/* -*- mode: c; tab-width: 4; indent-tabs-mode: t; c-basic-offset: 4; coding: utf-8 -*- */ /************************************************************************************ ** ** ** UHSDR FIRMWARE ** ** ** **---------------------------------------------------------------------------------** ** Licence: GNU GPLv3, see LICENSE.md ** ************************************************************************************/ // Common #include "psk.h" #include #include #include "softdds.h" #include "uhsdr_digi_buffer.h" #include "ui_driver.h" // only necessary because of UiDriver_TextMsgPutChar #include "radio_management.h" // only necessary because of RadioManagement_Request_TxOff // RX,TX common constants #define PSK_SAMPLE_RATE 12000 // TODO This should come from elsewhere, to be fixed // RX constants #define PSK_BND_FLT_LEN 5 #define PSK_BUF_LEN (PSK_SAMPLE_RATE / PSK_OFFSET) // this must be an integer result without remainder and must be a multiple of 4 #define PSK_SHIFT_DIFF (1.0 * PSK_OFFSET / PSK_SAMPLE_RATE) // phase change between two samples of PSK_OFFSET Hz // TX constants #define SAMPLE_MAX 32766 // max amplitude of generated samples typedef struct { uint16_t rate; uint16_t tx_idx; uint8_t tx_char; uint16_t tx_bits; int16_t tx_wave_sign_next; int16_t tx_wave_sign_current; uint16_t tx_bit_phase; uint32_t tx_bit_len; int16_t tx_zeros; int16_t tx_ones; bool tx_win; float32_t rx_phase; float32_t rx_samples_in[PSK_BND_FLT_LEN]; float32_t rx_samples[PSK_BND_FLT_LEN]; int16_t rx_bnd_idx; float32_t rx_cos_prod[PSK_BUF_LEN]; float32_t rx_sin_prod[PSK_BUF_LEN]; float32_t rx_scmix[PSK_BUF_LEN]; int32_t rx_idx; int8_t rx_last_bit; float32_t rx_err; // could be of interest for tuning float32_t rx_last_symbol; int16_t rx_symbol_len; // how many buffers fit into one bit int16_t rx_symbol_idx; // float32_t rx_symbol_buf[PSK_MAX_SYMBOL_BUF]; uint32_t rx_word; psk_modulator_t tx_mod_state; float32_t rx_sum_sin; float32_t rx_sum_cos; } PskState_Internal_t; // table courtesy of fldigi pskvaricode.cxx static const uint16_t psk_varicode[] = { 0b1010101011, /* 0 - */ 0b1011011011, /* 1 - */ 0b1011101101, /* 2 - */ 0b1101110111, /* 3 - */ 0b1011101011, /* 4 - */ 0b1101011111, /* 5 - */ 0b1011101111, /* 6 - */ 0b1011111101, /* 7 - */ 0b1011111111, /* 8 - */ 0b11101111, /* 9 - */ 0b11101, /* 10 - */ 0b1101101111, /* 11 - */ 0b1011011101, /* 12 - */ 0b11111, /* 13 - */ 0b1101110101, /* 14 - */ 0b1110101011, /* 15 - */ 0b1011110111, /* 16 - */ 0b1011110101, /* 17 - */ 0b1110101101, /* 18 - */ 0b1110101111, /* 19 - */ 0b1101011011, /* 20 - */ 0b1101101011, /* 21 - */ 0b1101101101, /* 22 - */ 0b1101010111, /* 23 - */ 0b1101111011, /* 24 - */ 0b1101111101, /* 25 - */ 0b1110110111, /* 26 - _{*/
0b1101010101, /* 27 - */
0b1101011101, /* 28 - */
0b1110111011, /* 29 - */
0b1011111011, /* 30 - */
0b1101111111, /* 31 - */
0b1, /* 32 - */
0b111111111, /* 33 - ! */
0b101011111, /* 34 - '"' */
0b111110101, /* 35 - # */
0b111011011, /* 36 - $ */
0b1011010101, /* 37 - % */
0b1010111011, /* 38 - & */
0b101111111, /* 39 - ' */
0b11111011, /* 40 - ( */
0b11110111, /* 41 - ) */
0b101101111, /* 42 - * */
0b111011111, /* 43 - + */
0b1110101, /* 44 - , */
0b110101, /* 45 - - */
0b1010111, /* 46 - . */
0b110101111, /* 47 - / */
0b10110111, /* 48 - 0 */
0b10111101, /* 49 - 1 */
0b11101101, /* 50 - 2 */
0b11111111, /* 51 - 3 */
0b101110111, /* 52 - 4 */
0b101011011, /* 53 - 5 */
0b101101011, /* 54 - 6 */
0b110101101, /* 55 - 7 */
0b110101011, /* 56 - 8 */
0b110110111, /* 57 - 9 */
0b11110101, /* 58 - : */
0b110111101, /* 59 - ; */
0b111101101, /* 60 - < */
0b1010101, /* 61 - = */
0b111010111, /* 62 - > */
0b1010101111, /* 63 - ? */
0b1010111101, /* 64 - @ */
0b1111101, /* 65 - A */
0b11101011, /* 66 - B */
0b10101101, /* 67 - C */
0b10110101, /* 68 - D */
0b1110111, /* 69 - E */
0b11011011, /* 70 - F */
0b11111101, /* 71 - G */
0b101010101, /* 72 - H */
0b1111111, /* 73 - I */
0b111111101, /* 74 - J */
0b101111101, /* 75 - K */
0b11010111, /* 76 - L */
0b10111011, /* 77 - M */
0b11011101, /* 78 - N */
0b10101011, /* 79 - O */
0b11010101, /* 80 - P */
0b111011101, /* 81 - Q */
0b10101111, /* 82 - R */
0b1101111, /* 83 - S */
0b1101101, /* 84 - T */
0b101010111, /* 85 - U */
0b110110101, /* 86 - V */
0b101011101, /* 87 - W */
0b101110101, /* 88 - X */
0b101111011, /* 89 - Y */
0b1010101101, /* 90 - Z */
0b111110111, /* 91 - [ */
0b111101111, /* 92 - \ */
0b111111011, /* 93 - ] */
0b1010111111, /* 94 - ^ */
0b101101101, /* 95 - _ */
0b1011011111, /* 96 - ` */
0b1011, /* 97 - a */
0b1011111, /* 98 - b */
0b101111, /* 99 - c */
0b101101, /* 100 - d */
0b11, /* 101 - e */
0b111101, /* 102 - f */
0b1011011, /* 103 - g */
0b101011, /* 104 - h */
0b1101, /* 105 - i */
0b111101011, /* 106 - j */
0b10111111, /* 107 - k */
0b11011, /* 108 - l */
0b111011, /* 109 - m */
0b1111, /* 110 - n */
0b111, /* 111 - o */
0b111111, /* 112 - p */
0b110111111, /* 113 - q */
0b10101, /* 114 - r */
0b10111, /* 115 - s */
0b101, /* 116 - t */
0b110111, /* 117 - u */
0b1111011, /* 118 - v */
0b1101011, /* 119 - w */
0b11011111, /* 120 - x */
0b1011101, /* 121 - y */
0b111010101, /* 122 - z */
0b1010110111, /* 123 - { */
0b110111011, /* 124 - | */
0b1010110101, /* 125 - } */
0b1011010111, /* 126 - ~ */
0b1110110101, /* 127 - */
0b1110111101, /* 128 - */
0b1110111111, /* 129 - */
0b1111010101, /* 130 - */
0b1111010111, /* 131 - */
0b1111011011, /* 132 - */
0b1111011101, /* 133 - */
0b1111011111, /* 134 - */
0b1111101011, /* 135 - */
0b1111101101, /* 136 - */
0b1111101111, /* 137 - */
0b1111110101, /* 138 - */
0b1111110111, /* 139 - */
0b1111111011, /* 140 - */
0b1111111101, /* 141 - */
0b1111111111, /* 142 - */
0b10101010101, /* 143 - */
0b10101010111, /* 144 - */
0b10101011011, /* 145 - */
0b10101011101, /* 146 - */
0b10101011111, /* 147 - */
0b10101101011, /* 148 - */
0b10101101101, /* 149 - */
0b10101101111, /* 150 - */
0b10101110101, /* 151 - */
0b10101110111, /* 152 - */
0b10101111011, /* 153 - */
0b10101111101, /* 154 - */
0b10101111111, /* 155 - */
0b10110101011, /* 156 - */
0b10110101101, /* 157 - */
0b10110101111, /* 158 - */
0b10110110101, /* 159 - */
0b10110110111, /* 160 - */
0b10110111011, /* 161 - */
0b10110111101, /* 162 - */
0b10110111111, /* 163 - */
0b10111010101, /* 164 - */
0b10111010111, /* 165 - */
0b10111011011, /* 166 - */
0b10111011101, /* 167 - */
0b10111011111, /* 168 - */
0b10111101011, /* 169 - */
0b10111101101, /* 170 - */
0b10111101111, /* 171 - */
0b10111110101, /* 172 - */
0b10111110111, /* 173 - */
0b10111111011, /* 174 - */
0b10111111101, /* 175 - */
0b10111111111, /* 176 - */
0b11010101011, /* 177 - */
0b11010101101, /* 178 - */
0b11010101111, /* 179 - */
0b11010110101, /* 180 - */
0b11010110111, /* 181 - */
0b11010111011, /* 182 - */
0b11010111101, /* 183 - */
0b11010111111, /* 184 - */
0b11011010101, /* 185 - */
0b11011010111, /* 186 - */
0b11011011011, /* 187 - */
0b11011011101, /* 188 - */
0b11011011111, /* 189 - */
0b11011101011, /* 190 - */
0b11011101101, /* 191 - */
0b11011101111, /* 192 - */
0b11011110101, /* 193 - */
0b11011110111, /* 194 - */
0b11011111011, /* 195 - */
0b11011111101, /* 196 - */
0b11011111111, /* 197 - */
0b11101010101, /* 198 - */
0b11101010111, /* 199 - */
0b11101011011, /* 200 - */
0b11101011101, /* 201 - */
0b11101011111, /* 202 - */
0b11101101011, /* 203 - */
0b11101101101, /* 204 - */
0b11101101111, /* 205 - */
0b11101110101, /* 206 - */
0b11101110111, /* 207 - */
0b11101111011, /* 208 - */
0b11101111101, /* 209 - */
0b11101111111, /* 210 - */
0b11110101011, /* 211 - */
0b11110101101, /* 212 - */
0b11110101111, /* 213 - */
0b11110110101, /* 214 - */
0b11110110111, /* 215 - */
0b11110111011, /* 216 - */
0b11110111101, /* 217 - */
0b11110111111, /* 218 - */
0b11111010101, /* 219 - */
0b11111010111, /* 220 - */
0b11111011011, /* 221 - */
0b11111011101, /* 222 - */
0b11111011111, /* 223 - */
0b11111101011, /* 224 - */
0b11111101101, /* 225 - */
0b11111101111, /* 226 - */
0b11111110101, /* 227 - */
0b11111110111, /* 228 - */
0b11111111011, /* 229 - */
0b11111111101, /* 230 - */
0b11111111111, /* 231 - */
0b101010101011, /* 232 - */
0b101010101101, /* 233 - */
0b101010101111, /* 234 - */
0b101010110101, /* 235 - */
0b101010110111, /* 236 - */
0b101010111011, /* 237 - */
0b101010111101, /* 238 - */
0b101010111111, /* 239 - */
0b101011010101, /* 240 - */
0b101011010111, /* 241 - */
0b101011011011, /* 242 - */
0b101011011101, /* 243 - */
0b101011011111, /* 244 - */
0b101011101011, /* 245 - */
0b101011101101, /* 246 - */
0b101011101111, /* 247 - */
0b101011110101, /* 248 - */
0b101011110111, /* 249 - */
0b101011111011, /* 250 - */
0b101011111101, /* 251 - */
0b101011111111, /* 252 - */
0b101101010101, /* 253 - */
0b101101010111, /* 254 - */
0b101101011011, /* 255 - */
};

#define PSK_VARICODE_NUM (sizeof(psk_varicode)/sizeof(*psk_varicode))

static const float32_t PskBndPassB_31[] = {
6.6165543533213894e-05,
0.0,
-0.00013233108706642779,
0.0,
6.6165543533213894e-05
};

static const float32_t PskBndPassA_31[] = {
1.0,
-3.8414813063247664,
5.6662277107033248,
-3.7972899991488904,
0.9771256616899302
};

static const float32_t PskBndPassB_63[] = {
0.0002616526950658905,
0.0,
-0.000523305390131781,
0.0,
0.0002616526950658905
};

static const float32_t PskBndPassA_63[] = {
1.0,
-3.8195192250239174,
5.6013869366249818,
-3.7321386869273105,
0.95477455992103932
};

static const float32_t PskBndPassB_125[] = {
0.0010232176384709002,
0.0,
-0.0020464352769418003,
0.0,
0.0010232176384709002
};

static const float32_t PskBndPassA_125[] = {
1.0,
-3.7763786572915334,
5.4745855184361272,
-3.6055008493327723,
0.91159449659996006
};

static soft_dds_t psk_dds;
static soft_dds_t psk_bit_dds;
static soft_dds_t psk_rx_dds;

#if 0
static void PskBufAdd(int len, float32_t buf[], float32_t v)
{
for (int i = len - 1; i > 0; i--)
{
buf[i] = buf[i-1];
}
buf[0] = v;
}
#endif

static float32_t Psk_IirNext(const float32_t bpf_b[], const float32_t bpf_a[], float32_t x[], float32_t y[], int idx, int taps)
{
float32_t resp = 0;
int iidx;

for (int i = 0; i < taps; i++)
{
iidx = (idx - i + taps) % taps;
resp += bpf_b[i] * x[iidx];
if (i>0)
{
resp -= bpf_a[i] * y[iidx];
}
}
return resp / bpf_a[0];
}

const psk_speed_item_t psk_speeds[PSK_SPEED_NUM] =
{
{ .id =PSK_SPEED_31, .value = 31.25, .bpf_b = PskBndPassB_31, .bpf_a = PskBndPassA_31, .rate = 384, .label = " 31" },
{ .id =PSK_SPEED_63, .value = 62.5, .bpf_b = PskBndPassB_63, .bpf_a = PskBndPassA_63, .rate = 192, .label = " 63" },
{ .id =PSK_SPEED_125, .value = 125.0, .bpf_b = PskBndPassB_125, .bpf_a = PskBndPassA_125, .rate = 96, .label = "125" }
};

psk_ctrl_t psk_ctrl_config =
{
.speed_idx = PSK_SPEED_31
};

PskState_Internal_t psk_state;

static void Bpsk_ResetWin(void) {
// little trick, we just reset the acc
// which brings us back to the first sample
psk_bit_dds.acc = 0;
}

void Psk_Modulator_PrepareTx()
{
Psk_Modulator_SetState(PSK_MOD_PREAMBLE);
}

void Bpsk_Demodulator_Init()
{
psk_state.rx_phase = 0;
psk_state.rx_bnd_idx = 0;

for (int i = 0; i < PSK_BND_FLT_LEN; i++)
{
psk_state.rx_samples_in[i] = 0;
psk_state.rx_samples[i] = 0;
}

for (int i = 0; i < PSK_BUF_LEN; i++)
{
psk_state.rx_cos_prod[i] = 0;
psk_state.rx_sin_prod[i] = 0;
psk_state.rx_scmix[i] = 0;
}

psk_state.rx_idx = 0;
psk_state.rx_last_bit = 0;
psk_state.rx_last_symbol = 0;
psk_state.rx_symbol_len = psk_state.rate / PSK_BUF_LEN;
psk_state.rx_symbol_idx = 0;

// for (int i = 0; i < psk_state.rx_symbol_len; i ++)
// {
// psk_state.rx_symbol_buf[i];
// }

psk_state.rx_word = 0;
}

void Psk_Modem_Init(uint32_t output_sample_rate)
{

psk_state.tx_idx = 0;

softdds_setFreqDDS(&psk_dds, PSK_OFFSET, output_sample_rate, true);
softdds_setFreqDDS(&psk_rx_dds, PSK_OFFSET, PSK_SAMPLE_RATE, true);
// we use a sine wave with a frequency of half of the bit rate
// as envelope generator
softdds_setFreqDDS(&psk_bit_dds, (float32_t)psk_speeds[psk_ctrl_config.speed_idx].value / 2.0, output_sample_rate, false);

psk_state.tx_bit_len = lround(output_sample_rate / psk_speeds[psk_ctrl_config.speed_idx].value * 2); // 480000 / 31.25 * 2 = 3072
psk_state.rate = PSK_SAMPLE_RATE / psk_speeds[psk_ctrl_config.speed_idx].value;

Bpsk_Demodulator_Init();
}

static char Bpsk_DecodeVaricode(uint16_t code)
{
char result = '*';
for (int i = 0; i 0)
{
retval |= code & 0x1; // mask and transfer LSB
retval <<= 1; // left shift
code >>= 1; // right shift, next bit gets active
}

return retval;
}

/**
*
* Basically samples the phase every bit length based on a sample which is one full sine wave
* of the carrier frequency. So it is not using multiple sampling points or anything.
* We throw away a lot of phase differences symbols
* using more of these should make the code more robust, shouldn't it?
*
* @param symbol_out averaged phase of the samples.
*/

static void BpskDecoder_NextSymbol(float32_t symbol_out)
{
int8_t bit;

static float32_t symbol_store = 0;

// if (psk_state.rx_symbol_len - psk_state.rx_symbol_idx < 6)
{
symbol_store = symbol_out;
}

psk_state.rx_symbol_idx += 1;
if (psk_state.rx_symbol_idx >= psk_state.rx_symbol_len)
{
psk_state.rx_symbol_idx = 0;
// TODO here should come additional part to check if timing of sampling should be moved
if (psk_state.rx_last_symbol * symbol_store < 0)
{
bit = 0;
}
else
{
bit = 1;
}

psk_state.rx_last_symbol = symbol_store;
symbol_store = 0;

// have we found 2 consecutive 0 bits? And previously at least one received bit == 1?
// indicates an end of character
if (psk_state.rx_last_bit == 0 && bit == 0 && psk_state.rx_word != 0)
{
// we lookup up the bits received (minus the last zero, which we shift out to the right)
// and put it into the buffer
UiDriver_TextMsgPutChar(Bpsk_DecodeVaricode(psk_state.rx_word >> 1));

// clean out the stored bit pattern
psk_state.rx_word = 0;
}
else
{
psk_state.rx_word = (psk_state.rx_word << 1) | bit;
}

psk_state.rx_last_bit = bit;

}
}

static float32_t BpskDecoder_Bandpass(float32_t sample)
{
// save original sample in bpf's input buffer
psk_state.rx_samples_in[psk_state.rx_bnd_idx] = sample;

// IIR bandpass for signal frequency range, implemented in a ring buffer
float32_t retval = Psk_IirNext(psk_speeds[psk_ctrl_config.speed_idx].bpf_b, psk_speeds[psk_ctrl_config.speed_idx].bpf_a, psk_state.rx_samples_in,
psk_state.rx_samples, psk_state.rx_bnd_idx, PSK_BND_FLT_LEN);

// save filtered sample in state buffer, used in next run;
psk_state.rx_samples[psk_state.rx_bnd_idx] = retval;

// increment our ring buffer index
psk_state.rx_bnd_idx++;
psk_state.rx_bnd_idx %= PSK_BND_FLT_LEN;

return retval;
}

/**
* Process an audio sample and decode signal.
*
* @param audio sample at PSK_SAMPLE_RATE
*/
void Psk_Demodulator_ProcessSample(float32_t sample)
{
float32_t fsample = BpskDecoder_Bandpass(sample);

// VCO generates a sine/cosine wave "carrier" with PSK_OFFSET Hz as frequency
float32_t vco_sin, vco_cos;
// we have to use a different DDS as for TX (different sample rates), IQ gives us sin and cos waves of PSK_OFFSET Hz
softdds_genIQSingleTone(&psk_rx_dds, &vco_sin , &vco_cos, 1);

// we now multiple these carriers with our signal
// this allows us to compare phase differences
float32_t sin_mix = vco_sin * fsample;
float32_t cos_mix = vco_cos * fsample;

// update sums by differences between old and new value in ringbuffer
psk_state.rx_sum_sin += sin_mix - psk_state.rx_sin_prod[psk_state.rx_idx];
psk_state.rx_sum_cos += cos_mix - psk_state.rx_cos_prod[psk_state.rx_idx];

// store new value
psk_state.rx_sin_prod[psk_state.rx_idx] = sin_mix;
psk_state.rx_cos_prod[psk_state.rx_idx] = cos_mix;

// we now calculate an average
float32_t symbol_out = psk_state.rx_sum_sin / PSK_BUF_LEN;
float32_t cos_out = psk_state.rx_sum_cos / PSK_BUF_LEN;

// GUESS: now try to estimate the frequency error of our VCO vs. the incoming signal
float32_t rx_scmix = symbol_out * cos_out;
psk_state.rx_err += rx_scmix - psk_state.rx_scmix[psk_state.rx_idx];
psk_state.rx_scmix[psk_state.rx_idx] = rx_scmix;

float32_t smax = 0;

for (int i = 0; i < PSK_BUF_LEN; i++)
{
if (fabsf(psk_state.rx_cos_prod[i]) > smax)
{
smax = fabsf(psk_state.rx_cos_prod[i]);
}
if (fabsf(psk_state.rx_sin_prod[i]) > smax)
{
smax = fabsf(psk_state.rx_sin_prod[i]);
}
}

// calculate the final correction value from rx_err
// avoid division by zero if smax is 0
float32_t rx_err_corr = psk_state.rx_err/ (PSK_BUF_LEN * ((smax != 0) ? (smax * smax * 4.0) : 1.0));

// if the error is too large, we limit it to +/- 0.1
if(fabsf(rx_err_corr) > 0.1)
{
rx_err_corr = (rx_err_corr > 0) ? 0.1 : -0.1;
}
rx_err_corr = 0;

// now advance our phase counter with our error correction
psk_state.rx_phase += PSK_SHIFT_DIFF + rx_err_corr * PSK_SHIFT_DIFF;

// we just passed one "full" offset frequency wave length?
// now see if we have enough symbols to decide if it is a 1 or 0
// the symbol is basically an averaged phase difference over the last PSK_BUF_LEN
// samples.
if (psk_state.rx_phase > 1)
{
psk_state.rx_phase -= 1;
BpskDecoder_NextSymbol(symbol_out);
}

if (psk_state.rx_phase < 0)
{
psk_state.rx_phase += 1;
}

// we prepare us for the next sample in our ring buffer
psk_state.rx_idx = (psk_state.rx_idx + 1) % PSK_BUF_LEN;
}

static bool bit_start(uint16_t tx_bit_phase)
{
return tx_bit_phase == psk_state.tx_bit_len / 4;
}

static bool bit_middle(uint16_t tx_bit_phase)
{
return tx_bit_phase == 0;
}

/**
* Generates a BPSK signal. Uses an oscillator for generating continous base signal of a
* given frequency (defined in PSK_OFFSET). This signal is phase controlled by a variable
* psk_state.tx_wave_sign_current. A second frequency generator provides an envelope shape based on a cosine
* of half of the bpsk rate. For 0 bits to transmit the symbol is using the enveloped signal and shifts
* in the middle.
*
*
* @return
*/
int16_t Psk_Modulator_GenSample()
{
// tx_bit_len / 4 -> start of a bit
// tx_bit_len / 0 -> middle of a bit
// tx_bit_len / 2 -> end of a bit

int32_t retval = 0; // by default we produce silence

// check if the modulator is supposed to be active...
if (Psk_Modulator_GetState() != PSK_MOD_OFF)
{
// try to find out what to transmit next
if (bit_start(psk_state.tx_bit_phase))
{
// check if we still have bits to transmit
if (psk_state.tx_bits == 0)
{
// no, all bits have been transmitted
if (psk_state.tx_zeros < 2 || (Psk_Modulator_GetState() == PSK_MOD_PREAMBLE))
{
// send spacing zeros before anything else happens
// normal characters don't have 2 zeros following each other
psk_state.tx_zeros++;

// are we sending a preamble and have transmitted enough zeroes?
// we do this for roughly a second, i.e. we simply use the rate as "timer"
if ((Psk_Modulator_GetState() == PSK_MOD_PREAMBLE) && psk_state.tx_zeros >= psk_speeds[psk_ctrl_config.speed_idx].value)
{
Psk_Modulator_SetState(PSK_MOD_ACTIVE);
}
}
else if (DigiModes_TxBufferHasData())
{
DigiModes_TxBufferRemove( &psk_state.tx_char, BPSK );
Psk_Modulator_SetState(PSK_MOD_ACTIVE);
if (psk_state.tx_char == 0x04) // EOT, stop tranmission
{
// we send from buffer, and nothing more is in the buffer
// request sending the trailing sequence
Psk_Modulator_SetState(PSK_MOD_POSTAMBLE);
}
else
{
// if all zeros have been sent, look for new
// input from input buffer
psk_state.tx_bits = Bpsk_FindCharReversed(psk_state.tx_char);
// reset counter for spacing zeros
psk_state.tx_zeros = 0;
// reset counter for trailing postamble (which conclude a transmission)
psk_state.tx_ones = 0;
}
}

if (Psk_Modulator_GetState() == PSK_MOD_POSTAMBLE)
{
// this is for generating trailing postamble if the
// input comes from a buffer or if we are asked to
// switch off,
// we do this for roughly a second, i.e. we simply use the rate as "timer"
if (psk_state.tx_ones < psk_speeds[psk_ctrl_config.speed_idx].value)
{
psk_state.tx_ones+=16;
psk_state.tx_bits = 0xffff; // we add 16 bits of postamble
// so we may send a few more postamble than request, but who cares...
}
else
{
Psk_Modulator_SetState(PSK_MOD_INACTIVE);
}
}
}

// we test the current bit. If it is a zero, and we have no more postamble to transmit
// we alternate the phase of our signal phase (180 degree shift)
if ((psk_state.tx_bits & 0x1) == 0 && psk_state.tx_ones == 0)
{
psk_state.tx_wave_sign_next *= -1;
}

// if it is a phase shift, which equals a zero to transmit or we transmit our last bit
if (psk_state.tx_wave_sign_next != psk_state.tx_wave_sign_current || Psk_Modulator_GetState() == PSK_MOD_INACTIVE)
{
// we have to shape the signal
psk_state.tx_win = true;
}
else
{
// it is a one and not the end, so we simply keep the full swing,
// i.e. a constant amplitude signal
psk_state.tx_win = false;
}

psk_state.tx_bits >>= 1; // remove "used" bit
}

// here we are in the middle of bit
// we move the next sign in, since it may indicate a phase shift
// in this case we are transmitting a zero
if (bit_middle(psk_state.tx_bit_phase))
{

psk_state.tx_wave_sign_current = psk_state.tx_wave_sign_next;

// if we are in the middle of a bit AND it is a zero bit
// we have to start our envelope from null
if (psk_state.tx_win)
{
Bpsk_ResetWin(); // we start the envelope from 0 to max
}
if (Psk_Modulator_GetState() == PSK_MOD_INACTIVE)
{
// now turn us off, we're done.
Psk_Modulator_SetState(PSK_MOD_OFF);
}
}

// if we are shaping the signal envelope
// we use the "slow" to generate our shape.
// we use abs so that we are getting only the gain
// not the phase from here
// otherwise we use the SAMPLE_MAX as coeff for constant amplitude
int32_t coeff = psk_state.tx_win ? abs(softdds_nextSample(&psk_bit_dds)) : SAMPLE_MAX;

// the bit length counter is incremented after each sample
// and wraps around after one bit length
psk_state.tx_bit_phase = (psk_state.tx_bit_phase + 1) % (psk_state.tx_bit_len / 2); // % 1576 == 1 bit length

retval = (coeff * psk_state.tx_wave_sign_current * softdds_nextSample(&psk_dds)) / SAMPLE_MAX;
}

return retval;
}

/**
* Returns the operational state of the PSK modulator
* @return current state
*/
psk_modulator_t Psk_Modulator_GetState()
{
return psk_state.tx_mod_state;
}

/**
* Change the state of the psk modulator to a new operational state
* If necessary, checks if state can be changed and executes code
* for the state transistion such as resetting variables to a known etc.
*
* @param newState
* @return the previous state
*/
psk_modulator_t Psk_Modulator_SetState(psk_modulator_t newState)
{
psk_modulator_t retval = psk_state.tx_mod_state;

switch(newState)
{
case PSK_MOD_PREAMBLE:
psk_state.tx_ones = 0;
psk_state.tx_win = true;
psk_state.tx_char = '\0';
psk_state.tx_bits = 0;
psk_state.tx_wave_sign_next = 1;
psk_state.tx_wave_sign_current = 1;
psk_state.tx_bit_phase = 0;
psk_state.tx_zeros = 0;
psk_state.tx_mod_state = newState;
break;
case PSK_MOD_OFF:
RadioManagement_Request_TxOff();
psk_state.tx_mod_state = newState;
break;
default:
psk_state.tx_mod_state = newState;
break;
}

return retval;
}}