Hello, If anyone can provide a quick reference.......... Is sei() an AVR assembler macro ?
It enables interrupts.
reference from AVR LibC
#define sei ( )
Enables interrupts by setting the global interrupt mask. This function actually compiles into a single line of assembly, so there is no function call overhead. However, the macro also implies a memory barrier which can cause additional loss of optimization.
In order to implement atomic access to multi-byte objects, consider using the macros from <util/atomic.h>, rather than implementing them manually with cli() and sei().
GoForSmoke: reference from AVR LibC
Many thanks, exactly what I was trying to locate