Re: [avr-libc-dev] [CVS commit: HEAD] document <avr/delay.h>

[René Liebscher]

Joerg Wunsch schrieb:

> I just committed the attached patch to the HEAD of CVS.
>
> As I wrote the doxygenized documentation while sitting in a train,
> without Internet access, I didn't use any of the submitted ideas
> but rather rolled my own version.  (That way, I could find a useful
> use of about an hour's worth of time. ;-)
>
> I also tried to make a stab at rolling _delay_ms and _delay_us
> macros.  The patch submitted in path #3495 looked too much like
> code duplication to me, compared to the already existing inline
> functions.  Marek's idea (in the TODO of the header file) about
> using fp math was not OK as the preprocessor can only do integer
> math.
>
>  
But the complier can do fp math !


example:
---------------
#define X (1.0/3.0)
#define Y (3.14*(X+2.7))
void test(){
   double a=3.14*(X+2.7);
}

double b=Y;
---------------
wil become after the prepocessor
---------------
# 1 "x.c"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "x.c"


void test(){
   double a=3.14*((1.0/3.0)+2.7);
}

double b=(3.14*((1.0/3.0)+2.7));
---------------
and as assembler source  ( 0x41186509 == 1092117769 
==(3.14*((1.0/3.0)+2.7))  )
---------------
       .file   "x.c"
       .arch avr2
__SREG__ = 0x3f
__SP_H__ = 0x3e
__SP_L__ = 0x3d
__tmp_reg__ = 0
__zero_reg__ = 1
       .global __do_copy_data
       .global __do_clear_bss
       .text
.global test
       .type   test, @function
test:
/* prologue: frame size=4 */
.....
/* prologue end (size=10) */
       ldi r24,lo8(0x41186509)
       ldi r25,hi8(0x41186509)
       ldi r26,hlo8(0x41186509)
       ldi r27,hhi8(0x41186509)
       std Y+1,r24
       std Y+2,r25
       std Y+3,r26
       std Y+4,r27
/* epilogue: frame size=4 */
......
       ret
/* epilogue end (size=9) */
/* function test size 27 (8) */
       .size   test, .-test
.global b
       .data
       .type   b, @object
       .size   b, 4
b:
       .long   1092117769
/* File "x.c": code   27 = 0x001b (   8), prologues  10, epilogues   9 */