wrote fsk modulator that just generates levels for driving an external VCO

git-svn-id: https://svn.code.sf.net/p/freetel/code@3393 01035d8c-6547-0410-b346-abe4f91aad63

diff --git a/codec2-dev/src/CMakeLists.txt b/codec2-dev/src/CMakeLists.txt
index ecd4981626a31e6843fd280c51e9660961fad82b..6fa49a3b0e06fa899fadc6a5c8ee11d6cb0cef52 100644 (file)
--- a/codec2-dev/src/CMakeLists.txt
+++ b/codec2-dev/src/CMakeLists.txt
@@ -311,6 +311,9 @@ target_link_libraries(freedv_rx ${CMAKE_REQUIRED_LIBRARIES} codec2)
 add_executable(fsk_mod fsk_mod.c)
 target_link_libraries(fsk_mod ${CMAKE_REQUIRED_LIBRARIES} codec2)
 
+add_executable(fsk_mod_ext_vco fsk_mod_ext_vco.c)
+target_link_libraries(fsk_mod_ext_vco)
+
 add_executable(fsk_demod fsk_demod.c modem_probe.c octave.c)
 target_link_libraries(fsk_demod ${CMAKE_REQUIRED_LIBRARIES} codec2)
 

diff --git a/codec2-dev/src/fsk_mod_ext_vco.c b/codec2-dev/src/fsk_mod_ext_vco.c
new file mode 100644 (file)
index 0000000..232da98
--- /dev/null
+++ b/codec2-dev/src/fsk_mod_ext_vco.c
@@ -0,0 +1,108 @@
+/*---------------------------------------------------------------------------*\
+
+  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 tranmsitter 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 <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+
+int main(int argc,char *argv[]){
+    int   os, m, i, bit_i, sym;
+    float d;
+    FILE *fin,*fout;
+    
+    if(argc<5){
+        fprintf(stderr,"usage: %s MbitsPerFSKsymbol OutputSamplesPerSymbol deviationPerlevel InputOneBitPerCharFile OutputVcoRawFile\n",argv[0]);
+        exit(1);
+    }
+    
+    /* Extract parameters */
+    m = atoi(argv[1]);
+    os = atoi(argv[2]);
+    d = atof(argv[3]);
+    
+    uint8_t tx_bits[m];
+    int16_t rawbuf[os];
+
+    if (strcmp(argv[4],"-")==0){
+        fin = stdin;
+    } else {
+        fin = fopen(argv[4],"r");
+    }
+       
+    if(strcmp(argv[5],"-")==0){
+        fout = stdout;
+    } else {
+        fout = fopen(argv[5],"w");
+    }
+    
+    /* Modulate m bits to levels to drive external VCO */
+
+    while( fread(tx_bits, sizeof(uint8_t), m, fin) == m ){
+
+        /* 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);
+
+        /* 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 */
+
+        float symf = sym;
+        float level = d*(symf - ((float)m-1)*0.5);
+        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(fin == stdin || fout == stdin){
+            fflush(fin);
+            fflush(fout);
+        }
+    }
+    
+    fclose(fin);
+    fclose(fout);
+
+    exit(0);
+}