two_pole_dc_pass/two_pole_7_8.c
Robin Clark afe551fe96 comment
2019-09-14 20:59:29 +01:00

375 lines
8.0 KiB
C

#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <math.h>
// Accuracy here matters.
// With a max 25k TDS (i.e. 16 bits input signal signed)
// this means 6 + 16 == 22.
// This fits within a 32 bit int
// and leaves ten bits of head room.
//
// For two pole the y0, y1, y2 registers must be 32 bit at least.
// The new rpi is 64 bit so these have had to have been deliberately set
// as int32_t to simulate the pic18 `long' type.
// The short int type on the PIC18 is `int'
//
#define BIN_FRACS 6
// this is a 64 bit machine (the pi)
//
int16_t /* squared version of LAG_7_8 */
two_pole_7_8 ( int16_t input ) {
static int32_t y1=0,y2=0, x1,x2;
int32_t * res;
int32_t y0;
int32_t x0 = input;
// x0 times 0.125
// the minus 3 divides by 8 : DOUBLE POLE
x0 <<= (BIN_FRACS-3) ; // now all calculations are done times BIN_FRACS^2
// this works stabley but not well WHY?
//y0 = x0 + y1-(y1>>3) - ((y2>>1) + (y2>>2) + (y2>>6));
// should be
//y0 = x0 + y1+y1-(y1>>2) - (y2>>1 + y2>>2 + y2>>6);
//
//
// OK this works well
// y0 = x0 + (14.0 / 8.0) * (double) y1 - (49.0/64.0) * (double) y2;
y0 = x0 +
// (14.0 / 8.0) * (double) y1
// this is 7/4
y1 + y1 - (y1>>2)
//
//
// - (49.0/64.0) * (double) y2;
//
- ( (y2>>1) + // half
(y2>>2) + // quarter
(y2>>6) ); // 64th
//
// y0 = x0/64 + (y1 * 7) / 4 + (y2*49)/64;
// see what happens when y2>>6 is left out. I theory d.c goes unstable
// and yes it does! 25AUG2019
// y0 = x0 + y1-(y1>>3) - (y2>>1 + y2>>2 /* + y2>>6*/);
y2 = y1;
y1 = y0;
x2 = x1;
x1 = x0;
//res = (short int *)&y0;
//res++;
//printf("y0=%X res should be %X res=%x\n",y0, y0>>16, res);
//
// the plus 3 divides by 8
return y0>>(BIN_FRACS+3); // divide back down for scaling and then divide by 8 filter gain // *res;
}
// Added zero guard. tried a pair of zeros near unit circle
// 7/8 in ADJ, i.e hyp = 1 so on unit circle.
//
int16_t /* squared version of LAG_7_8 */
two_pole_7_8_zg ( int16_t input ) { // with zero guard
static int32_t y1=0,y2=0, x1,x2,x3,x4,x5,x6,x7,x8;
int32_t * res;
int32_t y0;
int32_t x0 = input;
// x0 times 0.125
// the minus 3 divides by 8 : DOUBLE POLE
x0 <<= (BIN_FRACS-3) ; // now all calculations are done times BIN_FRACS^2
// this works stabley but not well WHY?
//y0 = x0 + y1-(y1>>3) - ((y2>>1) + (y2>>2) + (y2>>6));
// should be
//y0 = x0 + y1+y1-(y1>>2) - (y2>>1 + y2>>2 + y2>>6);
//
//
// OK this works well
// y0 = x0 + (14.0 / 8.0) * (double) y1 - (49.0/64.0) * (double) y2;
// (z-j)(z+j) zeros at half nyquist (Z^2 + 1) x0 + x2
y0 = //(x0>>1) + (x2>>1) +
(x0+x1+x2+x3) +
//(x0>>1) + (x0>>2) + (x0>>6) + (x2>>1) + // 49/64 * x0 + 1/2 * x2
// (14.0 / 8.0) * (double) y1
// this is 7/4
y1 + y1 - (y1>>2)
//
//
// - (49.0/64.0) * (double) y2;
//
- ( (y2>>1) + // half
(y2>>2) + // quarter
(y2>>6) ); // 64th
//
// y0 = x0/64 + (y1 * 7) / 4 + (y2*49)/64;
// see what happens when y2>>6 is left out. I theory d.c goes unstable
// and yes it does! 25AUG2019
// y0 = x0 + y1-(y1>>3) - (y2>>1 + y2>>2 /* + y2>>6*/);
y2 = y1;
y1 = y0;
x4 = x3;
x3 = x2;
x2 = x1;
x1 = x0;
//res = (short int *)&y0;
//res++;
//printf("y0=%X res should be %X res=%x\n",y0, y0>>16, res);
//
// the plus 3 divides by 8
return y0>>(BIN_FRACS+3); // divide back down for scaling and then divide by 8 filter gain // *res;
}
//
// At 20,000 TDS with 1500 noise this caused instability in the filter
// when BINFRACS was set to 9. As the input is not divided
// its already 8 bits (*256) high. Try BINFRACS at 2.
//
#define BIN_FRACS_15_16 2
// this is a 64 bit machine (the pi)
//
int16_t /* squared version of LAG_15_16 */
two_pole_15_16 ( int16_t input ) {
static int32_t y1=0,y2=0, x1, x2;
int32_t * res;
int32_t y0;
int32_t x0 = input;
x0 <<= (BIN_FRACS_15_16) ; // now all calculations are done times BIN_FRACS^2
y0 = x0 +
//
// this is 30/16 == 15/8
y1 + y1 - (y1>>3)
//
//
// - (49.0/64.0) * (double) y2;
//
;
//- ( (y2>>1) + // half
// (y2>>2) + // quarter
// (y2>>3) + // eighth
// (y2>>8) // 256th
// );
//
// try to do the shfts in a way effecient for the HYTEC PIC18 compiler
//
y2>>=1;
y0 -= y2;
y2>>=1;
y0 -= y2;
y2>>=1;
y0 -= y2;
y2>>=5;
y0 -= y2;
y2 = y1;
y1 = y0;
// gain of the filter is 256 ((1/16)^2) if x0 is allowed in without pre-dividing
//
y0 >>= 8;
return y0>>(BIN_FRACS_15_16); // divide back down for scaling and then divide by 8 filter gain // *res;
}
int zero_only_2 ( int input )
{
static int x0,x1,x2,x3,x4;
int res=1500*4;
// (z^2+1)^2 ZEROS AT HALF NYQUIST
// z^4 z^2 1
//res = input + 2*x2 + x4;
x4 = x3;
x3 = x2;
x2 = x1;
x1 = input;
return res/4;
}
int zero_only_3 ( int input )
{
static int x0,x1,x2,x3,x4;
static int x5,x6,x7,x8,x9;
int res=1500;;
// (Z+j)(Z-j) == (Z^2+1) // zero at nyquist
// (z^2+1)^3 ZEROS AT HALF NYQUIST
// z^6 z^4 2z^3 z^2 2*z 1
//res = input + x2 +2*x3 + x4 +2*x2 + x6;
// (Z^2 - 1)(Z+1) is zero at half nyquist and zero at nyquist
// z^3 +z^2 + z + 1
res = input + x1 + x2 + x3;
x8 = x7;
x7 = x6;
x6 = x5;
x5 = x4;
x4 = x3;
x3 = x2;
x2 = x1;
x1 = input;
return res/4;
}
int zero_only_4 ( int input )
{
static int x0,x1,x2,x3,x4;
static int x5,x6,x7,x8,x9;
int res=1500*16;
// (Z^2+1)^4 ZEROS AT HALF NYQUIST
// z^8 2z^6 2z^5 2z^4 4z^3 2z^2 2z^1 + 1
//res = input + 2*x2 +2*x3 + x4 + 4*x5 + 2*x6 + 2*x7 + x8;
// (Z+1)(Z-1 // zero at nyquist zero at half nyquist
// (Z^2 - 1)
//
x8 = x7;
x7 = x6;
x6 = x5;
x5 = x4;
x4 = x3;
x3 = x2;
x2 = x1;
x1 = input;
return res/16;
}
// 1/16 is 0.0625
//
// A double precision two pole filter could be used in a higher level
// to further smooth readings
#define DOUBLE_FILTER_PARAM 0.01
#define DOUBLE_FILTER_PARAM_LAG (1.0 - DOUBLE_FILTER_PARAM)
int16_t /* squared version of LAG 0.01 0.99 */
two_pole_double_low_pass ( int16_t input ) {
static double x0, y1, y2;
static double res;
x0 = input;
res = x0 * (DOUBLE_FILTER_PARAM * DOUBLE_FILTER_PARAM);
res += y1 * 2.0 * DOUBLE_FILTER_PARAM_LAG;
res -= y2 * (DOUBLE_FILTER_PARAM_LAG * DOUBLE_FILTER_PARAM_LAG);
y2 = y1;
y1 = res;
return (int16_t) res + 0.5;
}
// This was initially tested at 1500 TDS with \pm 500 noise
// Tests at 15000 with \pm 1500 noise at BINFRACS 9 caused instability in the two pole 15 16
// BINFRACS down to 2 for that filter.
// #define RAND_RANGE 500
// #define DC_TERM 1500
#define RAND_RANGE 500
#define DC_TERM 1000
int main () {
int i, zo2,zo3,zo4;
int16_t val,res, res34, res78, res78_2, rr, res_1516, tpdlp, tpdlp_1516;
for (i=0;i<1000;i++) {
val = sin ( (double)i*10.0 / (3.142 * 2.0) ) * 10.0 + DC_TERM ;
rr = rand() % (RAND_RANGE*2);
rr -= RAND_RANGE;
val += rr;
// fast sine
//val = sin ( ((double)i*10.0) / (3.142 * 2.0) ) * 10000;
res = two_pole_7_8 ( val );
res_1516 = two_pole_15_16 ( val );
zo2 = two_pole_7_8_zg(val); // zero_only_2 (val);
zo3 = zero_only_3 (val);
zo4 = zero_only_4 (val);
tpdlp = two_pole_double_low_pass ( val );
tpdlp_1516 = two_pole_double_low_pass (res_1516); // as fed by the yellow trace
res34 = (((res34<<2) - res34)>>2) + (val>>2);
res78 = (((res78<<3) - res78)>>3) + (val>>3);
res78_2 = (((res78_2<<3) - res78_2)>>3) + (res78>>3); // feed res78 into another should be the same as two pole
// 1 3 5 7 9 11 13 15 17 19 21
printf ("%d val %d res %d res34 %d res78 %d res78_2 %d res_1516 %d zo2 %d zo3 %d zo4 %d tpdlp_1516 %dEOL\n",
i, val,res, res34, res78, res78_2, res_1516, zo2, zo3, zo4, tpdlp_1516);
}
return 0;
}