ISR global variable change

[CCS_neophite]

I need to modify a variable down in an ISR routine. Do I need to use a pointer to allow the routine to access the variable? Thanks.

[Douglas Kennedy]

Short answer is no.
Ex

#include...
#fuses...

int8 myownglobal;
#int_xxx
myownisr()
{
myownglobal=99;
}
main()
{
while(1);
}

[valemike]

Suppose we had an "unsigned long", i.e. anything bigger than a byte.

I would find it safer to disable interrupts when reading that variable, or especially changing it, while not in an ISR. Reason being, an interrupt might occur right in the middle of that multi-byte manipulation operation.

Maybe i'm being paranoid, but this practice arose back in my days of RTOSes, semaphores, globals, tasks accessing the same variable, etc.

[Douglas Kennedy]

valemike is right with the caution about reading or writing variables that are more than int8 in length that are assigned within an isr. A possible method to mitigate this is to have the globals that are updated by isr code read inside a function
Ex template

int16 myisrglobalreader()
{
int16 temp;
disable_interrupts(the interrupt that writes to global);
temp=myglobalvar;
enable_interrupts(the interrupt that writes to global);
return temp;
}
main()
{
int16 value;
value=myisrglobalreader();
while(1);
}