1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
|
/*---------------------------------------------------------------------------*\
FILE........: fsk_mod_ext_vco.c
AUTHOR......: David Rowe
DATE CREATED: Feb 2018
Converts a stream of bits to mFSK raw file of "levels" suitable for
driving an external VCO, e.g. legacy FM transmitter in data mode.
\*---------------------------------------------------------------------------*/
/*
Copyright (C) 2018 David Rowe
All rights reserved.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License version 2.1, as
published by the Free Software Foundation. This program is
distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#include <assert.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#define OVERSAMPLE 100
int main(int argc,char *argv[]){
int os, m, log2m, i, bit_i, sym, legacy_mode, rpitx_mode;
float d;
double shiftHz, symbolRateHz;
uint32_t time_sample;
FILE *fin,*fout;
if(argc<5){
fprintf(stderr, "usage: %s InputOneBitPerCharFile OutputVcoRawFile MbitsPerFSKsymbol\n",argv[0]);
fprintf(stderr, "[--legacy OutputSamplesPerSymbol deviationPerlevel]\n");
fprintf(stderr, "[--rpitx ShiftHz SymbolRateHz\n]");
exit(1);
}
/* Extract parameters */
if (strcmp(argv[1],"-")==0){
fin = stdin;
} else {
fin = fopen(argv[1],"r");
}
if (strcmp(argv[2],"-")==0){
fout = stdout;
} else {
fout = fopen(argv[2],"w");
}
m = atoi(argv[3]); log2m = log2(m);
printf("log2m: %d\n", log2m);
legacy_mode = rpitx_mode = os = 0;
if (!strcmp(argv[4],"--legacy")) {
os = atoi(argv[5]);
d = atof(argv[6]);
legacy_mode = 1;
}
if (!strcmp(argv[4],"--rpitx")) {
shiftHz = atof(argv[5]);
symbolRateHz = atof(argv[6]);
rpitx_mode = 1;
time_sample = 1E9/symbolRateHz;
fprintf(stderr, "time_sample: %d\n", time_sample);
}
assert(legacy_mode || rpitx_mode);
fprintf(stderr, "legacy_mode: %d rpitx_mode: %d\n", legacy_mode, rpitx_mode);
uint8_t tx_bits[log2m];
int16_t rawbuf[os];
/* Modulate m bits to levels to drive external VCO */
while( fread(tx_bits, sizeof(uint8_t), log2m, fin) == log2m ){
/* generate the symbol number from the bit stream,
e.g. 0,1 for 2FSK, 0,1,2,3 for 4FSK */
sym = bit_i = 0;
for( i=m; i>>=1; ){
//fprintf(stderr, "tx_bits[%d] = %d\n", i, tx_bits[bit_i]);
uint8_t bit = tx_bits[bit_i];
bit = (bit==1)?1:0;
sym = (sym<<1)|bit;
bit_i++;
}
//fprintf(stderr, "sym = %d\n", sym);
if (legacy_mode) {
/* map 'sym' to VCO drive signal symmetrically about 0,
separate tones by constant "d" */
/* 2 FSK -d/2, +d/2 */
/* 4 FSK -3*d/2, -d/2, +d/2, 3*d/2 */
/* note: drive is inverted, a higher tone drives VCO voltage lower */
float symf = sym;
float level = d*(((float)m-1)*0.5 - symf);
assert(level <= 32767.0);
assert(level >= -32768.0);
short level_short = (short)level;
//fprintf(stderr, "level = %f level_short = %d\n\n", level, level_short);
for(i=0; i<os; i++) {
rawbuf[i] = level_short;
}
fwrite(rawbuf, sizeof(int16_t), os, fout);
}
if (rpitx_mode) {
short frequencyHz;
frequencyHz = shiftHz*(sym+1);
fwrite(&frequencyHz, sizeof(short), 1, fout);
}
if(fout == stdout){
fflush(fout);
}
}
fclose(fin);
fclose(fout);
exit(0);
}
|
