[SOLVED] cordic calculations of sine and cosine functions in fpga

[brainiac_rus]

Hi all!

I tryed to calculate a value of sine and cosine functions using cordic algorithm. But it does not work in fixed point system and i wrote it as simple program.

Here is a code:

module cordic_test0(
    );
real cordic_iter[15:0];

real angle;
integer i = 0;
real xi;
real yi;
real zi;


initial begin
	cordic_iter[0] = 45.0;
	cordic_iter[1] = 26.56505118;
	cordic_iter[2] = 14.03624347;
	cordic_iter[3] = 7.125016349;
	cordic_iter[4] = 3.576334375;
	cordic_iter[5] = 1.789910608;
	cordic_iter[6] = 0.89517371;
	cordic_iter[7] = 0.447614171;
	cordic_iter[8] = 0.2238105;
	cordic_iter[9] = 0.111905677;
	cordic_iter[10] = 0.055952892;
	cordic_iter[11] = 0.027976453;
	cordic_iter[12] = 0.013988227;
	cordic_iter[13] = 0.006994114;
	cordic_iter[14] = 0.003497057;
	cordic_iter[15] = 0.001748528;
	#100;
	angle = 45.0;
	zi = angle;
	xi = 0.6071;
	yi = 0.0;
	for(i = 0; i < 16; i = i + 1)
		begin
			if(zi > 0)
				begin
					zi = zi - cordic_iter[i];
					xi = xi - (yi / 2.0**i);//cos
					yi = yi + (xi / 2.0**i);//sin
				end
			else
				begin
					zi = zi + cordic_iter[i];
					xi = xi + (yi / 2.0**i);
					yi = yi - (xi / 2.0**i);
				end
			$display(i,"  ", zi);
			$display(xi,"   ", yi);
		end
	$display("Cos angle is ", xi);
	$display("Sin angle is ", yi);
	$display("Cos angle is ", xi*0.6071);
	$display("Sin angle is ", yi*0.6071);
	#100;
	$stop;
end



endmodule

But it does not work again.
I use this article as source http://andraka.com/files/crdcsrvy.pdf
What is wrong in my code? I think there are some stupied errors, but i can't find it.

this is what i see in console

          0  0
0.6071   0.6071
          1  26.5651
0.91065   0.151775
          2  12.5288
0.872706   0.369952
          3  5.40379
0.826462   0.473259
          4  1.82746
0.796884   0.523065
          5  0.0375464
0.780538   0.547456
          6  -0.857627
0.771984   0.559519
          7  -0.410013
0.776355   0.553453
          8  -0.186203
0.778517   0.550412
          9  -0.074297
0.779592   0.54889
         10  -0.0183441
0.780128   0.548128
         11  0.00963236
0.780396   0.547747
         12  -0.00435587
0.780262   0.547937
         13  0.00263825
0.780329   0.547842
         14  -0.000858809
0.780295   0.54789
         15  0.000889719
0.780312   0.547866
Cos angle is 0.780312
Sin angle is 0.547866
Cos angle is 0.473727
Sin angle is 0.332609

 

[std_match]

"i" should probably start at 1 in the loop, not 0.

 

[brainiac_rus]

No, this is wrong, because input angles are from -pi/2 to pi/2 and first angle which tg(phi) = 2^0, i.e. 45 degrees

 

[std_match]

Ok, I see the problem:

zi = zi - cordic_iter[i];
xi = xi - (yi / 2.0**i);//cos
yi = yi + (xi / 2.0**i);//sin

In the third line you are using the new value for xi, it should be the old value.

 

[brainiac_rus]

Ahahahahaah!!!!!
This is professional deformation!!! I started to think parallel as an FPGA)))

Thank you so much!