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https://idyl.io repository for code examples
Hi!
I've modified your implementation a little bit to work with arbitrary bit counts both in integer/decimal parts of the number as well as in "PWM" value which I actually use to feed to the 12-bit DAC. I've used C, so:
fpm.h:
#ifndef FPM_FPM_H
#define FPM_FPM_H
#include <stdint.h>
#define DECIMAL_BITS 12u
typedef uint32_t ifloat;
#define int_to_ifloat(n) ((n) << DECIMAL_BITS)
#define ifloat_to_int(n) ((n) >> DECIMAL_BITS)
#define float_to_ifloat(n) ((uint32_t)((n) * (1u << DECIMAL_BITS)))
#define ifloat_to_float(n) (((float)(n)) / (float)(1u << DECIMAL_BITS))
static inline ifloat mul_ifloat(ifloat a, ifloat b) {
return (a * b) >> DECIMAL_BITS;
}
struct sin_wave {
ifloat value;
ifloat inverse_wave_len;
uint32_t wave_len;
uint32_t mod;
uint16_t bitval;
uint8_t mul;
};
struct sin_wave *create_sin_wave(uint32_t wave_duration, uint8_t bits);
void delete_sin_wave(struct sin_wave *wave);
void tick_sin_wave(struct sin_wave *wave);
#endif //FPM_FPM_H
fpm.c:
#include <stdlib.h>
#include "fpm.h"
static const ifloat ZERO = int_to_ifloat(0u);
static const ifloat ONE = int_to_ifloat(1u);
static const ifloat TWO = int_to_ifloat(2u);
static const ifloat THREE = int_to_ifloat(3u);
static const ifloat FOUR = int_to_ifloat(4u);
// f(x) = x^2 if x <= 1
// f(x) = -(x-2)^2 + 2 if 1 < x <= 3
// f(x) = (x-4)^2 otherwise
static ifloat quadratic_wave(const ifloat v) {
ifloat x = v;
if (x <= ONE) {
return mul_ifloat(x, x);
}
if (x <= THREE) {
x -= TWO;
x = mul_ifloat(x, x);
return ZERO - x + TWO;
}
x -= FOUR;
return mul_ifloat(x, x);
}
struct sin_wave *create_sin_wave(const uint32_t wave_duration, uint8_t bits) {
struct sin_wave* result = malloc(sizeof(struct sin_wave));
result->wave_len = wave_duration;
result->value = 0;
result->inverse_wave_len = float_to_ifloat(1.0f / wave_duration);
result->mod = 0xFFFFFFFF;
result->bitval = 0;
result->mul = (uint8_t) (bits - 1u);
tick_sin_wave(result);
return result;
}
void delete_sin_wave(struct sin_wave *wave) {
free(wave);
}
void tick_sin_wave(struct sin_wave *wave) {
if (++wave->mod >= wave->wave_len) {
wave->mod = 0;
}
wave->value = mul_ifloat(int_to_ifloat(wave->mod), wave->inverse_wave_len);
wave->value <<= 2u;
wave->value = quadratic_wave(wave->value);
wave->bitval = (uint16_t) ifloat_to_int(wave->value << wave->mul);
}
There are some hacks such as ticking during init, however by changing DECIMAL_BITS
define it is possible to change decimal resolution as well as produce values in different ranges. Also I was using timer interrupts to perform "ticks", so there is no need to call for millis()
.
Example of usage:
#include <stdio.h>
#include <math.h>
#include "fpm.h"
int main(int argc, char **argv) {
struct sin_wave *wave = create_sin_wave(100, 8);
for (uint32_t i = 0; i < 200; i++) {
tick_sin_wave(wave);
printf("%d,%d\n", i, wave->bitval);
}
delete_sin_wave(wave);
return 0;
}
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