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Fix timedomain transform (based on acd944d5fa by @erikkaashoek )

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cho45 2019-09-21 22:20:08 +09:00
parent e89c9bd6a7
commit 1120d5c33b
4 changed files with 70 additions and 45 deletions
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76
fft.h
View file

@ -26,8 +26,8 @@
#include <math.h> #include <math.h>
#include <stdint.h> #include <stdint.h>
static uint8_t reverse_bits(uint8_t x, int n) { static uint16_t reverse_bits(uint16_t x, int n) {
uint8_t result = 0; uint16_t result = 0;
for (int i = 0; i < n; i++, x >>= 1) for (int i = 0; i < n; i++, x >>= 1)
result = (result << 1) | (x & 1U); result = (result << 1) | (x & 1U);
return result; return result;
@ -36,38 +36,50 @@ static uint8_t reverse_bits(uint8_t x, int n) {
static const float sin_table[] = { static const float sin_table[] = {
/* /*
* float has about 7.2 digits of precision * float has about 7.2 digits of precision
for (uint8_t i = 0; i < 96; i++) { for (uint8_t i = 0; i < FFT_SIZE - (FFT_SIZE / 4); i++) {
printf("% .8f,%c", sin(2 * M_PI * i / n), i % 8 == 7 ? '\n' : ' '); printf("% .8f,%c", sin(2 * M_PI * i / FFT_SIZE), i % 8 == 7 ? '\n' : ' ');
} }
*/ */
0.00000000, 0.04906767, 0.09801714, 0.14673047, 0.19509032, 0.24298018, 0.29028468, 0.33688985, 0.00000000, 0.02454123, 0.04906767, 0.07356456, 0.09801714, 0.12241068, 0.14673047, 0.17096189,
0.38268343, 0.42755509, 0.47139674, 0.51410274, 0.55557023, 0.59569930, 0.63439328, 0.67155895, 0.19509032, 0.21910124, 0.24298018, 0.26671276, 0.29028468, 0.31368174, 0.33688985, 0.35989504,
0.70710678, 0.74095113, 0.77301045, 0.80320753, 0.83146961, 0.85772861, 0.88192126, 0.90398929, 0.38268343, 0.40524131, 0.42755509, 0.44961133, 0.47139674, 0.49289819, 0.51410274, 0.53499762,
0.92387953, 0.94154407, 0.95694034, 0.97003125, 0.98078528, 0.98917651, 0.99518473, 0.99879546, 0.55557023, 0.57580819, 0.59569930, 0.61523159, 0.63439328, 0.65317284, 0.67155895, 0.68954054,
1.00000000, 0.99879546, 0.99518473, 0.98917651, 0.98078528, 0.97003125, 0.95694034, 0.94154407, 0.70710678, 0.72424708, 0.74095113, 0.75720885, 0.77301045, 0.78834643, 0.80320753, 0.81758481,
0.92387953, 0.90398929, 0.88192126, 0.85772861, 0.83146961, 0.80320753, 0.77301045, 0.74095113, 0.83146961, 0.84485357, 0.85772861, 0.87008699, 0.88192126, 0.89322430, 0.90398929, 0.91420976,
0.70710678, 0.67155895, 0.63439328, 0.59569930, 0.55557023, 0.51410274, 0.47139674, 0.42755509, 0.92387953, 0.93299280, 0.94154407, 0.94952818, 0.95694034, 0.96377607, 0.97003125, 0.97570213,
0.38268343, 0.33688985, 0.29028468, 0.24298018, 0.19509032, 0.14673047, 0.09801714, 0.04906767, 0.98078528, 0.98527764, 0.98917651, 0.99247953, 0.99518473, 0.99729046, 0.99879546, 0.99969882,
0.00000000, -0.04906767, -0.09801714, -0.14673047, -0.19509032, -0.24298018, -0.29028468, -0.33688985, 1.00000000, 0.99969882, 0.99879546, 0.99729046, 0.99518473, 0.99247953, 0.98917651, 0.98527764,
-0.38268343, -0.42755509, -0.47139674, -0.51410274, -0.55557023, -0.59569930, -0.63439328, -0.67155895, 0.98078528, 0.97570213, 0.97003125, 0.96377607, 0.95694034, 0.94952818, 0.94154407, 0.93299280,
-0.70710678, -0.74095113, -0.77301045, -0.80320753, -0.83146961, -0.85772861, -0.88192126, -0.90398929, 0.92387953, 0.91420976, 0.90398929, 0.89322430, 0.88192126, 0.87008699, 0.85772861, 0.84485357,
-0.92387953, -0.94154407, -0.95694034, -0.97003125, -0.98078528, -0.98917651, -0.99518473, -0.99879546, 0.83146961, 0.81758481, 0.80320753, 0.78834643, 0.77301045, 0.75720885, 0.74095113, 0.72424708,
0.70710678, 0.68954054, 0.67155895, 0.65317284, 0.63439328, 0.61523159, 0.59569930, 0.57580819,
0.55557023, 0.53499762, 0.51410274, 0.49289819, 0.47139674, 0.44961133, 0.42755509, 0.40524131,
0.38268343, 0.35989504, 0.33688985, 0.31368174, 0.29028468, 0.26671276, 0.24298018, 0.21910124,
0.19509032, 0.17096189, 0.14673047, 0.12241068, 0.09801714, 0.07356456, 0.04906767, 0.02454123,
0.00000000, -0.02454123, -0.04906767, -0.07356456, -0.09801714, -0.12241068, -0.14673047, -0.17096189,
-0.19509032, -0.21910124, -0.24298018, -0.26671276, -0.29028468, -0.31368174, -0.33688985, -0.35989504,
-0.38268343, -0.40524131, -0.42755509, -0.44961133, -0.47139674, -0.49289819, -0.51410274, -0.53499762,
-0.55557023, -0.57580819, -0.59569930, -0.61523159, -0.63439328, -0.65317284, -0.67155895, -0.68954054,
-0.70710678, -0.72424708, -0.74095113, -0.75720885, -0.77301045, -0.78834643, -0.80320753, -0.81758481,
-0.83146961, -0.84485357, -0.85772861, -0.87008699, -0.88192126, -0.89322430, -0.90398929, -0.91420976,
-0.92387953, -0.93299280, -0.94154407, -0.94952818, -0.95694034, -0.96377607, -0.97003125, -0.97570213,
-0.98078528, -0.98527764, -0.98917651, -0.99247953, -0.99518473, -0.99729046, -0.99879546, -0.99969882,
}; };
/*** /***
* dir = forward: 0, inverse: 1 * dir = forward: 0, inverse: 1
* https://www.nayuki.io/res/free-small-fft-in-multiple-languages/fft.c * https://www.nayuki.io/res/free-small-fft-in-multiple-languages/fft.c
*/ */
static void fft128(float array[][2], const uint8_t dir) { static void fft256(float array[][2], const uint8_t dir) {
const uint8_t n = 128; const uint16_t n = 256;
const uint8_t levels = 7; // log2(n) const uint8_t levels = 8; // log2(n)
const float* const cos_table = &sin_table[32]; const float* const cos_table = &sin_table[64];
const uint8_t real = dir & 1; const uint8_t real = dir & 1;
const uint8_t imag = ~real & 1; const uint8_t imag = ~real & 1;
for (uint8_t i = 0; i < n; i++) { for (uint16_t i = 0; i < n; i++) {
uint8_t j = reverse_bits(i, levels); uint16_t j = reverse_bits(i, levels);
if (j > i) { if (j > i) {
float temp = array[i][real]; float temp = array[i][real];
array[i][real] = array[j][real]; array[i][real] = array[j][real];
@ -79,12 +91,12 @@ static void fft128(float array[][2], const uint8_t dir) {
} }
// Cooley-Tukey decimation-in-time radix-2 FFT // Cooley-Tukey decimation-in-time radix-2 FFT
for (uint8_t size = 2; size <= n; size *= 2) { for (uint16_t size = 2; size <= n; size *= 2) {
uint8_t halfsize = size / 2; uint16_t halfsize = size / 2;
uint8_t tablestep = n / size; uint16_t tablestep = n / size;
for (uint8_t i = 0; i < n; i += size) { for (uint16_t i = 0; i < n; i += size) {
for (uint8_t j = i, k = 0; j < i + halfsize; j++, k += tablestep) { for (uint16_t j = i, k = 0; j < i + halfsize; j++, k += tablestep) {
uint8_t l = j + halfsize; uint16_t l = j + halfsize;
float tpre = array[l][real] * cos_table[k] + array[l][imag] * sin_table[k]; float tpre = array[l][real] * cos_table[k] + array[l][imag] * sin_table[k];
float tpim = -array[l][real] * sin_table[k] + array[l][imag] * cos_table[k] ; float tpim = -array[l][real] * sin_table[k] + array[l][imag] * cos_table[k] ;
array[l][real] = array[j][real] - tpre; array[l][real] = array[j][real] - tpre;
@ -98,10 +110,10 @@ static void fft128(float array[][2], const uint8_t dir) {
} }
} }
static inline void fft128_forward(float array[][2]) { static inline void fft256_forward(float array[][2]) {
fft128(array, 0); fft256(array, 0);
} }
static inline void fft128_inverse(float array[][2]) { static inline void fft256_inverse(float array[][2]) {
fft128(array, 1); fft256(array, 1);
} }

33
main.c
View file

@ -140,6 +140,7 @@ transform_domain(void)
float* tmp = (float*)spi_buffer; float* tmp = (float*)spi_buffer;
uint8_t window_size, offset; uint8_t window_size, offset;
uint8_t is_lowpass = FALSE;
switch (domain_mode & TD_FUNC) { switch (domain_mode & TD_FUNC) {
case TD_FUNC_BANDPASS: case TD_FUNC_BANDPASS:
offset = 0; offset = 0;
@ -147,6 +148,7 @@ transform_domain(void)
break; break;
case TD_FUNC_LOWPASS_IMPULSE: case TD_FUNC_LOWPASS_IMPULSE:
case TD_FUNC_LOWPASS_STEP: case TD_FUNC_LOWPASS_STEP:
is_lowpass = TRUE;
offset = 101; offset = 101;
window_size = 202; window_size = 202;
break; break;
@ -165,29 +167,38 @@ transform_domain(void)
break; break;
} }
for (int ch = 0; ch < 2; ch++) { for (int ch = 0; ch < 2; ch++) {
memcpy(tmp, measured[ch], sizeof(measured[0])); memcpy(tmp, measured[ch], sizeof(measured[0]));
if (beta != 0.0) { for (int i = 0; i < 101; i++) {
for (int i = 0; i < 101; i++) { float w = kaiser_window(i+offset, window_size, beta);
float w = kaiser_window(i+offset, window_size, beta); tmp[i*2+0] *= w;
tmp[i*2+0] *= w; tmp[i*2+1] *= w;
tmp[i*2+1] *= w;
}
} }
for (int i = 101; i < 128; i++) { for (int i = 101; i < FFT_SIZE; i++) {
tmp[i*2+0] = 0.0; tmp[i*2+0] = 0.0;
tmp[i*2+1] = 0.0; tmp[i*2+1] = 0.0;
} }
fft128_inverse((float(*)[2])tmp); if (is_lowpass) {
for (int i = 1; i < 101; i++) {
tmp[(FFT_SIZE-i)*2+0] = tmp[i*2+0];
tmp[(FFT_SIZE-i)*2+1] = -tmp[i*2+1];
}
}
fft256_inverse((float(*)[2])tmp);
memcpy(measured[ch], tmp, sizeof(measured[0])); memcpy(measured[ch], tmp, sizeof(measured[0]));
for (int i = 0; i < 101; i++) { for (int i = 0; i < 101; i++) {
measured[ch][i][0] /= 128.0; measured[ch][i][0] /= (float)FFT_SIZE;
measured[ch][i][1] /= 128.0; if (is_lowpass) {
measured[ch][i][1] = 0.0;
} else {
measured[ch][i][1] /= (float)FFT_SIZE;
}
} }
if ( (domain_mode & TD_FUNC) == TD_FUNC_LOWPASS_STEP ) { if ( (domain_mode & TD_FUNC) == TD_FUNC_LOWPASS_STEP ) {
for (int i = 1; i < 101; i++) { for (int i = 1; i < 101; i++) {
measured[ch][i][0] += measured[ch][i-1][0]; measured[ch][i][0] += measured[ch][i-1][0];
measured[ch][i][1] += measured[ch][i-1][1];
} }
} }
} }

2
nanovna.h
View file

@ -62,6 +62,8 @@ extern float measured[2][101][2];
#define TD_WINDOW_MINIMUM (0b01<<3) #define TD_WINDOW_MINIMUM (0b01<<3)
#define TD_WINDOW_MAXIMUM (0b10<<3) #define TD_WINDOW_MAXIMUM (0b10<<3)
#define FFT_SIZE 256
void cal_collect(int type); void cal_collect(int type);
void cal_done(void); void cal_done(void);

4
plot.c
View file

@ -702,12 +702,12 @@ trace_get_info(int t, char *buf, int len)
} }
static float time_of_index(int idx) { static float time_of_index(int idx) {
return 1.0 / (float)(frequencies[1] - frequencies[0]) / 128.0 * idx; return 1.0 / (float)(frequencies[1] - frequencies[0]) / (float)FFT_SIZE * idx;
} }
static float distance_of_index(int idx) { static float distance_of_index(int idx) {
#define SPEED_OF_LIGHT 299792458 #define SPEED_OF_LIGHT 299792458
float distance = ((float)idx * (float)SPEED_OF_LIGHT) / ( (float)(frequencies[1] - frequencies[0]) * 128.0 * 2.0); float distance = ((float)idx * (float)SPEED_OF_LIGHT) / ( (float)(frequencies[1] - frequencies[0]) * (float)FFT_SIZE * 2.0);
return distance * (velocity_factor / 100.0); return distance * (velocity_factor / 100.0);
} }