The compiler should be smart enough that it doesn't need us to make things
simpler for it. The important point is readability so the next person who
has to maintain the code is able to figure out what is going on. Heck, I
might have to come back to my own code 6 months to a year later and want to
make it so I can quickly understand it again.
One minor point, though. If you write your macro as:
#define P5_ALARM_ENABLE (1<<5)
then the precompiler is going to put the "(1<< 5) into your code which is
going to put a 1 into a register and then shift it over before it even
applies the mask, an operation that is going to take several cycles. I
would think it would be better if you defined things with your "or" case:
#define P5_ALARM_ENABLE (0x20)
which should execute more efficiently. Or is the optimizer smart enough to
recognize this too? I don't know, I haven't looked at the code that these
would generate.
I'll go back to lurking now.
Jeff
On 7/12/06, Peter Jansen <[email protected]> wrote:
> // Alarm output
> #define ALARMENABLE port2.out.pin5 = 1
> #define ALARMDISABLE port2.out.pin5 = 0
I prefer to make it simpler for the compiler and generally define things
like
#define P5_ALARM_ENABLE (1<<5) /* or 0x20 */
#define P5_ALARM (1<<6) /* or 0x40 */
and use it in the code like
P5_OUT |= P5_ALARM_ENABLE;
P5_OUT &= ~P5_ALARM_ENABLE;
then this also works,
P5_DIR |= P5_ALARM_ENABLE; /* make the ALARM_ENABLE pin an output */
and
if ((P5_IN & P5_ALARM) != 0)
{
printf("Alarm set\n");
}
or
if ((P5_OUT & P5_ALARM_ENABLE) != 0)
{
printf("Alarm enabled\n");
}
Ok, maybe its not as simple to write the main code as BitSet, BitReset
etc macros, bit its always obvious what is going on, and generally
compiles down to compact code, you do have to know how the bits work,
but as an embedded programmer maybe that is a good thing.
As usual many ways to skin a cat.
Regards,
--
Peter Jansen
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