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Re: [avr-libc-dev] interrupt enable functions

From: E. Weddington
Subject: Re: [avr-libc-dev] interrupt enable functions
Date: Wed, 07 Aug 2002 16:41:00 -0600

On 8 Aug 2002 at 0:09, Joerg Wunsch wrote:

> While i've fixed Ted's FIXME item above, how do others feel about
> these functions?  I don't value them much because they always clobber
> the respective interrupt enable register completely, so when working
> with more than one of each respective interrupt source (timer vs.
> external), one has to manually keep track about which interrupt
> sources are currently enabled.
> IMHO, we should deprecate those interfaces, and write a real "enable/
> disable one interrupt source" interface instead, like
> timer_enable_int(int bit)
> {
>  TIMSK |= BV(bit);
> }
> timer_disable_int(int bit)
> {
>  TIMSK &= ~BV(bit);
> }
> Opinions?

I agree in that those interfaces should be deprecated and should 
write a real "enable/disable one interrupt source".

However, in the example above, the programmer is still required to 
know the structure of the TIMSK register and ensure that s/he is 
setting the correct bit.

As a counter example, it would require a bit more effort but could be 
implemented in macros:

// Example for ATmega128
#define timer_1_IC_interrupt_enable()           (TIMSK |= BV(5))
#define timer_1_IC_interrupt_disable()  (TIMSK &= ~BV(5))
#define timer_1_OCA_interrupt_enable()  (TIMSK |= BV(4))
#define timer_1_OCA_interrupt_disable() (TIMSK &= ~BV(4))
#define timer_1_OCB_interrupt_enable()  (TIMSK |= BV(3))
#define timer_1_OCB_interrupt_disable() (TIMSK &= ~BV(3))

These macros take care of a single source interrupt.

This could be taken a step further and the numbers for the bit values 
could be gotten from the #defines in the processor-specific header 
files (i.e. iom128.h, and for that matter these macros could be 
placed in the processor-specific files.

Also this brings up another question, in your example Joerg, you do 
direct-assignment to the registers. I prefer that as well, using the 
"new headers" from Chris Morse and Don Carveth. This method is used 
frequently in other cross-compilers (at least on Windows). How about 
deprecating the io macros? The compiled output is the same for direct-
assignment vs. macros, and the assignment is easier to read and 
understand. See the file newhdrs.txt from the above authors for 


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