[Bug target/20288] AVR assignment of a value through a 16 bit pointer generates out of order code

[schlie at comcast dot net]

------- Additional Comments From schlie at comcast dot net  2005-03-03 19:47 -------
(In reply to comment #6)
Nope, these are peripheral i/o registers, and like any pheripheral interface may have
access sequence requirements which need to be satsifyed within it's driver. These
perpheral register's access sequence requirements have nothing to do with the avr's
ISA or impled compiler requirments, just simply the conventions which need to be
followed when attempting to access manipulate dynamically active 16-bit counter
values through a pair of 8-bit i/o registers (which happen to be mapped in data
address space, which isn't an uncommon, but implies nothing otherwise, other than
you shouldn't assume that the compiler need sequence indirect access to arbitrary
multi-word/byte transactions data to satisfy a peripheral's interface sequence
that's the job of the author of the it's interface driver to guarantee; and by the way,
you still need to disable interrupts if an interrupt routine may access the same
registers, as all the sequence does is read/write upper 8-bit latched value when
ever the lower 8-bit value is accessed, so therefore if you write the high value,
get an interupt which writes both, then write the low value, you get the interrupt
routines high value, combined with your new low value written, which isn't likely
what you want.




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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20288