Bit Reverse (Embedded Target for Texas Instruments C6000 DSPs)

Embedded Target for Texas Instruments C6000 DSPs

Bit-reverse the positions of the elements of each channel of a complex input signal

Library

C62x DSP Library--Transforms

Description

The Bit Reverse block bit-reverses the elements of each channel of a complex input signal, X. The Bit Reverse block is primarily used to provide correctly-ordered inputs and outputs to or from blocks that perform FFTs. Inputs to this block must be 16-bit fixed-point data types.

The Bit Reverse block supports discrete sample times and little-endian code generation only.

Dialog Box

Algorithm

In simulation, the Bit Reverse block is equivalent to the TMS320C62x DSP Library assembly code function DSP_bitrev_cplx. During code generation, this block calls the DSP_bitrev_cplx routine to produce optimized code.

Examples

The Bit Reverse block reorders the output of the Radix-2 FFT in the model below to natural order.

The following code calculates the same FFT in the workspace. The output from this calculation, y2, is displayed side-by-side with the output from the model, c. The outputs match, showing that the Bit Reverse block reorders the Radix-2 FFT output to natural order:

k = 4;
n = 2^k;
xr = zeros(n, 1);
xr(2) = 0.5;
xi = zeros(n, 1);
x2 = complex(xr, xi);
y2 = fft(x2);

[y2, c]
   0.5000             0.5000          
   0.4619 - 0.1913i   0.4619 - 0.1913i
   0.3536 - 0.3536i   0.3535 - 0.3535i
   0.1913 - 0.4619i   0.1913 - 0.4619i
        0 - 0.5000i        0 - 0.5000i
  -0.1913 - 0.4619i  -0.1913 - 0.4619i
  -0.3536 - 0.3536i  -0.3535 - 0.3535i
  -0.4619 - 0.1913i  -0.4619 - 0.1913i
  -0.5000            -0.5000          
  -0.4619 + 0.1913i  -0.4619 + 0.1913i
  -0.3536 + 0.3536i  -0.3535 + 0.3535i
  -0.1913 + 0.4619i  -0.1913 + 0.4619i
        0 + 0.5000i        0 + 0.5000i
   0.1913 + 0.4619i   0.1913 + 0.4619i
   0.3536 + 0.3536i   0.3535 + 0.3535i
   0.4619 + 0.1913i   0.4619 + 0.1913i

See Also

Radix-2 FFT, Radix-2 IFFT

Autocorrelation Block Exponent