Matlab question. How to export fixed point array to C header?

Hi Jonathan,

Can you please provide some specifics.  Are you refering to the FFT code that we have released in Open Source on code.google, or some other FFT code?  Also what app note are you refering to?

Best regards, Vishal

Vishal,

Let me clarify. I am referring to the FFT filter code that was recently released on code.google for the C5505 USB Stick. When I mentioned "app note", what I really meant was the release notes that were included with the FFT filter package. Basically, I want to be able to export a sine wave from Matlab in the S16Q15 format. 

I'm sure the steps are quite simple, and I'm hoping that someone here can give me a quick pointer. I have access to Matlab's fixed-point toolbox.

Thanks,

Jonathan

Vishal,

I believe I answered my own question with a bit more digging. I was able to generate a fixed-point representation in Matlab and export it using fprintf. My issue was that I wasn't aware that I could just use the hex function on the fi object. So for posterity, I'll post this snippet of Matlab code.

fs=48000;

t=0:1/fs:0.001;

x = sin(2*pi*5000*t); % for 5Khz sine

xfi = fi(x,1,16,15); % S16Q15  signed, 16 bit word, fraction length 15

fd = fopen('sin5k.txt', 'w');

for i=1:length(x)

  fprintf( fd,'0x%s, ',hex(xfi(k)) );

end

fclose(fd);

Hopefully others new to the fixed-point toolbox will find this useful.

Jonathan

Here's another way to use MATLAB to write a fixed-point sine wave to file.
You can copy and paste the contents of this file into Code Composer directly.

fs = 48000;                         % sampling frequency
N = 48*2;                           % signal length
sig = zeros(1,N);                   % create sig buffer
n = 0:(N-1);                       

%Create 1kHz tone
fk = 1000;                          % signal frequency
A = 0.8;                            % peak amplitude
sig = A * sin(2*pi*n*fk/fs);        % create sampled sine signal

%Quantize sig to S16Q15 fixed point
sig_fixed = fi(sig,1,16,15);             % fi(source, signed, word length,  fraction length (best precision)
sig_fixed_hex = sig_fixed.hex;      % extract hex of sig_fixed

%plot sig_fixed
plot(sig_fixed);

%Split sig_fixed_hex from one string to array of strings
sig_fixed_hex_split = regexp(sig_fixed_hex,'\s*','split');

%Print sig_fixed_hex to a file
file = fopen('fixed-sine.dat','w');
cols = 8;
for i = 0:cols:N-1
    for j = 1:cols
        fprintf(file,'0x%s, ',char(sig_fixed_hex_split(i+j)));
    end
    fprintf(file,'\n');
end

fclose(file);                             %You must manually delete the comma after the last entry in the file!!

Hope this helps,
Mark

Thanks Mark,

This example is cleaner than mine.

Jonathan