readme.txt

TI提供的基于TMS320C24x系列DSP的快速傅立叶变换函数库

;*************************************************************************************
;*********************** SECTION 1: FFT LIBRARY *********************************** 
;*************************************************************************************
Thank you for trying C2000 Software Collateral. 
FFT Library is installed in C:\TIDCS\C24\DSP_TBOX\FFT directory.

Fast Fourier Transforms are an efficient class of algorithms for the digital computation 
of the N-point Fourier transform (DFT). In general, their input sequence are assumed to 
be complex.  In many real applications, the data sequences to be processed are real valued. 
Even though the data is real, complex-valued DFT algorithm can still be used. One simple 
approach creates a complex sequence from the real sequence; that is, real data for the real 
components and zeros for the imaginary components, The complex FFT can then be =applied directly. 


However, this method is not efficient as it consumes 2N memory locations (Real & Imaginary) 
for N point sequence. When input is purely real, their symmetric properties compute DFT very 
efficiently. One such optimized real FFT algorithm for 2N-point real data sequence is packing 
algorithm. The original 2N-point sequence is packed as N-point complex sequence and N -point 
complex FFT is performed on the complex sequence. Finally the resulting N -point complex output 
is unpacked into another N+1 point complex sequence, which corresponds to spectral bin 0 to N 
of 2N-point real input sequence. Spectral bin 0 to N is sufficient, as the remaining bins N+1 
to 2N-1 are complex conjugates of spectral bins N-1 to 1. 

The real FFT requires 2N+2 memory locations to compute the FFT for 2N-point real valued sequence, 
which is highly preferable in contrast to the complex FFT that consumes 4N-locations for 2N-point 
real valued sequence. Moreover using this strategy, the complex FFT size can be reduced by half, 
at the FFT cost function of O(N) operations to pack the input and unpack the output. Hence, 
the real FFT algorithm computes the FFT of a real input sequence almost twice as fast as the 
general FFT algorithm.

This FFT library contains 128, 256 & 512 point real/complex FFT and they are summarized in the below table.


FFT LIBRARY
|===============|======================================================================|
|  Module Name	| Description						               |
|===============|======================================================================| 
| FFT128C 	| 128-point complex FFT module		  			       |
|---------------|----------------------------------------------------------------------|
| FFT256C 	| 256-point complex FFT module					       |
|---------------|----------------------------------------------------------------------|
| FFT512C 	| 512-point complex FFT module					       |
|---------------|----------------------------------------------------------------------|
| FFT128R 	| 128-point real FFT module 					       |
|---------------|----------------------------------------------------------------------|
| FFT256R 	| 256-point real FFT module					       |
|---------------|----------------------------------------------------------------------|
| FFT512R 	| 512-point real FFT module					       |
|======================================================================================|
 

DOCUMENTATION:
|===============|======================================================================|
|  DOC		| DIRECTORY LOCATION				        	       |
|===============|======================================================================| 
|  MODULE DOC	| C:\TIDCS\C24\DSP_TBOX\FFT\DOC\FFT_MDL.PDF	  	               |
|---------------|----------------------------------------------------------------------|
|  STB DOC	| C:\TIDCS\C24\DSP_TBOX\FFT\DOC\FFT_STB.PDF		               |
|======================================================================================|


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;******************** SECTION 2: Software Test Bench (STB) *************************** 
;*************************************************************************************
To facilitate evaluation and deployment of these modules, they are made available as 
Software Test Benches (STBs) which run as code composer projects on readily available 
EVMs or eZdsp hardware platforms. 

Each STB focuses on a particular software module and shows the customer how to invoke it, 
pass variable or data to it, and how to link it into their systems. Where possible, the 
module under evaluation is made to interact with other modules such as signal generators, 
which can provide input stimulus and data-logging modules or PWM-DAC drivers to examine a 
module's response in a real-time environment. This helps customers to get a more realistic 
feel of the software module's capability and applicability. 

Shown below is the STB for FFT module.
                                            IPCB                 MAG
  CH0  |--------------|                     |--|   |--------|   |--|                     |------|
  ---->|              |           	    |--|-->|        |   |--|  |----------------->|Graph1|     
  CH0  |              |         |--------|  |--|<--|FFTcalc |   |--|  |                  |------|
  ---->|     	      |xn=CH0   |	 |  |--|   |        |   |--|  |       
  CH0  |   ADC04U_DRV |----|--->|FFTCACQ |->|--|   |--------|   |--|--|  |-----------|
  ---->|              |    |    |  	 |  |--|   |        |   |--|     |           |   |------|
  CH0  |              |    |    |--------|  |--|-->|FFTmag  |-->|--|  |->|  DATALOG  |-->|Graph2|
  --|->|              |    |      	    |--|   |        |   |--|  |  |           |   |------|
       |--------------|    |      	    |--|   |--------|   |--|  |  |-----------|
                           |                                          |
                           |------------------------------------------|
 

The idea behind the STB strategy to demonstrate the FFT module is indeed simple. A
block of N data sample is sampled/acquired using ADC (20Khz Sampling frequency) and
then processed by the N-pint Real or Complex FFT module to determine the spectral
content. Magnitude-square of all the spectral bins are updated along with input signal on
the CCS graph window using Real Time Monitor for observation. User can quickly start
evaluating the FFT modules by sweeping the input frequency and observing the spectral
response.