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DSP library for MSP430 and MSP432 version 1_10_00_10搞不懂，请教问题？

user242210
Intellectual 350 points
Other Parts Discussed in Thread: MATHLIB

这几天下了DSP library for MSP430 and MSP432 version 1_10_00_10，试着跑了一下例子，DSPLib_1_10_00_10\examples\Transform，试试FFT功能，里面三个例子，使用IAR编译器。三个例子分别是fft_fixed_q15，cmplx_fft_auto_q15，fft_iq31。Debug使用了simulator。可是看不懂FFT变换后的结果。谁能帮忙解释一下。FFT的结果如何看。

  • 0
    Intellectual 350 points

    例1：fft_fixed_q15：

    看程序是先算出了要变换的数据vectorB=0.25*sin(2*pi*250*t)+0.1*sin(2*pi*1000*t),两路正弦波相加。

    然后使用status = msp_fft_fixed_q15(&fftParams, vectorB);

    不知道这个函数算出来的结果在哪里？256点FFT，vectorB倒是有30个数变化了，可是看不出来和250,1000这两个频率有啥关系。看了函数

    msp_status msp_fft_fixed_q15 ( const msp_fft_q15_params *  params,
    int16_t *  src 
    )

    Real forward FFT function with fixed scaling by two at each stage.

    Details
    Computes the forward discreet Fourier transform (DFT) of 16-bit real inputs. If the inputs are not already in bit reversed order the bit reversal parameter must be set. The output is scaled by a factor of two for each stage of the DFT.
    This functions requires half the data storage and consumes roughly half the cycles and energy as running a complex FFT of the same length. When transforming purely real inputs, such as samples from an ADC or analog sensor, it is recommended to use the real FFT functions.
    When using LEASC the twiddle table pointer can be set to NULL (zero) and the source data must be aligned to LENGTH*2 bytes. For example, a 256 point real FFT must be aligned to a 512 byte address in shared LEA memory.
    Pseudo code
    y = fft(real(x)) ./ (N/2)
    Scaling
    Each stage of the real FFT, with the exception of the final split stage, scales the result by a factor of 0.5. The output format can either be interpreted as the same type with (N/2) scaling or a different fixed point data type. This can be helpful when using the IQmathLib to process the results of the FFT, such as computing the magnitude or phase angle of the complex result.
    LengthInput TypeResult Type
    16 _q15 _q12
    32 _q15 _q11
    64 _q15 _q10
    128 _q15 _q9
    256 _q15 _q8
    512 _q15 _q7
    1024 _q15 _q6
    2048 _q15 _q5
    4096 _q15 _q4
    The following table lists the applied scaling factor and resulting data type when the input is a 16-bit integer.
    LengthInput TypeResult Type
    16 int16_t (int16_t)(result / 8)
    32 int16_t (int16_t)(result / 16)
    64 int16_t (int16_t)(result / 32)
    128 int16_t (int16_t)(result / 64)
    256 int16_t (int16_t)(result / 128)
    512 int16_t (int16_t)(result / 256)
    1024 int16_t (int16_t)(result / 512)
    2048 int16_t (int16_t)(result / 1024)
    4096 int16_t (int16_t)(result / 2048)
    Parameters
    params Pointer to the real FFT parameter structure.
    src Pointer to the real data array to perform the FFT on.
    Returns
    Status of the operation.
    还是一头雾水。谁能帮帮我。
  • 0
    TI__Genius 12740 points

    mathlib还是DSP library?

  • 0 回复 user242210
    Prodigy 10 points

    请问楼主解决了没有，我现在同样遇到这个问题，脑子疼