AN3348

Functional incompatibilities

Doc ID 018510 Rev 2

7/10

MC_CTRL_PID:

/* Inputs:

*/

/* register a ...... error */

/* register diob ... p_pid */

/* Limit error to range <MIN24, MAX24>

*/

if V == 0 then goto MC_CTRL_PID_I, flush.

if N == 0 then goto MC_CTRL_PID_I, no_flush.

…

#endasm

}

2.

The function's prototype is a very important feature that was quite disregarded by the

old tools. The prototype contains information regarding the function which is used by

the caller function in order to create a correct and safe code which would not destroy

local variables which are used in the caller function. That is why it is very important to

create a full prototype for the function. In this function we can see that the function

expects the arguments to be passed through registers a and diob. This information

should be in the prototype. Now the comments which describe that are also redundant

and we can remove them:

fract24 MC_CTRL_PID( register_a fract24 error,

register_diob mc_ctrl_pid_t *p_pid)

{

#asm

/* Limit error to range <MIN24, MAX24>

*/

if V == 0 then goto MC_CTRL_PID_I, flush.

if N == 0 then goto MC_CTRL_PID_I, no_flush.

…

#endasm

}

3.

Since this is a pure assembly function and we don't want the compiler to generate any

prologue and epilogue to it and do not perform any optimizations inside it, we should

add it as an attribute to the function. If the function does not contain an rtn instruction

at it's end and you want the compiler to generate it you can use attribute

no_save_registers

instead of pure_assembly.

4.

Since the function is having also a hidden argument which is the flags (V and N at the

first two lines of the function) we should add also this information into the function's

prototype so that the optimizer would know that flags are important to this function so

flags generation in the caller function should not be optimized away:

__attribute__((expects_flags)) __attribute__((pure_assembly))

fract24 MC_CTRL_PID( register_a fract24 error, register_diob

mc_ctrl_pid_t *p_pid)

{

#asm

/* Limit error to range <MIN24, MAX24>

*/

if V == 0 then goto MC_CTRL_PID_I, flush.

if N == 0 then goto MC_CTRL_PID_I, no_flush.

…

#endasm

}