Ab und zu braucht man eine Sinus-Tabelle in seinem Programm um aufwendigem Berechnen zur Laufzeit zu entgehen. Hierfür habe ich mir mal dieses kleine Tool geschrieben.
Compiliert wird es ganz einfach mit „gcc -lm sintab_generator.c -o sintab_generator“. Die Maths-Library ist die einzige Abhängigkeit hierfür, die aber schon in der glibc bzw. Standard-C-Library mit drin steckt.
„./sintab_generator –help“ listet alle Möglichkeiten auf.
Ein Beispiel für eine 8-Bit Tabelle, nur Positive Zahlen (Signal-Null liegt bei Amplitude/2 und nicht bei 0), Amplitude Max. 255, 128 Werte:
„./sintab_generator -d 16 -A 0xff -l 128 -c“
Diese Tabelle könnte so von einem DA Wandler am AVR ausgegeben werden. Ein Einfacher DA-Wandler wäre z.B. nur ein Portpin+RC-Glied mittels PWM.
/* simple generator for sine tables to include in c code * * (c) 2012 nils stec * * license: GPL * */ #include <stdio.h> #include <stdlib.h> #include <string.h> #include <inttypes.h> #include <sys/types.h> #include <math.h> #define DT_8 1 #define DT_16 2 #define DT_32 4 #define DT_DOUBLE 16 #define DT_SIGNED 0 #define DT_UNSIGNED 1 void help(); void gen_table(unsigned int len, unsigned int amplitude, int offset, int sign, int datatype, int comment); int main(int argc, char **argv) { int i; unsigned int len = 32; unsigned int amp = 0; int off = 0; int sign = DT_SIGNED; int datatype = DT_8; int comment = 0; int itemp; unsigned long int ultemp; long int ltemp; unsigned int calc_temp; for(i = 0; i < argc; i++) { if(!(strcmp(argv[i], "-u"))) { // only unsigned values sign = DT_UNSIGNED; } else if( (!(strcmp(argv[i], "-h"))) || (!(strcmp(argv[i], "--help"))) ) { help(); exit(0); } else if(!(strcmp(argv[i], "-c"))) { // add comment comment = 1; } else if(!(strcmp(argv[i], "-o"))) { // offset DEC if(argv[i+1] == NULL) { printf("\nyou'll need to give me an offset!\n\n"); exit(1); } ltemp = strtol(argv[i+1], NULL, 10); if(ltemp == 0) { printf("\nzero-offset not allowed!\n\n"); exit(1); } off = (int)ltemp; } else if(!(strcmp(argv[i], "-a"))) { // amplitude DEC if(argv[i+1] == NULL) { printf("\nyou'll need to give me max. amplitude!\n\n"); exit(1); } ltemp = strtol(argv[i+1], NULL, 10); if(ltemp < 2) { printf("\namplitude negative or too small!\n\n"); exit(1); } amp = (unsigned int)ltemp; } else if(!(strcmp(argv[i], "-O"))) { // offset HEX if(argv[i+1] == NULL) { printf("\nyou'll need to give me an offset in hex!\n\n"); exit(1); } ltemp = strtol(argv[i+1], NULL, 16); if(ltemp == 0) { printf("\nzero-offset not allowed!\n\n"); exit(1); } off = (int)ltemp; } else if(!(strcmp(argv[i], "-A"))) { // amplitude HEX if(argv[i+1] == NULL) { printf("\nyou'll need to give me max. amplitude in hex!\n\n"); exit(1); } ltemp = strtol(argv[i+1], NULL, 16); if(ltemp < 2) { printf("\namplitude negative or too small!\n\n"); exit(1); } amp = (unsigned int)ltemp; } else if(!(strcmp(argv[i], "-l"))) { // length if(argv[i+1] == NULL) { printf("\nyou'll need to give me the length!\n\n"); exit(1); } ltemp = strtol(argv[i+1], NULL, 10); if(ltemp < 2) { printf("\ntoo short!\n\n"); exit(1); } if((ltemp%2) != 0) { printf("\nlen has to be a power of 2!\n\n"); exit(1); } len = (unsigned int)ltemp; } else if(!(strcmp(argv[i], "-d"))) { // datatype if(argv[i+1] == NULL) { printf("\nyou'll need to give me a datatype!\n\n"); exit(1); } ultemp = strtoul(argv[i+1], NULL, 10); itemp = (int)ultemp; switch(itemp) { case 8: datatype = DT_8; break; case 16: datatype = DT_16; break; case 32: datatype = DT_32; break; default: if(strcmp(argv[i+1], "double") == 0) { datatype = DT_DOUBLE; } else { printf("\nwrong datatype!\n\n"); help(); exit(1); } break; } } } printf("\n"); switch(datatype) { case DT_8: ultemp = 0xff; ltemp = 0xff; break; case DT_16: ultemp = 0xffff; ltemp = 0xffff; break; case DT_32: ultemp = 0xffffffff; ltemp = 0xffffffff; break; case DT_DOUBLE: break; } if(datatype != DT_DOUBLE) { if(off < 0) calc_temp = (unsigned int)off * -1; else calc_temp = (unsigned int)off; if((calc_temp+amp) > ultemp) { printf("\ndatatype too small to hold your sine!\n\n"); exit(-1); } } gen_table(len, amp, off, sign, datatype, comment); return 0; } void help() { printf("c sine table generator 0.01 [(c) 2012, nils stec]\n\n"); printf(" -d 8/16/32/double datatypes: int8_t,int16_t,int32_t,double\n"); printf(" -u force unsigned values (signal zero is at max_amplitude/2)\n"); printf(" -o offset offset DECIMAL\n"); printf(" -O offset offset HEX\n"); printf(" -a max_amplitude max amplitude DECIMAL\n"); printf(" -A max_amplitude max amplitude HEX\n"); printf(" -l len length\n"); printf(" -c add comment\n"); return; } void gen_table(unsigned int len, unsigned int amplitude, int offset, int sign, int datatype, int comment) { double sine; int n, i; uint32_t table_entry; if(sign == DT_UNSIGNED) { // if we want unsigned data, we have to pull our sine higher than zero while((int)(offset-amplitude)<0) offset++; } if(comment) { printf("/* sine table, "); if(datatype != DT_DOUBLE) { printf("max amplitude %d, ", amplitude); printf("offset %d, ", offset); } printf("%d entries, size in memory: %dbytes */\n", len, datatype*len); } if(datatype != DT_DOUBLE) { if(sign==DT_UNSIGNED) printf("u"); switch(datatype) { case DT_8: printf("int8_t sine_table[%d] = {\n", len); break; case DT_16: printf("int16_t sine_table[%d] = {\n", len); break; case DT_32: printf("int32_t sine_table[%d] = {\n", len); break; } } else printf("double sine_table[%d] = {\n", len); n = 0; while(n < len) { printf(""); for(i = 0; i < 8; i++) { sine = sin(2.0*M_PI*n/len); switch(datatype) { case DT_DOUBLE: printf("%f", sine); break; default: table_entry = (sine*(double)amplitude)+offset; printf("%d", table_entry); break; } n++; if(n < len) printf(", "); } printf("\n"); } printf("};\n\n"); }
Krumeltee 