diff --git a/fft.h b/fft.h index 1a46515..0250671 100644 --- a/fft.h +++ b/fft.h @@ -26,8 +26,8 @@ #include #include -static uint8_t reverse_bits(uint8_t x, int n) { - uint8_t result = 0; +static uint16_t reverse_bits(uint16_t x, int n) { + uint16_t result = 0; for (int i = 0; i < n; i++, x >>= 1) result = (result << 1) | (x & 1U); return result; @@ -36,38 +36,50 @@ static uint8_t reverse_bits(uint8_t x, int n) { static const float sin_table[] = { /* * float has about 7.2 digits of precision - for (uint8_t i = 0; i < 96; i++) { - printf("% .8f,%c", sin(2 * M_PI * i / n), i % 8 == 7 ? '\n' : ' '); + for (uint8_t i = 0; i < FFT_SIZE - (FFT_SIZE / 4); i++) { + 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, - 0.38268343, 0.42755509, 0.47139674, 0.51410274, 0.55557023, 0.59569930, 0.63439328, 0.67155895, - 0.70710678, 0.74095113, 0.77301045, 0.80320753, 0.83146961, 0.85772861, 0.88192126, 0.90398929, - 0.92387953, 0.94154407, 0.95694034, 0.97003125, 0.98078528, 0.98917651, 0.99518473, 0.99879546, - 1.00000000, 0.99879546, 0.99518473, 0.98917651, 0.98078528, 0.97003125, 0.95694034, 0.94154407, - 0.92387953, 0.90398929, 0.88192126, 0.85772861, 0.83146961, 0.80320753, 0.77301045, 0.74095113, - 0.70710678, 0.67155895, 0.63439328, 0.59569930, 0.55557023, 0.51410274, 0.47139674, 0.42755509, - 0.38268343, 0.33688985, 0.29028468, 0.24298018, 0.19509032, 0.14673047, 0.09801714, 0.04906767, - 0.00000000, -0.04906767, -0.09801714, -0.14673047, -0.19509032, -0.24298018, -0.29028468, -0.33688985, - -0.38268343, -0.42755509, -0.47139674, -0.51410274, -0.55557023, -0.59569930, -0.63439328, -0.67155895, - -0.70710678, -0.74095113, -0.77301045, -0.80320753, -0.83146961, -0.85772861, -0.88192126, -0.90398929, - -0.92387953, -0.94154407, -0.95694034, -0.97003125, -0.98078528, -0.98917651, -0.99518473, -0.99879546, + 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, + 1.00000000, 0.99969882, 0.99879546, 0.99729046, 0.99518473, 0.99247953, 0.98917651, 0.98527764, + 0.98078528, 0.97570213, 0.97003125, 0.96377607, 0.95694034, 0.94952818, 0.94154407, 0.93299280, + 0.92387953, 0.91420976, 0.90398929, 0.89322430, 0.88192126, 0.87008699, 0.85772861, 0.84485357, + 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 * https://www.nayuki.io/res/free-small-fft-in-multiple-languages/fft.c */ -static void fft128(float array[][2], const uint8_t dir) { - const uint8_t n = 128; - const uint8_t levels = 7; // log2(n) - const float* const cos_table = &sin_table[32]; +static void fft256(float array[][2], const uint8_t dir) { + const uint16_t n = 256; + const uint8_t levels = 8; // log2(n) + const float* const cos_table = &sin_table[64]; const uint8_t real = dir & 1; const uint8_t imag = ~real & 1; - for (uint8_t i = 0; i < n; i++) { - uint8_t j = reverse_bits(i, levels); + for (uint16_t i = 0; i < n; i++) { + uint16_t j = reverse_bits(i, levels); if (j > i) { float temp = array[i][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 - for (uint8_t size = 2; size <= n; size *= 2) { - uint8_t halfsize = size / 2; - uint8_t tablestep = n / size; - for (uint8_t i = 0; i < n; i += size) { - for (uint8_t j = i, k = 0; j < i + halfsize; j++, k += tablestep) { - uint8_t l = j + halfsize; + for (uint16_t size = 2; size <= n; size *= 2) { + uint16_t halfsize = size / 2; + uint16_t tablestep = n / size; + for (uint16_t i = 0; i < n; i += size) { + for (uint16_t j = i, k = 0; j < i + halfsize; j++, k += tablestep) { + uint16_t l = j + halfsize; 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] ; 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]) { - fft128(array, 0); +static inline void fft256_forward(float array[][2]) { + fft256(array, 0); } -static inline void fft128_inverse(float array[][2]) { - fft128(array, 1); +static inline void fft256_inverse(float array[][2]) { + fft256(array, 1); } diff --git a/main.c b/main.c index 3653ca0..9ca5301 100644 --- a/main.c +++ b/main.c @@ -140,6 +140,7 @@ transform_domain(void) float* tmp = (float*)spi_buffer; uint8_t window_size, offset; + uint8_t is_lowpass = FALSE; switch (domain_mode & TD_FUNC) { case TD_FUNC_BANDPASS: offset = 0; @@ -147,6 +148,7 @@ transform_domain(void) break; case TD_FUNC_LOWPASS_IMPULSE: case TD_FUNC_LOWPASS_STEP: + is_lowpass = TRUE; offset = 101; window_size = 202; break; @@ -165,29 +167,38 @@ transform_domain(void) break; } + for (int ch = 0; ch < 2; ch++) { memcpy(tmp, measured[ch], sizeof(measured[0])); - if (beta != 0.0) { - for (int i = 0; i < 101; i++) { - float w = kaiser_window(i+offset, window_size, beta); - tmp[i*2+0] *= w; - tmp[i*2+1] *= w; - } + for (int i = 0; i < 101; i++) { + float w = kaiser_window(i+offset, window_size, beta); + tmp[i*2+0] *= 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+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])); for (int i = 0; i < 101; i++) { - measured[ch][i][0] /= 128.0; - measured[ch][i][1] /= 128.0; + measured[ch][i][0] /= (float)FFT_SIZE; + 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 ) { for (int i = 1; i < 101; i++) { measured[ch][i][0] += measured[ch][i-1][0]; - measured[ch][i][1] += measured[ch][i-1][1]; } } } diff --git a/nanovna.h b/nanovna.h index e60924d..4cddebd 100644 --- a/nanovna.h +++ b/nanovna.h @@ -62,6 +62,8 @@ extern float measured[2][101][2]; #define TD_WINDOW_MINIMUM (0b01<<3) #define TD_WINDOW_MAXIMUM (0b10<<3) +#define FFT_SIZE 256 + void cal_collect(int type); void cal_done(void); diff --git a/plot.c b/plot.c index 83ed0fb..f8fb0c9 100644 --- a/plot.c +++ b/plot.c @@ -702,12 +702,12 @@ trace_get_info(int t, char *buf, int len) } 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) { #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); }