Question

I can’t see any memory change in my .map file when I try to compare the two different codes.
Is there a “good practice” to follow here? Should I or shouldn’t I put the variables in the header?
As a note, I can have multiple PIDUpdate() functions, I allready have two (if that makes any difference).

First example without variables in the header -> main.c

static int16_t PIDUpdate(int16_t target, int16_t feedback) // Valve
{
static float pTerm, iTerm, dTerm;
static float PID;
int16_t CurrentError;
static float LastError, SumError;
uint16_t tick;
static uint16_t elapsed;
float Kp = 0.1, Ki = 0.1, Kd = 0.1;

Kp = (float) pGain/10000.0;
Ki = (float) iGain/10000.0;
Kd = (float) dGain/10000.0;

....
if(elapsed = tick - timestamp, elapsed < TRACKING_PERIOD)
    goto leave;

timestamp = tick;

CurrentError = target - feedback;

pTerm = Kp * CurrentError;

// Calculate the Integral State with appropriate Limiting
....
iTerm = Ki * SumError;

dTerm = Kd * (LastError - CurrentError);

LastError = CurrentError;

PID = pTerm + iTerm + dTerm;

control = PID;
....
    leave:
return (control);
      }

The other example with variabels in header instead -> main.h

typedef struct PID
{
// PID parameters
uint16_t Kp; // pGain
uint16_t Ki; // iGain
uint16_t Kd; // dGain

// PID calculations
float pTerm;
float iTerm;
float dTerm;
float PID;

// Extra variabels
int16_t CurrentError;

// PID Time
uint16_t tick;

   }pid_object;

   typedef static struct staticPID
   {    
// Extra variabels
int16_t control;
float LastError;
float SumError;

// PID Time
uint16_t elapsed;
uint16_t timestamp;

    }StaticPid_object;

Now the main.c code togheter with above .h-file

static int16_t PIDUpdate(int16_t target, int16_t feedback) // Valve
{
pid_object _PID_t;
StaticPid_object _StatPID_t;

_PID_t.Kp = (float) pGain/10000.0;
_PID_t.Ki = (float) iGain/10000.0;
_PID_t.Kd = (float) dGain/10000.0;

if(_StatPID_t.elapsed = _PID_t.tick - _StatPID_t.timestamp, _StatPID_t.elapsed < TRACKING_PERIOD)
    goto leave;

_StatPID_t.timestamp = _PID_t.tick;

_PID_t.CurrentError = target - feedback;

_PID_t.pTerm = _PID_t.Kp * _PID_t.CurrentError;

// Calculate the Integral State with appropriate Limiting
....

_PID_t.iTerm = _PID_t.Ki * _StatPID_t.SumError;

_PID_t.dTerm = _PID_t.Kd * (_StatPID_t.LastError - _PID_t.CurrentError);

_StatPID_t.LastError = _PID_t.CurrentError;

_PID_t.PID = _PID_t.pTerm + _PID_t.iTerm + _PID_t.dTerm;

_StatPID_t.control = 255-_PID_t.PID; // Make it work oposite to Heater

     leave:
return (_StatPID_t.control);
     }

Answer 1

It doesn’t matter where your code is — in .h or in .c, but if you include the header defining static variable in multiple files, you’ll have different instance for each file. What matters here is if this is what you want.