[avr-libc-dev] [bug #17216] change to the ../util/delay.h header for increased functionality

[Bill Perry]

Follow-up Comment #4, bug #17216 (project avr-libc):

Further continue discussion from the avrfreaks thread:
http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&p=619023#619023

I think it is easy to set proper expectations for a new _delay_ns() function
through proper documentation so that people won't get a false impression that
the routines provide better precision than is actually possible

My overall desire is to have more accurate and more predictable delays for
the short delays and more importantly that a delay is never shorter than what
was requested.

The drop in alternate routines that Hans-Juergen do both of these in a fully
backward compatible way.

Long term it may be good to even re-write Han's routines to use the 
__builtin_avr_delay_cycles() function or even provide an additional builtin
delay function that take 2 arguments:
- a CPU clock rate
- a time to delay.
That way the entire functionality is handled by the compiler.









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