On Mon, 2009-02-16 at 23:37 +0100, Georg-Johann Lay wrote:
> distance = =895*distance;
See my followup message about the typo.
distance = 895*distance.
>
> [...]
>
> > 895*distance generates a call to __mulsi3, multiplying r25:22 by r21:18
> > and returning the result in r25:22.
> >
> > However, I cannot find where r21:18 are set in the code. Looking at the
> > output of avr-gcc -S, I cannot find any of r18:21.
>
>
The compilable source is 3700 lines. I can post it if necessary.
I think the following will demo the problem
1. Create the two files, as below.
2. Compile with
avr-gcc -mmcu=atmega32 -Wall -Wmissing-prototypes -Os \
-fno-strict-aliasing range.c global_var.c -o range.elf
3. avr-objdump -d range.elf
===== range.c =======================
#include <avr/io.h> // port definitions
#include <inttypes.h>
extern volatile uint8_t range_new;
extern volatile uint8_t range_local;
extern volatile uint8_t range_count;
extern volatile uint8_t range_local_ovfl;
extern volatile uint8_t disp_range_count;
extern volatile uint8_t disp_range_ovfl;
extern volatile uint8_t range_ovfl;
int main() {
while(1) {
// if we have new range data, process it
if (range_new == 1) {
{
uint32_t distance = range_local_ovfl<<8;
distance += (uint32_t)range_count;
distance = 2345*distance;
distance = distance >> 16;
range_local = (uint8_t)(distance - 4)&0xff;
}
disp_range_count = range_count;
disp_range_ovfl = range_ovfl;
}
return 0;
}
}
==== global_var.c ===================
#include <avr/io.h> // port definitions
#include <inttypes.h>
volatile uint8_t range_new;
volatile uint8_t range_local;
volatile uint8_t range_count;
volatile uint8_t range_local_ovfl;
volatile uint8_t disp_range_count;
volatile uint8_t disp_range_ovfl;
volatile uint8_t range_ovfl;
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