Why does the Fixed Point Advisor show a Trigonometric function as unsupported when using CORDIC approximation?

Hello,

The Trigonometric Function in Simulink shows that fixed point data type is supported "only when Approximation method is CORDIC". However, when I use a block in my model with CORDIC approximation and I run the Fixed Point advisor, the third task, "Address Unsupported Blocks" fails, with the failing block being the Trigonometric function, and a suggestion to replace with a lookup table. Thanks.

[Kaustubha Govind]

What version of MATLAB are you using? Are you referring to the documentation installed with your version, or from the web? I suspect that fixed-point support may have been added for the Trignometric block in a fairly recent release.

Answer 1

[Kaustubha Govind]

What version of MATLAB are you using? Are you referring to the documentation installed with your version, or from the web? Fixed-point support for the Trignometric block was added in R2010a. Also, only the 'sin', 'cos', 'sincos' and 'cos+jsin' functions appear to be supported.

Answer 2

[Ali]

I am using the R2012a version. I think the documentation for this issue is the same (installed or web). My question is that I find it strange that the documentation mentions that fixdt is supported for trigonometric functions with CORDIC approximation but the Fixed Point Advisor fails on the third task because the trigonometric function block (configured with CORDIC approximation) is not supported.

[Kaustubha Govind]

Which function have you selected? If it is indeed one of the supported sin, cos, sincos or cos+jsin functions, I would recommend contacting MathWorks Tech Support to see if this is a bug in Fixed-Point Advisor.

[Rafael]

Hello, I am having the same problem on MATLAB R2012b, and it is quite easy to reproduce. Just go to the link on the help for trigonometric functions http://www.mathworks.com/help/simulink/slref/trigonometricfunction.html and open the link under sincos Function with Fixed-Point Input example, it will open the model with this example, then use the Fixed Point Advisor and it will fail marking this block as unsupported. Has a solution been found? Should each of the people that runs into this problem contact MathWorks Tech Support directly?

Answer 3

[Bo]

I also faced this problem when I used fixed point advisor & fixed point tool. Finally, I manually defined all bit widthes so as to avoid the warning. I suggest you use data type conversion model to isolate Trigonometric Function model.