2014-04-02 18:17:23 +00:00
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/*
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PiFmRds - FM/RDS transmitter for the Raspberry Pi
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Copyright (C) 2014 Christophe Jacquet, F8FTK
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See https://github.com/ChristopheJacquet/PiFmRds
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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2014-03-31 22:03:10 +00:00
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#include <stdint.h>
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#include <string.h>
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#include <stdio.h>
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2014-06-22 16:58:52 +00:00
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#include <time.h>
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#include <stdlib.h>
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2014-03-31 22:03:10 +00:00
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#include "waveforms.h"
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2014-04-06 14:18:15 +00:00
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#define RT_LENGTH 64
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#define PS_LENGTH 8
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#define GROUP_LENGTH 4
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struct {
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char ps[PS_LENGTH];
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char rt[RT_LENGTH];
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2014-03-31 22:03:10 +00:00
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uint16_t pi;
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} rds_params;
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/* The RDS error-detection code generator polynomial is
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x^10 + x^8 + x^7 + x^5 + x^4 + x^3 + x^0
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*/
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#define POLY 0x1B9
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#define POLY_DEG 10
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#define MSB_BIT 0x8000
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#define BLOCK_SIZE 16
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#define BITS_PER_GROUP (GROUP_LENGTH * (BLOCK_SIZE+POLY_DEG))
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#define SAMPLES_PER_BIT 192
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#define FILTER_SIZE (sizeof(waveform_biphase)/sizeof(float))
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#define SAMPLE_BUFFER_SIZE (SAMPLES_PER_BIT + FILTER_SIZE)
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uint16_t offset_words[] = {0x0FC, 0x198, 0x168, 0x1B4};
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// We don't handle offset word C' here for the sake of simplicity
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/* Classical CRC computation */
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uint16_t crc(uint16_t block) {
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uint16_t crc = 0;
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for(int j=0; j<BLOCK_SIZE; j++) {
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int bit = (block & MSB_BIT) != 0;
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block <<= 1;
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int msb = (crc >> (POLY_DEG-1)) & 1;
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crc <<= 1;
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if((msb ^ bit) != 0) {
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crc = crc ^ POLY;
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}
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}
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return crc;
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}
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2014-06-22 16:58:52 +00:00
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/* Possibly generates a CT (clock time) group if the minute has just changed
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Returns 1 if the CT group was generated, 0 otherwise
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*/
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int get_rds_ct_group(uint16_t *blocks) {
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static int latest_minutes = -1;
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// Check time
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time_t now;
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struct tm *utc;
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now = time (NULL);
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utc = gmtime (&now);
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if(utc->tm_min != latest_minutes) {
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// Generate CT group
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latest_minutes = utc->tm_min;
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int l = utc->tm_mon <= 1 ? 1 : 0;
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int mjd = 14956 + utc->tm_mday +
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(int)((utc->tm_year - l) * 365.25) +
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(int)((utc->tm_mon + 2 + l*12) * 30.6001);
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blocks[1] = 0x4000 | (mjd>>15);
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blocks[2] = (mjd<<1) | (utc->tm_hour>>4);
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blocks[3] = (utc->tm_hour & 0xF)<<12 | utc->tm_min<<6;
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utc = localtime(&now);
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int offset = utc->tm_gmtoff / (30 * 60);
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blocks[3] |= abs(offset);
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if(offset < 0) blocks[3] |= 0x20;
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2014-06-22 20:35:27 +00:00
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//printf("Generated CT: %04X %04X %04X\n", blocks[1], blocks[2], blocks[3]);
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return 1;
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} else return 0;
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}
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/* Creates an RDS group. This generates sequences of the form 0B, 0B, 0B, 0B, 2A, etc.
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The pattern is of length 5, the variable 'state' keeps track of where we are in the
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pattern. 'ps_state' and 'rt_state' keep track of where we are in the PS (0B) sequence
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or RT (2A) sequence, respectively.
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*/
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void get_rds_group(int *buffer) {
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static int state = 0;
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static int ps_state = 0;
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static int rt_state = 0;
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uint16_t blocks[GROUP_LENGTH] = {rds_params.pi, 0, 0, 0};
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// Generate block content
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if(! get_rds_ct_group(blocks)) { // CT (clock time) has priority on other group types
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if(state < 4) {
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blocks[1] = 0x0000 | ps_state;
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blocks[2] = 0xCDCD; // no AF
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blocks[3] = rds_params.ps[ps_state*2]<<8 | rds_params.ps[ps_state*2+1];
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ps_state++;
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if(ps_state >= 4) ps_state = 0;
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} else { // state == 5
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blocks[1] = 0x2000 | rt_state;
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blocks[2] = rds_params.rt[rt_state*4+0]<<8 | rds_params.rt[rt_state*4+1];
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blocks[3] = rds_params.rt[rt_state*4+2]<<8 | rds_params.rt[rt_state*4+3];
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rt_state++;
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if(rt_state >= 16) rt_state = 0;
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}
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2014-06-22 16:58:52 +00:00
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state++;
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if(state >= 5) state = 0;
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}
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// Calculate the checkword for each block and emit the bits
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for(int i=0; i<GROUP_LENGTH; i++) {
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uint16_t block = blocks[i];
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uint16_t check = crc(block) ^ offset_words[i];
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for(int j=0; j<BLOCK_SIZE; j++) {
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*buffer++ = ((block & (1<<(BLOCK_SIZE-1))) != 0);
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block <<= 1;
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}
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for(int j=0; j<POLY_DEG; j++) {
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*buffer++= ((check & (1<<(POLY_DEG-1))) != 0);
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check <<= 1;
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}
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}
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}
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2014-04-02 18:17:23 +00:00
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/* Get a number of RDS samples. This generates the envelope of the waveform using
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pre-generated elementary waveform samples, and then it amplitude-modulates the
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envelope with a 57 kHz carrier, which is very efficient as 57 kHz is 4 times the
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sample frequency we are working at (228 kHz).
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*/
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void get_rds_samples(float *buffer, int count) {
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static int bit_buffer[BITS_PER_GROUP];
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static int bit_pos = BITS_PER_GROUP;
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static float sample_buffer[SAMPLE_BUFFER_SIZE] = {0};
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2014-04-02 18:17:23 +00:00
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static int prev_output = 0;
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static int cur_output = 0;
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static int cur_bit = 0;
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static int sample_count = SAMPLES_PER_BIT;
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static int inverting = 0;
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static int phase = 0;
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static int in_sample_index = 0;
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static int out_sample_index = SAMPLE_BUFFER_SIZE-1;
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for(int i=0; i<count; i++) {
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if(sample_count >= SAMPLES_PER_BIT) {
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if(bit_pos >= BITS_PER_GROUP) {
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get_rds_group(bit_buffer);
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bit_pos = 0;
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}
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2014-04-02 18:17:23 +00:00
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// do differential encoding
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cur_bit = bit_buffer[bit_pos];
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prev_output = cur_output;
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cur_output = prev_output ^ cur_bit;
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2014-04-05 17:36:06 +00:00
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inverting = (cur_output == 1);
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2014-04-04 23:26:45 +00:00
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float *src = waveform_biphase;
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int idx = in_sample_index;
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2014-04-04 23:26:45 +00:00
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for(int j=0; j<FILTER_SIZE; j++) {
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float val = (*src++);
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if(inverting) val = -val;
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sample_buffer[idx++] += val;
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if(idx >= SAMPLE_BUFFER_SIZE) idx = 0;
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}
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2014-04-04 23:26:45 +00:00
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in_sample_index += SAMPLES_PER_BIT;
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if(in_sample_index >= SAMPLE_BUFFER_SIZE) in_sample_index -= SAMPLE_BUFFER_SIZE;
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bit_pos++;
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sample_count = 0;
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}
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2014-04-05 18:02:34 +00:00
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float sample = sample_buffer[out_sample_index];
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sample_buffer[out_sample_index] = 0;
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out_sample_index++;
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2014-04-05 17:36:06 +00:00
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if(out_sample_index >= SAMPLE_BUFFER_SIZE) out_sample_index = 0;
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2014-04-02 18:17:23 +00:00
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2014-04-05 18:02:34 +00:00
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2014-04-02 18:17:23 +00:00
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// modulate at 57 kHz
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// use phase for this
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switch(phase) {
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case 0:
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case 2: sample = 0; break;
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case 1: break;
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case 3: sample = -sample; break;
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}
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phase++;
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if(phase >= 4) phase = 0;
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*buffer++ = sample;
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sample_count++;
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}
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}
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2014-04-06 14:18:15 +00:00
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void set_rds_pi(uint16_t pi_code) {
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2014-04-02 20:48:41 +00:00
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rds_params.pi = pi_code;
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2014-04-02 20:48:41 +00:00
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}
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2014-04-06 14:18:15 +00:00
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void set_rds_rt(char *rt) {
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strncpy(rds_params.rt, rt, 64);
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2014-04-06 16:44:25 +00:00
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for(int i=0; i<64; i++) {
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if(rds_params.rt[i] == 0) rds_params.rt[i] = 32;
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}
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2014-04-06 14:18:15 +00:00
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}
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void set_rds_ps(char *ps) {
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strncpy(rds_params.ps, ps, 8);
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2014-04-06 16:44:25 +00:00
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for(int i=0; i<8; i++) {
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if(rds_params.ps[i] == 0) rds_params.ps[i] = 32;
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}
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2014-04-06 14:18:15 +00:00
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}
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