Why do I get an error while trying to compare two numbers of FIXDT data type in my Embedded Matlab Block comparison operator in Simulink 7.3 (R2009a)?

I am comparing two fixed point signals inside of an Embedded MATLAB Block, one of type fixdt(0,9,0), and one of type fixdt(0,7,0), as below:

function y = fcn(u1,u2)

%#eml

if u1>u2

y = 1;

else

      y=0;

end

However, if I change either one to data type fixdt(0,8,0), Simulink changes the data type to a uint8 (not a ufix8), and the Embedded MATLAB block cannot perform the operation. I get the following error:

 In fi > non-fi, the non-fi must be a constant.

 Function 'Embedded MATLAB Function1' (#104.33.38), line 3, column 4:

 "u1>u2"

Answer 1

[MathWorks Support Team]

This is expected behavior. To get the Embedded MATLAB block to recognize this signal as an FI object, please perform the following steps:

There is drop-down menu in the EML Ports and Data Manager that says "Treat these inherited Simulink signal types as fi objects" - select "Fixed-point & integer" for this parameter.

Similarly:

 fixdt(1,8,0) -> int8

 fixdt(0,16,0) -> uint16

 fixdt(1,16,0) -> int16

 fixdt(0,32,0) -> uint32

 fixdt(1,32,0) -> int32

 fixdt(0,64,0) -> uint64 AND

 fixdt(1,64,0) -> int64

If your wordlength is not 8,16,32 or 64 (when fraction length is 0), only then is the type treated as a non-builtin fixed-point type.

Alternately, you can use the following comparison in your EML code:

if u1 > fi(u2,0,8,0)