Volatile Declarations

• Optimizer avoids memory accesses when possible

  • Code which reads from memory locations outside the scope of C ( such as a hardware register) may be optimized out by the compiler
  • To prevent this, use the volatile keyword

• Example: wait for location to have value 0xFFFF

unsigned short *ctrl; /* wait loop */

while(*ctrl != 0xFFFF); /* loop would be removed */

volatile unsigned short *ctrl; /* safe declaration */

while(*ctrl != 0xFFFF);

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