The __persistent type qualifier is used to indicate that
variables should not be cleared by the runtime startup code by having them stored in a
different area of memory to other variables.
By default, C variables with static storage duration that are not explicitly initialized are cleared on startup. This is consistent with the definition of the C language. However, there are occasions where it is desired for some data to be preserved across a Reset.
For example, the following ensures that the static local object,
intvar, is not cleared at startup:
void test(void)
{
static __persistent int intvar; /* must be static */
// ...
}