what is difference b/w extern & volatile variable??
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Answer Posted / anonimos
volatile variables are used on RT Embedded systems to
interface a physical memory mapped/IO mapped cell on the
computer board (volatile pointer).
Example define IO port:
#define PortA (*(volatile unsigned char *)0x3b)
unsigned char inputValue=PortA;
optimization may attempt to perform paging to hard drive of
to cache or even CPU registers so when reading from the
physical location in Mem/IO space the program will actually
read old value that was paged/cached by optimization
algorithm of the computer/board, even after the Input
changed on this Memory/IO cell.
volatile instruct the compiler to prevent optimization by
caching to registers/cache.
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