基于MSP430、FFT的频率计

#include <msp430f2491.h> #include "includes.h" // Written by Tom Roberts (1989), improved by Malcolm Slaney (1994), made portable (ix86 assembly removed) by Dimitrios P. Bouras (2006). /* fix_fft.c - Fixed-point in-place Fast Fourier Transform */ /* All data are fixed-point short integers, in which -32768 to +32768 represent -1.0 to +1.0 respectively. Integer arithmetic is used for speed, instead of the more natural floating-point. For the forward FFT (time -> freq), fixed scaling is performed to prevent arithmetic overflow, and to map a 0dB sine/cosine wave (i.e. amplitude = 32767) to two -6dB freq coefficients. The return value is always 0. For the inverse FFT (freq -> time), fixed scaling cannot be done, as two 0dB coefficients would sum to a peak amplitude of 64K, overflowing the 32k range of the fixed-point integers. Thus, the fix_fft() routine performs variable scaling, and returns a value which is the number of bits LEFT by which the output must be shifted to get the actual amplitude (i.e. if fix_fft() returns 3, each value of fr[] and fi[] must be multiplied by 8 (2**3) for proper scaling. Clearly, this cannot be done within fixed-point short integers. In practice, if the result is to be used as a filter, the scale_shift can usually be ignored, as the result will be approximately correctly normalized as is. Written by: Tom Roberts 11/8/89 Made portable: Malcolm Slaney 12/15/94 malcolm@interval.com Enhanced: Dimitrios P. Bouras 14 Jun 2006 dbouras@ieee.org */ #define N_WAVE 1024 /* full length of Sinewave[] */ #define LOG2_N_WAVE 10 /* log2(N_WAVE) */ /* Henceforth "short" implies 16-bit word. If this is not the case in your architecture, please replace "short" with a type definition which *is* a 16-bit word. */ /* Since we only use 3/4 of N_WAVE, we define only this many samples, in order to conserve data space. */ const short Sinewave[N_WAVE-N_WAVE/4] = { 0, 201, 402, 603, 804, 1005, 1206, 1406, 1607, 1808, 2009, 2209, 2410, 2610, 2811, 3011, 3211, 3411, 3611, 3811, 4011, 4210, 4409, 4608, 4807, 5006, 5205, 5403, 5601, 5799, 5997, 6195, 6392, 6589, 6786, 6982, 7179, 7375, 7571, 7766, 7961, 8156, 8351, 8545, 8739, 8932, 9126, 9319, 9511, 9703, 9895, 10087, 10278, 10469, 10659, 10849, 11038, 11227, 11416, 11604, 11792, 11980, 12166, 12353, 12539, 12724, 12909, 13094, 13278, 13462, 13645, 13827, 14009, 14191, 14372, 14552, 14732, 14911, 15090, 15268, 15446, 15623, 15799, 15975, 16150, 16325, 16499, 16672, 16845, 17017, 17189, 17360, 17530, 17699, 17868, 18036, 18204, 18371, 18537, 18702, 18867, 19031, 19194, 19357, 19519, 19680, 19840, 20000, 20159, 20317, 20474, 20631, 20787, 20942, 21096, 21249, 21402, 21554, 21705, 21855, 22004, 22153, 22301, 22448, 22594, 22739, 22883, 23027, 23169, 23311, 23452, 23592, 23731, 23869, 24006, 24143, 24278, 24413, 24546, 24679, 24811, 24942, 25072, 25201, 25329, 25456, 25582, 25707, 25831, 25954, 26077, 26198, 26318, 26437, 26556, 26673, 26789, 26905, 27019, 27132, 27244, 27355, 27466, 27575, 27683, 27790, 27896, 28001, 28105, 28208, 28309, 28410, 28510, 28608, 28706, 28802, 28897, 28992, 29085, 29177, 29268, 29358, 29446, 29534, 29621, 29706, 29790, 29873, 29955, 30036, 30116, 30195, 30272, 30349, 30424, 30498, 30571, 30643, 30713, 30783, 30851, 30918, 30984, 31049, 31113, 31175, 31236, 31297, 31356, 31413, 31470, 31525, 31580, 31633, 31684, 31735, 31785, 31833, 31880, 31926, 31970, 32014, 32056, 32097, 32137, 32176, 32213, 32249, 32284, 32318, 32350, 32382, 32412, 32441, 32468, 32495, 32520, 32544, 32567, 32588, 32609, 32628, 32646, 32662, 32678, 32692, 32705, 32717, 32727, 32736, 32744, 32751, 32757, 32761, 32764, 32766, 32767, 32766, 32764, 32761, 32757, 32751, 32744, 32736, 32727, 32717, 32705, 32692, 32678, 32662, 32646, 32628, 32609, 32588, 32567, 32544, 32520, 32495, 32468, 32441, 32412, 32382, 32350, 32318, 32284, 32249, 32213, 32176, 32137, 32097, 32056, 32014, 31970, 31926, 31880, 31833, 31785, 31735, 31684, 31633, 31580, 31525, 31470, 31413, 31356, 31297, 31236, 31175, 31113, 31049, 30984, 30918, 30851, 30783, 30713, 30643, 30571, 30498, 30424, 30349, 30272, 30195, 30116, 30036, 29955, 29873, 29790, 29706, 29621, 29534, 29446, 29358, 29268, 29177, 29085, 28992, 28897, 28802, 28706, 28608, 28510, 28410, 28309, 28208, 28105, 28001, 27896, 27790, 27683, 27575, 27466, 27355, 27244, 27132, 27019, 26905, 26789, 26673, 26556, 26437, 26318, 26198, 26077, 25954, 25831, 25707, 25582, 25456, 25329, 25201, 25072, 24942, 24811, 24679, 24546, 24413, 24278, 24143, 24006, 23869, 23731, 23592, 23452, 23311, 23169, 23027, 22883, 22739, 22594, 22448, 22301, 22153, 22004, 21855, 21705, 21554, 21402, 21249, 21096, 20942, 20787, 20631, 20474, 20317, 20159, 20000, 19840, 19680, 19519, 19357, 19194, 19031, 18867, 18702, 18537, 18371, 18204, 18036, 17868, 17699, 17530, 17360, 17189, 17017, 16845, 16672, 16499, 16325, 16150, 15975, 15799, 15623, 15446, 15268, 15090, 14911, 14732, 14552, 14372, 14191, 14009, 13827, 13645, 13462, 13278, 13094, 12909, 12724, 12539, 12353, 12166, 11980, 11792, 11604, 11416, 11227, 11038, 10849, 10659, 10469, 10278, 10087, 9895, 9703, 9511, 9319, 9126, 8932, 8739, 8545, 8351, 8156, 7961, 7766, 7571, 7375, 7179, 6982, 6786, 6589, 6392, 6195, 5997, 5799, 5601, 5403, 5205, 5006, 4807, 4608, 4409, 4210, 4011, 3811, 3611, 3411, 3211, 3011, 2811, 2610, 2410, 2209, 2009, 1808, 1607, 1406, 1206, 1005, 804, 603, 402, 201, 0, -201, -402, -603, -804, -1005, -1206, -1406, -1607, -1808, -2009, -2209, -2410, -2610, -2811, -3011, -3211, -3411, -3611, -3811, -4011, -4210, -4409, -4608, -4807, -5006, -5205, -5403, -5601, -5799, -5997, -6195, -6392, -6589, -6786, -6982, -7179, -7375, -7571, -7766, -7961, -8156, -8351, -8545, -8739, -8932, -9126, -9319, -9511, -9703, -9895, -10087, -10278, -10469, -10659, -10849, -11038, -11227, -11416, -11604, -11792, -11980, -12166, -12353, -12539, -12724, -12909, -13094, -13278, -13462, -13645, -13827, -14009, -14191, -14372, -14552, -14732, -14911, -15090, -15268, -15446, -15623, -15799, -15975, -16150, -16325, -16499, -16672, -16845, -17017, -17189, -17360, -17530, -17699, -17868, -18036, -18204, -18371, -18537, -18702, -18867, -19031, -19194, -19357, -19519, -19680, -19840, -20000, -20159, -20317, -20474, -20631, -20787, -20942, -21096, -21249, -21402, -21554, -21705, -21855, -22004, -22153, -22301, -22448, -22594, -22739, -22883, -23027, -23169, -23311, -23452, -23592, -23731, -23869, -24006, -24143, -24278, -24413, -24546, -24679, -24811, -24942, -25072, -25201, -25329, -25456, -25582, -25707, -25831, -25954, -26077, -26198, -26318, -26437, -26556, -26673, -26789, -26905, -27019, -27132, -27244, -27355, -27466, -27575, -27683, -27790, -27896, -28001, -28105, -28208, -28309, -28410, -28510, -28608, -28706, -28802, -28897, -28992, -29085, -29177, -29268, -29358, -29446, -29534, -29621, -29706, -29790, -29873, -29955, -30036, -30116, -30195, -30272, -30349, -30424, -30498, -30571, -30643, -30713, -30783, -30851, -30918, -30984, -31049, -31113, -31175, -31236, -31297, -31356, -31413, -31470, -31525,