave.
* The rest of the wave is computed from this first quarter.
* This table is used to generate the modulated data.
*/
static const uint8_t PROGMEM sin_table[] =
{
128, 129, 131, 132, 134, 135, 137, 138, 140, 142, 143, 145, 146, 148, 149, 151,
152, 154, 155, 157, 158, 160, 162, 163, 165, 166, 167, 169, 170, 172, 173, 175,
176, 178, 179, 181, 182, 183, 185, 186, 188, 189, 190, 192, 193, 194, 196, 197,
198, 200, 201, 202, 203, 205, 206, 207, 208, 210, 211, 212, 213, 214, 215, 217,
218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233,
234, 234, 235, 236, 237, 238, 238, 239, 240, 241, 241, 242, 243, 243, 244, 245,
245, 246, 246, 247, 248, 248, 249, 249, 250, 250, 250, 251, 251, 252, 252, 252,
253, 253, 253, 253, 254, 254, 254, 254, 254, 255, 255, 255, 255, 255, 255, 255,
};
#define SIN_LEN 512 ///< Full wave length
STATIC_ASSERT(sizeof(sin_table) == SIN_LEN / 4);
/**
* Given the index, this function computes the correct sine sample
* based only on the first quarter of wave.
*/
INLINE uint8_t sin_sample(uint16_t idx)
{
ASSERT(idx < SIN_LEN);
uint16_t new_idx = idx % (SIN_LEN / 2);
new_idx = (new_idx >= (SIN_LEN / 4)) ? (SIN_LEN / 2 - new_idx - 1) : new_idx;
uint8_t data = pgm_read8(&sin_table[new_idx]);
return (idx >= (SIN_LEN / 2)) ? (255 - data) : data;
}
#define BIT_DIFFER(bitline1, bitline2) (((bitline1) ^ (bitline2)) & 0x01)
#define EDGE_FOUND(bitline) BIT_DIFFER((bitline), (bitline) >> 1)
/**
* High-Level Data Link Control parsing function.
* Parse bitstream in order to find characters.
*
* \param hdlc HDLC context.
* \param bit current bit to be parsed.
* \param fifo FIFO buffer used to push characters.
*
* \return true if all is ok, false if the fifo is full.
*/
static bool hdlc_parse(Hdlc *hdlc, bool bit, FIFOBuffer *fifo)
{
bool ret = true;
hdlc->demod_bits <<= 1;
hdlc->demod_bits |= bit ? 1 : 0;
/* HDLC Flag */
if (hdlc->demod_bits == HDLC_FLAG)
{
if (!fifo_isfull(fifo))
{
fifo_push(fifo, HDLC_FLAG);
hdlc->rxstart = true;
}
else
{
ret = false;
hdlc->rxstart = false;
}
hdlc->currchar = 0;
hdlc->bit_idx = 0;
return ret;
}
/* Reset */
if ((hdlc->demod_bits & HDLC_RESET) == HDLC_RESET)
{
hdlc->rxstart = false;
return ret;
}
if (!hdlc->rxstart)
return ret;
/* Stuffed bit */
if ((hdlc->demod_bits & 0x3f) == 0x3e)
return ret;
if (hdlc->demod_bits & 0x01)
hdlc->currchar |= 0x80;
if (++hdlc->bit_idx >= 8)
{
if ((hdlc->currchar == HDLC_FLAG
|| hdlc->currchar == HDLC_RESET
|| hdlc->currchar == AX25_ESC))
{
if (!fifo_isfull(fifo))
fifo_push(fifo, AX25_ESC);
else
{
hdlc->rxstart = false;
ret = false;
}
}
if (!fifo_isfull(fifo))
fifo_push(fifo, hdlc->currchar);
else
{
hdlc->rxstart = false;
ret = false;
}
hdlc->currchar = 0;
hdlc->bit_idx = 0;
}
else
hdlc->currchar >>= 1;
return ret;
}
/**
* ADC ISR callback.
* This function has to be called by the ADC ISR when a sample of the configured
* channel is available.
* \param af Afsk context to operate on.
* \param curr_sample current sample from the ADC.
*/
void afsk_adc_isr(Afsk *af, int8_t curr_sample)
{
AFSK_STROBE_ON();
/*
* 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);
/*
* 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.
*/
af->iir_x[0] = af->iir_x[1];
#if (CONFIG_AFSK_FILTER == AFSK_BUTTERWORTH)
af->iir_x[1] = ((int8_t)fifo_pop(&af->delay_fifo) * curr_sample) >> 2;
//af->iir_x[1] = ((int8_t)fifo_pop(&af->delay_fifo) * curr_sample) / 6.027339492;
#elif (CONFIG_AFSK_FILTER == AFSK_CHEBYSHEV)
af->iir_x[1] = ((int8_t)fifo_pop(&af->delay_fifo) * curr_sample) >> 2;
//af->iir_x[1] = ((int8_t)fifo_pop(&af->delay_fifo) * curr_sample) / 3.558147322;
#else
#error Filter type not found!
#endif
af->iir_y[0] = af->iir_y[1];
#if CONFIG_AFSK_FILTER == AFSK_BUTTERWORTH
/*
* This strange sum + shift is an optimization for af->iir_y[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->iir_y[1] = af->iir_x[0] + af->iir_x[1] + (af->iir_y[0] >> 1) + (af->iir_y[0] >> 3) + (af->iir_y[0] >> 5);
//af->iir_y[1] = af->iir_x[0] + af->iir_x[1] + af->iir_y[0] * 0.6681786379;
#elif CONFIG_AFSK_FILTER == AFSK_CHEBYSHEV
/*
* This should be (af->iir_y[0] * 0.438) but
* (af->iir_y[0] >> 1) is a faster approximation :-)
*/
af->iir_y[1] = af->iir_x[0] + af->iir_x[1] + (af->iir_y[0] >> 1);
//af->iir_y[1] = af->iir_x[0] + af->iir_x[1] + af->iir_y[0] * 0.4379097269;
#endif
/* Save this sampled bit in a delay line */
af->sampled_bits <<= 1;
af->sampled_bits |= (af->iir_y[1] > 0) ? 1 : 0;
/* Store current ADC sample in the af->delay_fifo */
fifo_push(&af->delay_fifo, curr_sample);
/* If there is an edge, adjust phase sampling */
if (EDGE_FOUND(af->sampled_bits))
{
if (af->curr_phase < PHASE_THRES)
af->curr_phase += PHASE_INC;
else
af->curr_phase -= PHASE_INC;
}
af->curr_phase += PHASE_BIT;
/* sample the bit */
if (af->curr_phase >= PHASE_MAX)
{
af->curr_phase %= PHASE_MAX;
/* Shift 1 position in the shift register of the found bits */
af->found_bits <<= 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(SAMPLEPERBIT == 8);
uint8_t bits = af->sampled_bits & 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->found_bits |= 1;
/*
* NRZI coding: if 2 consecutive bits have the same value
* a 1 is received, otherwise it's a 0.
*/
if (!hdlc_parse(&af->hdlc, !EDGE_FOUND(af->found_bits), &af->rx_fifo))
af->status |= AFSK_RXFIFO_OVERRUN;
}
AFSK_STROBE_OFF();
}
static void afsk_txStart(Afsk *af)
{
if (!af->sending)
{
af->phase_inc = MARK_INC;
af->phase_acc = 0;
af->stuff_cnt = 0;
af->sending = true;
af->preamble_len = DIV_ROUND(CONFIG_AFSK_PREAMBLE_LEN * BITRATE, 8000);
AFSK_DAC_IRQ_START(af->dac_ch);
}
ATOMIC(af->trailer_len = DIV_ROUND(CONFIG_AFSK_TRAILER_LEN * BITRATE, 8000));
}
#define BIT_STUFF_LEN 5
#define SWITCH_TONE(inc) (((inc) == MARK_INC) ? SPACE_INC : MARK_INC)
/**
* DAC ISR callback.
* This function has to be called by the DAC ISR when a sample of the configured
* channel has been converted out.
*
* \param af Afsk context to operate on.
*
* \return The next DAC output sample.
*/
uint8_t afsk_dac_isr(Afsk *af)
{
AFSK_STROBE_ON();
/* Check if we are at a start of a sample cycle */
if (af->sample_count == 0)
{
if (af->tx_bit == 0)
{
/* We have just finished transimitting a char, get a new one. */
if (fifo_isempty(&af->tx_fifo) && af->trailer_len == 0)
{
AFSK_DAC_IRQ_STOP(af->dac_ch);
af->sending = false;
AFSK_STROBE_OFF();
return 0;
}
else
{
/*
* If we have just finished sending an unstuffed byte,
* reset bitstuff counter.
*/
if (!af->bit_stuff)
af->stuff_cnt = 0;
af->bit_stuff = true;
/*
* Handle preamble and trailer
*/
if (af->preamble_len == 0)
{
if (fifo_isempty(&af->tx_fifo))
{
af->trailer_len--;
af->curr_out = HDLC_FLAG;
}
else
af->curr_out = fifo_pop(&af->tx_fifo);
}
else
{
af->preamble_len--;
af->curr_out = HDLC_FLAG;
}
/* Handle char escape */
if (af->curr_out == AX25_ESC)
{
if (fifo_isempty(&af->tx_fifo))
{
AFSK_DAC_IRQ_STOP(af->dac_ch);
af->sending = false;
AFSK_STROBE_OFF();
return 0;
}
else
af->curr_out = fifo_pop(&af->tx_fifo);
}
else if (af->curr_out == HDLC_FLAG || af->curr_out == HDLC_RESET)
/* If these chars are not escaped disable bit stuffing */
af->bit_stuff = false;
}
/* Start with LSB mask */
af->tx_bit = 0x01;
}
/* check for bit stuffing */
if (af->bit_stuff && af->stuff_cnt >= BIT_STUFF_LEN)
{
/* If there are more than 5 ones in a row insert a 0 */
af->stuff_cnt = 0;
/* switch tone */
af->phase_inc = SWITCH_TONE(af->phase_inc);
}
else
{
/*
* NRZI: if we want to transmit a 1 the modulated frequency will stay
* unchanged; with a 0, there will be a change in the tone.
*/
if (af->curr_out & af->tx_bit)
{
/*
* Transmit a 1:
* - Stay on the previous tone
* - Increase bit stuff counter
*/
af->stuff_cnt++;
}
else
{
/*
* Transmit a 0:
* - Reset bit stuff counter
* - Switch tone
*/
af->stuff_cnt = 0;
af->phase_inc = SWITCH_TONE(af->phase_inc);
}
/* Go to the next bit */
af->tx_bit <<= 1;
}
af->sample_count = DAC_SAMPLEPERBIT;
}
/* Get new sample and put it out on the DAC */
af->phase_acc += af->phase_inc;
af->phase_acc %= SIN_LEN;
af->sample_count--;
AFSK_STROBE_OFF();
return sin_sample(af->phase_acc);
}
static size_t afsk_read(KFile *fd, void *_buf, size_t size)
{
Afsk *af = AFSK_CAST(fd);
uint8_t *buf = (uint8_t *)_buf;
#if CONFIG_AFSK_RXTIMEOUT == 0
while (size-- && !fifo_isempty_locked(&af->rx_fifo))
#else
while (size--)
#endif
{
#if CONFIG_AFSK_RXTIMEOUT != -1
ticks_t start = timer_clock();
#endif
while (fifo_isempty_locked(&af->rx_fifo))
{
cpu_relax();
#if CONFIG_AFSK_RXTIMEOUT != -1
if (timer_clock() - start > ms_to_ticks(CONFIG_AFSK_RXTIMEOUT))
return buf - (uint8_t *)_buf;
#endif
}
*buf++ = fifo_pop_locked(&af->rx_fifo);
}
return buf - (uint8_t *)_buf;
}
static size_t afsk_write(KFile *fd, const void *_buf, size_t size)
{
Afsk *af = AFSK_CAST(fd);
const uint8_t *buf = (const uint8_t *)_buf;
while (size--)
{
while (fifo_isfull_locked(&af->tx_fifo))
cpu_relax();
fifo_push_locked(&af->tx_fifo, *buf++);
afsk_txStart(af);
}
return buf - (const uint8_t *)_buf;
}
static int afsk_flush(KFile *fd)
{
Afsk *af = AFSK_CAST(fd);
while (af->sending)
cpu_relax();
return 0;
}
static int afsk_error(KFile *fd)
{
Afsk *af = AFSK_CAST(fd);
int err;
ATOMIC(err = af->status);
return err;
}
static void afsk_clearerr(KFile *fd)
{
Afsk *af = AFSK_CAST(fd);
ATOMIC(af->status = 0);
}
/**
* Initialize an AFSK1200 modem.
* \param af Afsk context to operate on.
* \param adc_ch ADC channel used by the demodulator.
* \param dac_ch DAC channel used by the modulator.
*/
void afsk_init(Afsk *af, int adc_ch, int dac_ch)
{
#if CONFIG_AFSK_RXTIMEOUT != -1
MOD_CHECK(timer);
#endif
memset(af, 0, sizeof(*af));
af->adc_ch = adc_ch;
af->dac_ch = dac_ch;
fifo_init(&af->delay_fifo, (uint8_t *)af->delay_buf, sizeof(af->delay_buf));
fifo_init(&af->rx_fifo, af->rx_buf, sizeof(af->rx_buf));
/* Fill sample FIFO with 0 */
for (int i = 0; i < SAMPLEPERBIT / 2; i++)
fifo_push(&af->delay_fifo, 0);
fifo_init(&af->tx_fifo, af->tx_buf, sizeof(af->tx_buf));
AFSK_ADC_INIT(adc_ch, af);
AFSK_DAC_INIT(dac_ch, af);
AFSK_STROBE_INIT();
//LOG_INFO("MARK_INC %d, SPACE_INC %d\n", MARK_INC, SPACE_INC);
DB(af->fd._type = KFT_AFSK);
af->fd.write = afsk_write;
af->fd.read = afsk_read;
af->fd.flush = afsk_flush;
af->fd.error = afsk_error;
af->fd.clearerr = afsk_clearerr;
af->phase_inc = MARK_INC;
}
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