What is the difference between a static global and a static volatile variable?

Question

I have used a static global variable and a static volatile variable in file scope,

both are updated by an ISR and a main loop and main loop checks the value of the varia

Answer 1

The "volatile" keyword suggests the compiler not to do certain optimizations on code involving that variable; if you just use a global variable, nothing prevents the compiler to wrongly optimize your code.

Example:

#define MYPORT 0xDEADB33F

volatile char *portptr = (char*)MYPORT;
*portptr = 'A';
*portptr = 'B';

Without "volatile", the first write may be optimized out.