topic Re: S12XDP512 more efficient between char and int in S12 / MagniV Microcontrollers

S12XDP512 more efficient between char and int

calou — Sat, 17 Mar 2007 00:08:14 GMT

Hello,

I use CW 4.5 for s12x

if i declare a function like it

void f(char i, char j)

{

return(i+j)

}

and the same function like that

void f(int i, int j)

{

return(i+j)

}

What is the best déclaration for the micro (for speed)? I don't really need 16 bit variables but i am translating old functions to a new application for 9s12x and a lot of functions are declared with int for char really needed. If i change all my declarations functions, will my program will work faster?

Regards

Re: S12XDP512 more efficient between char and int

CompilerGuru — Sat, 17 Mar 2007 03:19:54 GMT

I'm not sure, but my feeling is that for the HC12, using unsigned char or unsigned int wont differ a lot in speed.
Some arithmetic operations (or, and,) are faster with unsigned char's but on the other side C rules often require int arithmetic so char's may have to be explicitly zero extended in other cases.
Probably you wont see a huge difference in speed (but in memory usage :smileyhappy:

Daniel

Re: S12XDP512 more efficient between char and int

Alban — Sat, 17 Mar 2007 20:04:51 GMT

Hello,

To know the exact speed, you need to refer to the assembly generated.
The number of instruction will depend on where your values are stored.
S12XCPUVx will give a decomposition of instructions used.

With a char (byte), values can be stored in CPU registers A and B.
But int (word), values will not fit.

As the Guru said, an int will take more memory space.
If it is practical, I advise you to .use the smallest side.
After all, an addition between two "int" can give a "long".

Cheers,
Alban.

Re: S12XDP512 more efficient between char and int

calou — Mon, 19 Mar 2007 17:15:22 GMT

Thank you for help

Regards