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13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
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18 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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21 * library without restriction. Specifically, if other files instantiate
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26 * invalidate any other reasons why the executable file might be covered by
27 * the GNU General Public License.
29 * Copyright 2008 Develer S.r.l. (http://www.develer.com/)
33 * \brief AFSK1200 modem.
36 * \author Francesco Sacchi <asterix@develer.com>
42 #include "cfg/cfg_afsk.h"
43 #include "hw/hw_afsk.h"
45 #include <drv/timer.h>
47 #include <cfg/module.h>
49 #include <cpu/power.h>
50 #include <struct/fifobuf.h>
52 #include <string.h> /* memset */
54 // Demodulator constants
55 #define SAMPLERATE 9600
58 #define SAMPLEPERBIT (SAMPLERATE / BITRATE)
62 #define PHASE_MAX (SAMPLEPERBIT * PHASE_BIT)
63 #define PHASE_THRES (PHASE_MAX / 2) // - PHASE_BIT / 2)
65 // Modulator constants
66 #define MARK_FREQ 1200
67 #define MARK_INC (uint16_t)(DIV_ROUND(SIN_LEN * (uint32_t)MARK_FREQ, CONFIG_AFSK_DAC_SAMPLERATE))
69 #define SPACE_FREQ 2200
70 #define SPACE_INC (uint16_t)(DIV_ROUND(SIN_LEN * (uint32_t)SPACE_FREQ, CONFIG_AFSK_DAC_SAMPLERATE))
72 //Ensure sample rate is a multiple of bit rate
73 STATIC_ASSERT(!(CONFIG_AFSK_DAC_SAMPLERATE % BITRATE));
75 #define DAC_SAMPLEPERBIT (CONFIG_AFSK_DAC_SAMPLERATE / BITRATE)
78 /** Current sample of bit for output data. */
79 static uint8_t sample_count;
81 /** Current character to be modulated */
82 static uint8_t curr_out;
84 /** Mask of current modulated bit */
85 static uint8_t tx_bit;
87 /** True if bit stuff is allowed, false otherwise */
88 static bool bit_stuff;
90 /** Counter for bit stuffing */
91 static uint8_t stuff_cnt;
94 * Sine table for the first quarter of wave.
95 * The rest of the wave is computed from this first quarter.
96 * This table is used to generate the modulated data.
98 static const uint8_t sin_table[] =
101 128, 129, 131, 132, 134, 135, 137, 138, 140, 142, 143, 145, 146, 148, 149, 151,
102 152, 154, 155, 157, 158, 160, 162, 163, 165, 166, 167, 169, 170, 172, 173, 175,
103 176, 178, 179, 181, 182, 183, 185, 186, 188, 189, 190, 192, 193, 194, 196, 197,
104 198, 200, 201, 202, 203, 205, 206, 207, 208, 210, 211, 212, 213, 214, 215, 217,
105 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233,
106 234, 234, 235, 236, 237, 238, 238, 239, 240, 241, 241, 242, 243, 243, 244, 245,
107 245, 246, 246, 247, 248, 248, 249, 249, 250, 250, 250, 251, 251, 252, 252, 252,
108 253, 253, 253, 253, 254, 254, 254, 254, 254, 255, 255, 255, 255, 255, 255, 255,
111 #define SIN_LEN 512 ///< Full wave length
113 STATIC_ASSERT(sizeof(sin_table) == SIN_LEN / 4);
116 * DDS phase accumulator for generating modulated data.
118 static uint16_t phase_acc;
120 /** Current phase increment for current modulated bit */
121 static uint16_t phase_inc = MARK_INC;
125 * Given the index, this function computes the correct sine sample
126 * based only on the first quarter of wave.
128 INLINE uint8_t sin_sample(uint16_t idx)
130 ASSERT(idx < SIN_LEN);
131 uint16_t new_idx = idx % (SIN_LEN / 2);
132 new_idx = (new_idx >= (SIN_LEN / 4)) ? (SIN_LEN / 2 - new_idx - 1) : new_idx;
133 return (idx >= (SIN_LEN / 2)) ? (255 - sin_table[new_idx]) : sin_table[new_idx];
137 static FIFOBuffer delay_fifo;
140 * Buffer for delay FIFO.
141 * The 1 is added because the FIFO macros need
142 * 1 byte more to handle a buffer (SAMPLEPERBIT / 2) bytes long.
144 static int8_t delay_buf[SAMPLEPERBIT / 2 + 1];
146 static FIFOBuffer rx_fifo;
147 static uint8_t rx_buf[CONFIG_AFSK_RX_BUFLEN];
149 static FIFOBuffer tx_fifo;
150 static uint8_t tx_buf[CONFIG_AFSK_TX_BUFLEN];
152 static int16_t iir_x[2];
153 static int16_t iir_y[2];
154 static uint8_t sampled_bits;
155 static uint8_t found_bits;
156 static uint8_t demod_bits;
157 static int8_t curr_phase;
159 static bool hdlc_rxstart;
160 static uint8_t hdlc_currchar;
161 static uint8_t hdlc_bit_idx;
163 #define BIT_DIFFER(bitline1, bitline2) (((bitline1) ^ (bitline2)) & 0x01)
164 #define EDGE_FOUND(bitline) BIT_DIFFER((bitline), (bitline) >> 1)
166 static void hdlc_parse(bool bit)
169 demod_bits |= bit ? 1 : 0;
172 if (demod_bits == HDLC_FLAG)
174 if (!fifo_isfull(&rx_fifo))
176 fifo_push(&rx_fifo, HDLC_FLAG);
180 hdlc_rxstart = false;
188 if ((demod_bits & HDLC_RESET) == HDLC_RESET)
190 hdlc_rxstart = false;
198 if ((demod_bits & 0x3f) == 0x3e)
201 if (demod_bits & 0x01)
202 hdlc_currchar |= 0x80;
204 if (++hdlc_bit_idx >= 8)
206 if ((hdlc_currchar == HDLC_FLAG
207 || hdlc_currchar == HDLC_RESET
208 || hdlc_currchar == AX25_ESC))
210 if (!fifo_isfull(&rx_fifo))
211 fifo_push(&rx_fifo, AX25_ESC);
213 hdlc_rxstart = false;
216 if (!fifo_isfull(&rx_fifo))
217 fifo_push(&rx_fifo, hdlc_currchar);
219 hdlc_rxstart = false;
229 DEFINE_AFSK_ADC_ISR()
232 int8_t curr_sample = AFSK_READ_ADC();
235 * Frequency discriminator and LP IIR filter.
236 * This filter is designed to work
237 * at the given sample rate and bit rate.
239 STATIC_ASSERT(SAMPLERATE == 9600);
240 STATIC_ASSERT(BITRATE == 1200);
243 * Frequency discrimination is achieved by simply multiplying
244 * the sample with a delayed sample of (samples per bit) / 2.
245 * Then the signal is lowpass filtered with a first order,
246 * 600 Hz filter. The filter implementation is selectable
247 * through the CONFIG_AFSK_FILTER config variable.
252 #if (CONFIG_AFSK_FILTER == AFSK_BUTTERWORTH) || (CONFIG_AFSK_FILTER == AFSK_CHEBYSHEV)
253 iir_x[1] = ((int8_t)fifo_pop(&delay_fifo) * curr_sample) >> 2;
255 #error Filter type not found!
260 #if CONFIG_AFSK_FILTER == AFSK_BUTTERWORTH
262 * This strange sum + shift is an optimization for iir_y[0] * 0.668.
263 * iir * 0.668 ~= (iir * 21) / 32 =
264 * = (iir * 16) / 32 + (iir * 4) / 32 + iir / 32 =
265 * = iir / 2 + iir / 8 + iir / 32 =
266 * = iir >> 1 + iir >> 3 + iir >> 5
268 iir_y[1] = iir_x[0] + iir_x[1] + (iir_y[0] >> 1) + (iir_y[0] >> 3) + (iir_y[0] >> 5);
269 #elif CONFIG_AFSK_FILTER == AFSK_CHEBYSHEV
271 * This should be (iir_y[0] * 0.438) but
272 * (iir_y[0] >> 1) is a faster approximation :-)
274 iir_y[1] = iir_x[0] + iir_x[1] + (iir_y[0] >> 1);
277 /* Save this sampled bit in a delay line */
279 sampled_bits |= (iir_y[1] > 0) ? 1 : 0;
281 /* Store current ADC sample in the delay_fifo */
282 fifo_push(&delay_fifo, curr_sample);
284 /* If there is an edge, adjust phase sampling */
285 if (EDGE_FOUND(sampled_bits))
287 if (curr_phase < PHASE_THRES)
288 curr_phase += PHASE_INC;
290 curr_phase -= PHASE_INC;
292 curr_phase += PHASE_BIT;
295 if (curr_phase >= PHASE_MAX)
297 curr_phase %= PHASE_MAX;
299 /* Shift 1 position in the shift register of the found bits */
303 * TODO: maybe a better algorithm to find the sample bit
304 * other than reading the last one.
306 found_bits |= sampled_bits & 1;
309 * NRZI coding: if 2 consecutive bits have the same value
310 * a 1 is received, otherwise it's a 0.
312 hdlc_parse(!EDGE_FOUND(found_bits));
320 /* True while modem sends data */
321 static volatile bool sending;
323 static void afsk_txStart(void)
327 phase_inc = MARK_INC;
331 AFSK_DAC_IRQ_START();
335 #define BIT_STUFF_LEN 5
337 #define SWITCH_TONE(inc) (((inc) == MARK_INC) ? SPACE_INC : MARK_INC)
339 DEFINE_AFSK_DAC_ISR()
341 /* Check if we are at a start of a sample cycle */
342 if (sample_count == 0)
346 /* We have just finished transimitting a char, get a new one. */
347 if (fifo_isempty(&tx_fifo))
357 * If we have just finished sending an unstuffed byte,
358 * reset bitstuff counter.
364 curr_out = fifo_pop(&tx_fifo);
366 /* Handle char escape */
367 if (curr_out == AX25_ESC)
369 if (fifo_isempty(&tx_fifo))
377 curr_out = fifo_pop(&tx_fifo);
379 else if (curr_out == HDLC_FLAG || curr_out == HDLC_RESET)
380 /* If these chars are not escaped disable bit stuffing */
383 /* Start with LSB mask */
387 /* check for bit stuffing */
388 if (bit_stuff && stuff_cnt >= BIT_STUFF_LEN)
390 /* If there are more than 5 ones in a row insert a 0 */
393 phase_inc = SWITCH_TONE(phase_inc);
398 * NRZI: if we want to transmit a 1 the modulated frequency will stay
399 * unchanged; with a 0, there will be a change in the tone.
401 if (curr_out & tx_bit)
405 * - Stay on the previous tone
406 * - Increace bit stuff count
414 * - Reset bit stuff count
418 phase_inc = SWITCH_TONE(phase_inc);
421 /* Go to the next bit */
424 sample_count = DAC_SAMPLEPERBIT;
427 /* Get new sample and put it out on the DAC */
428 phase_acc += phase_inc;
429 phase_acc %= SIN_LEN;
431 AFSK_SET_DAC(sin_sample(phase_acc));
437 static size_t afsk_read(UNUSED_ARG(KFile *, fd), void *_buf, size_t size)
439 uint8_t *buf = (uint8_t *)_buf;
441 #if CONFIG_AFSK_RXTIMEOUT == 0
442 while (size-- && !fifo_isempty_locked(&rx_fifo))
447 #if CONFIG_AFSK_RXTIMEOUT != -1
448 ticks_t start = timer_clock();
451 while (fifo_isempty_locked(&rx_fifo));
454 #if CONFIG_AFSK_RXTIMEOUT != -1
455 if (timer_clock() - start > ms_to_ticks(CONFIG_AFSK_RXTIMEOUT))
456 return buf - (uint8_t *)_buf;
460 *buf++ = fifo_pop_locked(&rx_fifo);
463 return buf - (uint8_t *)_buf;
466 static size_t afsk_write(UNUSED_ARG(KFile *, fd), const void *_buf, size_t size)
468 const uint8_t *buf = (const uint8_t *)_buf;
472 while (fifo_isfull_locked(&tx_fifo))
475 fifo_push_locked(&tx_fifo, *buf++);
479 return buf - (const uint8_t *)_buf;
482 static int afsk_flush(UNUSED_ARG(KFile *, fd))
490 void afsk_init(Afsk *af)
492 #if CONFIG_AFSK_RXTIMEOUT != -1
496 fifo_init(&delay_fifo, (uint8_t *)delay_buf, sizeof(delay_buf));
497 fifo_init(&rx_fifo, rx_buf, sizeof(rx_buf));
499 /* Fill sample FIFO with 0 */
500 for (int i = 0; i < SAMPLEPERBIT / 2; i++)
501 fifo_push(&delay_fifo, 0);
503 fifo_init(&tx_fifo, tx_buf, sizeof(tx_buf));
507 kprintf("MARK_INC %d, SPACE_INC %d\n", MARK_INC, SPACE_INC);
509 memset(af, 0, sizeof(*af));
510 DB(af->fd._type = KFT_AFSK);
511 af->fd.write = afsk_write;
512 af->fd.read = afsk_read;
513 af->fd.flush = afsk_flush;