C code interrupt setup from manufacturer - c

Question

The code snippets below come from the manufacturer. I am completely confused as to what they are trying to do. In particular, anything to do with InterruptHandler.
Please comment on the code in the globals section. Does this look right?
Also the various APIs included all have sticking points for me. Are they trying to use a void pointer? ... Plenty to ask, please comment mainly on how they are suggesting the timer2 would work.
...
/**
Section: Global Variables Definitions
*/
void (*TMR2_InterruptHandler)(void);
...
/**
Section: TMR2 APIs
*/
void TMR2_Initialize(void)
{
// Set TMR2 to the options selected in the User Interface
// T2CKPS 1:2; T2OUTPS 1:2; TMR2ON off;
T2CON = 0x11;
// T2CS LFINTOSC;
T2CLKCON = 0x04;
// T2PSYNC Not Synchronized; T2MODE Software control One shot; T2CKPOL Rising Edge; T2CKSYNC Not Synchronized;
T2HLT = 0x08;
// T2RSEL TMR4_postscaled;
T2RST = 0x02;
// PR2 8;
T2PR = 0x08;
// TMR2 0;
T2TMR = 0x00;
// Clearing IF flag before enabling the interrupt.
PIR4bits.TMR2IF = 0;
// Enabling TMR2 interrupt.
PIE4bits.TMR2IE = 1;
// Set Default Interrupt Handler
TMR2_SetInterruptHandler(TMR2_DefaultInterruptHandler);
// Start TMR2
TMR2_Start();
}
void TMR2_ISR(void)
{
// clear the TMR2 interrupt flag
PIR4bits.TMR2IF = 0;
if(TMR2_InterruptHandler)
{
TMR2_InterruptHandler();
}
}
void TMR2_SetInterruptHandler(void* InterruptHandler)
{
TMR2_InterruptHandler = InterruptHandler;
}
void TMR2_DefaultInterruptHandler(void)
{
// add your TMR2 interrupt custom code
// or set custom function using TMR2_SetInterruptHandler()
}
/**
End of File
*/
Thanks,
Steve
edit:
The manufacturer code includes a routine (I can't seem to add it here) for managing high-level interrupts that calls TMR2_ISR if (PIE4bits.TMR2IE == 1 && PIR4bits.TMR2IF == 1) This would seem to negate any TMR2_DefaultInterruptHandler would it not?
Thanks again for your help.

Answer 1

The comments of Garr Godfrey and Martin James provided helpful hints. Thus, I will try to fill the possible gaps:
void (*TMR2_InterruptHandler)(void); is a global variable with a function pointer providing the current interrupt handler.
I would read TMR2_ISR() as "interrupt service routine". From the presented code, it's not clear from where it is called. Suspecting from it's name, it's reasonable to assume that it's called when the interrupt is triggered. It checks whether the global interrupt handler function pointer TMR2_InterruptHandler is not NULL and calls the pointed function in case of success.
If TMR2_Initialize() has been called before then TMR2_InterruptHandler points to function TMR2_DefaultInterruptHandler(). Thus, in this case, the latter is called from TMR2_ISR().
void TMR2_SetInterruptHandler(void* InterruptHandler) is used in TMR2_Initialize(). It sets the current interrupt handler. (Surprise.)
I'm a little bit puzzled because I would make it:
void TMR2_SetInterruptHandler(void (*InterruptHandler)())
This is because my daily work with C++ drilled me for "clean typing" but I remember that C is much more lax about this. (void* is compatible to any pointer.)
As Garr Godfrey already said: "put your code in TMR2_DefaultInterruptHandler"
where it is recommended by the comment
// add your TMR2 interrupt custom code