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Re: [avr-libc-dev] Better Interrupt Macro

From: Dean Camera
Subject: Re: [avr-libc-dev] Better Interrupt Macro
Date: Mon, 27 Nov 2006 08:20:13 +1100

Will this allow for the following syntax:

  ISR(VectorName, ISR_NOBLOCK)
  // Code goes here

Wouldn't this set both the 'interrupt' and 'signal' attributes at the
same time?

Yes indeed, very astute. the reason for declaring the ISR macro with the ISR_NOBLOCK (signal) is for backwards compatibility. If no second argument, the SIGNAL attribute is applied.

I have discovered in testing that having the signal as well as another ISR-related attribute specified at the same time works correctly and gives the expected output. If ISR_NOBLOCK is specified, then the resultant ISR contains a SEI as expected, if ISR_NAKED is specified, then the resulting code lacks a prologue or epilogue. Since it works fine, I don't think it is a problem. As a bonus, the SIGNAL attribute forces GCC to spell-check the vector name.

The only real issue with my macros as I can see it is a lack of a way to create an ISR_EMPTY equivalent. The only way I can think of doing this would be to create a "ISR_return()" macro ( #define ISR_return() __asm__ __volatile__ ("reti" ::); ) and then in the docs tell the user the correct way of doing so would be:

ISR(VectorName, ISR_NAKED)

Subject to individual's coding style, of course. I actually see this as a plus; the "ISR_return()" macro is in a similar style to the sei() and cli() macros, and so would be useful to those creating their own (non-empty) ISR_NAKED routines also. Although If the current convention was to be adhered to, the macro name would be "reti();", I suppose.


- Dean

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