hi,I write an algorithm running in cortex M0. It has some floating point multiplication.But the program always resets when encounter a floating point multiplication.And the code showed below:
for (k = 0; k < 4; k++) { tmpx = dbuffer[0] * a[k + 1]; dbuffer[k + 1] = dbuffer[k + 1] - tmpx; }
dbuffer[] and a[] are float array. tmpx is a float variable. When I debug the program, the M0 resets at line "tmpx = dbuffer[0] * a[k + 1];" .And the value of dbuffer[0] is 1429983,a[k+1] is 0.00974910986.I have tested this multiplication in a new project.And the code goes well and result is right.The test code is like below:
float a = 1429983; float b = 0.00974910986; float c; c = a* b;
So, I know M0 use softVFP. I have seen asm code such as __aeabi_fmul corresponding to my code.Could anybody tell me what's wrong with my code?Thank you very much.
Hi and welcome to the community!
I assume you use GCC, because of the '__aeabi_fmul' ... but it's still hard to guess what's wrong.
Because the second attempt works, I believe the difference might be in the way the code is built.
I will suggest that you create a new test-project, then first put your test-code in there, run it and see if it works.
If the first test works, then change the new test-project to use the code with the for-loop.
If it works now, without reseting, then I think you need to find the difference in how the code is built.
...Assuming you get it all working, you might want to consider changing for(k = 0; k < 4; k++) to for(k = 1; k < 5; k++) and then remove the '+1' from the index.
It won't really do much difference unless you've turned off optimization, but it will make your code shorter and easier to read.
Another thing to check is whether there is enough stack space allocated.
And I guess the array sizes are set to at least 5 (due to k+1)?
Thanks Joseph, I found it's stack overflow caused this weird bug. Now the code goes well.:)
hi，Jensbauer, Thanks for your reply.:)
I have solved this bug by resizing stack size. And I also learn a lot from your reply.
Does your main() end in an infinite loop ?
-If not, it should; becaues on a microcontroller, main() is not supposed to return.
I'm only asking in case your for-loop is placed inside main; if it's outside main, then a stack overflow of a single element will erase the return-address, if the array is the first (or only) variable on the stack.
This is because the return-address is the last register pushed onto the stack, thus the last element.
Note: If you have very little stack space available, then it might be helpful to save a few bytes of stack-space by adding __attribute__((naked)) in front of void main(); -but only for main or entry(), because those subroutines should never return.
When a subroutine never returns, there's no reason for it to save the registers on the stack.
Thanks,Jensbauer.
Your suggestion is very helpful. I will adopt in my project.