ColdFire/68K Microcontrollers and ProcessorsのトピックFloat calculating problems with 548x

Float calculating problems with 548x

Poloni — Tue, 07 Sep 2010 01:13:59 GMT

Hi there!

I'm with a problem using LTIB 20080811, kernel 2.6.25 with compiler 4.2-125. I wrote a program that make simple calculations.

The source code follows below:

#include <stdio.h>

#include <math.h>

static float misc_calculations();

int main(int argc, const char * argv[])

{

float reference = misc_calculations();

printf("Reference: %f\n", reference);

while (1)

{

float value = misc_calculations();

if (value != reference)

printf("Value: %f\n", value);

}

static float misc_calculations()

{

const float float_a = .2;

const float float_b = .152;

float result = 0.0;

result = float_a – float_b;

return result;

}

When I execute two instances, the behavior is very strange.

Result:

Value: 2.411886
Value: 156705821244071112293643497228883460096.000000
Value: 15.301361
Value: -174085336471250674867240960.000000
Value: 1.250146
Value: 2.771876
Value: -2.302972
Value: 2.567792
Value: -0.519974
Value: -1.523481
Value: 0.132017
Value: 0.572767
Value: -0.011594
Value: 2.511886
Value: -1.523481
Value: 7.476519
Value: -174085336471250674867240960.000000
Value: 557824153357922598912.000000
Value: 156705821244071112293643497228883460096.000000
Value: 1.511886
Value: -2.579387
Value: 0.998819

This problem occurs when I run two process. Only one process, it's executed OK, but when you execute a top program, the errors also appear.

In kernel, I checked the definition CONFIG_FPU. I created the definition, but the result is still the same. For me, the problem is concurrency between process and the kernel is not saving the context.

I used another options as -msoft-float, -mcfv4e and -mcpu=5485.

Anyone ever had this problem?

Regards,

Leandro dos Santos

Re: Float calculating problems with 548x

kwong — Thu, 11 Nov 2010 01:12:43 GMT

Hi, I think I've just run into the same problem. I'm using the a slightly modified 2.6.25 kernel from Freescale on a mcf5472 processor. If I load down the processor with other tasks, my application that performs the floating point math returns inconsistent results. If I trim down the number of processes to the bare minimum, my application starts running more reliably.

I looked inside the source code for the kernel, and it looks like the "resume" block within the arch/m68k/coldfire/entry.S file is missing all of the floating point context switching code that existed in the 2.6.10 kernel.

I'm going to try re-adding that code today to see if it makes a difference. Can anyone else provide any feedback about this in the meantime?

Thanks

Re: Float calculating problems with 548x

Poloni — Wed, 24 Nov 2010 19:01:07 GMT

Hi kwong!

Check the new version of LTIB (2010). In this distribution (kernel 2.6.29) this problem is solved.

I merged the kernel 2.6.29 and solved the problem in the kernel 2.6.25. If you want, I can send my patch.

Regards,

Leandro