Connect SIN or TRI to the ADC channel zero through the (x+5)/2 amplifier stage to feed a waveform.
Start scilab from the main menu and enter the following commands.
openPhoenix();
selectADC(0);
[t,v] = readBlock(256,150,1);
plot2d(v);
xbasc();
tr = fft(v, -1);
plot2d(abs(tr));

The readblock call will return two vectors (time in 't' and voltage in 'v') having a size of 256. Sampling is done at 150 usec interval and the input is bipolar, from -5V to 5V. Fast Fourier transform is taken and the  modulus is plotted. (tr is an array of complex numbers)

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The interfaing programs that connect Scilab  and C are inside the directory /usr/phoenix/scilab.
(incomplete)