文件列表:

CE018_FFT_DSPlib\CodeExample.mcp (901, 2007-11-09)
CE018_FFT_DSPlib\CodeExample.mcw (209920, 2005-11-16)
CE018_FFT_DSPlib\dsPICworks\inputsignal_square1khz.fre (4462, 2007-11-09)
CE018_FFT_DSPlib\dsPICworks\inputsignal_square1khz.s (12213, 2007-11-09)
CE018_FFT_DSPlib\dsPICworks\inputsignal_square1khz.tim (737, 2007-11-09)
CE018_FFT_DSPlib\dsPICworks\inputsignal_square1khz_512pt.fre (8564, 2007-11-09)
CE018_FFT_DSPlib\dsPICworks\inputsignal_square1khz_512pt.s (23989, 2007-11-09)
CE018_FFT_DSPlib\dsPICworks\inputsignal_square1khz_512pt.tim (1249, 2007-11-09)
CE018_FFT_DSPlib\gld\linkerscript.gld (457, 2007-11-09)
CE018_FFT_DSPlib\h\fft.h (958, 2007-11-09)
CE018_FFT_DSPlib\inc\dspcommon.inc (5101, 2007-11-09)
CE018_FFT_DSPlib\src\inputsignal_square1khz.c (6197, 2007-11-09)
CE018_FFT_DSPlib\src\main_FFTExample.c (5659, 2007-11-09)
CE018_FFT_DSPlib\src\twiddleFactors.c (12529, 2007-11-09)
CE018_FFT_DSPlib\src\obj (0, 2010-09-03)
CE018_FFT_DSPlib\dsPICworks (0, 2010-09-03)
CE018_FFT_DSPlib\gld (0, 2010-09-03)
CE018_FFT_DSPlib\h (0, 2010-09-03)
CE018_FFT_DSPlib\hex (0, 2010-09-03)
CE018_FFT_DSPlib\inc (0, 2010-09-03)
CE018_FFT_DSPlib\src (0, 2010-09-03)
CE018_FFT_DSPlib (0, 2010-09-03)

Readme File for Code Example: CE018 - Using the Fast Fourier Transform (FFT) for Frequency Detection ---------------------------------------------------------------------- This file contains the following sections: 1. Code Example Description 2. Folder Contents 3. Suggested Development Resources 4. Reconfiguring the project for a different dsPIC30F device 5. Reconfiguring the project for a different FFT Size: 6. Revision History 1. Code Example Description: ---------------------------- Microchip's 16-bit dsPIC Digital Signal Controllers feature a DSP Engine in the CPU that is capable of executing a Fast Fourier Transform (FFT) with great efficiency (high speed and low RAM usage). The on-chip features enabling the FFT implementation include, bit-reversed addressing, Multiply-accumulate (MAC) type instructions and the ability to store and retrieve constants stored in Program memory. Microchip provides a DSP functions library that provides in-place FFT functions. In this code example, we demonstrate how the DSP library functions can be used to perform an FFT on an input signal (vector). The code example is reconfigurable to perfrom an FFT of any size, including common sizes of ***, 128, 256 and 512 points. The code example also allows the user to place the FFT coefficients (known as Twiddle Factors) in RAM or in Program Flash Memory. The project may be easily reconfigured by modifying the header file, FFT.h. By default, the example implements a 256-point FFT using coefficients stored in Program Flash memory. The input signal for our example will be 256 points of a Square wave signal of frequency 1KHz sampled at 10 KHz. This signal was first generated by dsPICworks and then exported as an assembler file from dsPICworks. After exporting it out, the assembler file was modified to ensure the samples reside in Y-data space. The FFT operation is performed on the input signal, in-place. This means that the output of the FFT resides in the same RAM locations where the input signal used to reside. The FFT is performed in the following steps: 1. Initialization: Generate Twiddle Factor Coefficients and store them in X-RAM or alternately use twiddle factor coefficients stored in Program Flash. 2. Scale the input signal to lie within the range [-0.5, +0.5]. For fixed point fractional input data, this translates to input samples in the range [0xC000,0x3FFF]. The scaling is achieved by simply right-shifting the input samples by 1 bit, assuming the input samples lie in the fixed point range [0x8000,0x7FFF] or [-1,+1). 3. Convert the real input signal vector to a complex vector by placing zeros in every other location to signify a complex input whose imaginary part is 0x0000. 4. Butterfly computation: This is achieved by performing a call to the FFTComplexIP() function. 5. Bit-Reversed Re-ordering: The output array is re-ordered to be in bit-reversed order of the addresses. This is achieved by a function call to BitReverseComplex(). 6. SquareMagnitude computation: We then need to compute the magnitude of each complex element in the output vector, so that we can estimate the energy in each spectral component/frequency bin. This is achieved by a call to a special C-callable routine, SquareMagnitudeCplx(), written in assembler language. This routine will be incorporated into the DSP library in future revisions of the C30 toolsuite. At that time, you may remove the source file, cplxsqrmag.s from the project and include the latest DSP library file, libdsp-coff.a. 7. Peak-picking: We then find the frequency component with the largest energy by using the VectorMax() routine in the DSP library. 8. Frequency Calculation: The value of the spectral component with the highest energy, in Hz, is calculated by multiplying the array index of the largest element in the output array with the spectral (bin) resolution ( = sampling rate/FFT size). 2. Folder Contents: ------------------- This folder contains the following sub-folders: a. gld This folder contains the linker script file for the example project. This file is used for building the project. This file was provided with the MPLAB C30 v1.33 toolsuite. b. h This folder contains C header files useful in building this project. Device register and bit definitions are provided in the *.h file that follows the device name. These files were provided with the MPLAB C30 v1.33 toolsuite. c. hex This folder contains three file types - coff, hex and map. These are files generated by the MPLAB C30 toolsuite on build operation performed within MPLAB IDE. The *.map file contains details on memory allocation for various variables, constants and dsPIC30F instructions specified in the source and library code. The *.hex file contains a binary file that may be programmed into the dsPIC30F device. The *.coff file contains a binary file that is used by MPLAB IDE for simulation. d. inc This folder contains Assembler include files useful in building this project. Device register and bit definitions are provided in the *.inc file that follows the device name. These files were provided with the MPLAB C30 v1.33 toolsuite. e. lib This folder contains library archive files, which are a collection of precompiled object files. The file named "libpic30-coff.a" contains the C run-time start-up library. These file were provided with the MPLAB C30 v1.33 toolsuite. f. src This folder contains all the C and Assembler source files (*.c, *.s) used in demonstrating the described example. This folder also contains a sub-folder named "obj" that stores compiled object files generated when the project is built. g. dsPICworks This folder contains files created by dsPIC Filter Design and dsPICworks Data Analysis and Design Software. Input signal files, output signal files and filter specifications have been provided here. 3. Suggested Development Resources: ----------------------------------- a. MPLAB IDE v7.21 or later b. MPLAB C30 v1.33 or later c. MPLAB ICD 2 R23 or later d. dsPICDEM 1.1 Development Board (See below) e. dsPIC30F6014A Digital Signal Controller Plug-In Module (See below) 4. Reconfiguring the project for a different dsPIC30F device: ------------------------------------------------------------- The Project/Workspace can be easily reconfigured for any dsPIC30F device. Please use the following general guidelines: a. Change device selection within MPLAB IDE to a dsPIC30F device of your choice by using the following menu option: MPLAB IDE>>Configure>>Select Device b. Provide the correct device linker script and header file for your device. Device linker scripts and header files are available in your MPLAB C30 installation folder under: Device Linker Script- YourDrive:>Program Files\Microchip\MPLAB C30\support\gld Device C Header file- YourDrive:>Program Files\Microchip\MPLAB C30\support\h Device ASM Include file- YourDrive:>Program Files\Microchip\MPLAB C30\support\inc c. Provide the appropriate path to your MPLAB C30 support file locations using the menu option: MPLAB IDE>>Project>>Build Options>>Project d. Chose the development board applicable to your device. Some options are provided below: - dsPICDEM 2 Development Board supports: 30F2010, 30F2011, 30F2012, 30F3010, 30F3011, 30F3012, 30F3013, 30F3014, 30F4011, 30F4012, 30F4013 - dsPICDEM 1.1 Development Board supports: 30F5013, 30F6010, 30F6011, 30F6012, 30F6013, 30F6014, 30F6011A, 30F6012A, 30F6013A, 30F6014A - dsPICDEM MC1 Development Board supports: 30F6010, 30F6010A, 30F5016 e. Re-build the MPLAB project using the menu option: MPLAB IDE>>Project>>Build All f. Download the hex file into the device and run. 5. Reconfiguring the project for a different FFT Size: ------------------------------------------------------------- The project has been configured for a 256-pt FFT to be performed on a 30F6014A device. Perform the following steps in sequence to change the device and FFT size. (i) Change device selection within MPLAB IDE to a dsPIC30F device of your choice by using the following menu option: MPLAB IDE>>Configure>>Select Device (ii) Provide the correct device linker script and header file for your device. Device linker scripts and header files are available in your MPLAB C30 installation folder under: Device Linker Script- YourDrive:>Program Files\Microchip\MPLAB C30\support\gld Device C Header file- YourDrive:>Program Files\Microchip\MPLAB C30\support\h Device ASM Include file- YourDrive:>Program Files\Microchip\MPLAB C30\support\inc (iii) In the file FFT.h, perform the following changes: - Change FFT_BLOCK_LENGTH to either ***, 128, 256 or 512 - Correspondingly, change LOG2_BLOCK_LENGTH to either 6, 7, 8 or 9 respectively - If you would like to store Twiddle Factors coefficients in RAM instead of Program Memory comment out the line of code as shown: "//#define FFTTWIDCOEFFS_IN_PROGMEM " (iv) This project uses an input squarewave signal provided as PCM samples in the file, "inputsignal_square1khz.c" in the array named "sigCmpx[]". This array should be of length, FFT_BLOCK_LENGTH and type "fractcomplex". So, for a ***-pt FFT, it should contain only *** data samples and padded initially with *** zeroes. This array stores the output of the complex FFT operation and eventually stores the magnitudes of the frequency bins. Modify this array to suit the FFT size you are using. In a real application, your data will likely be input from a real-world signal. (v) Re-build the MPLAB project using the menu option: MPLAB IDE>>Project>>Build All (vi) Download the hex file into the device and run. 6. Revision History : --------------------- 09/30/2005 - Initial Release of the Code Example 01/05/2006 - Corrected cplxsqrmag.s 01/17/2006 - Added "5. Reconfiguring the project for a different FFT Size:" in this readme file and corrected an extern definition in the main_FFTExample.c file

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