error "unable to find a register to spill in class 'POINTER_REGS'"

Projects Programming
1

Hello,

I have encountered the strange error "unable to find a register to spill in class 'POINTER_REGS'" in the following program:

unsigned long  h[8]={0,0,0,0,0,0,0,0};
unsigned long duration[8]={0,0,0,0,0,0,0,0};
float t = 3000;
float tau = 250000;

void setup() {
}

void loop() {
    for (int i=0;i<8;i++) {
      h[i]+=(t-duration[i]);
      h[i]*=(1-t/tau);
  }
}

It is a part of a larger program, I have removed the non-erratic code to find the error. Strangely, if h and duration are not arrays, the program works:

unsigned long  h=0;
unsigned long duration=0;
float t = 3000;
float tau = 250000;

void setup() {
}

void loop() {
h+=(t-duration);
h*=(1-t/tau);
}

Any idea what could be the problem?

Thanks for answers,
Frank

2 
void fn (int i)
{
  h[i]+=(t-duration[i]);
  h[i]*=(1-t/tau);
}

and just call "fn(i);" in your loop.

3

Thank you for your answer. It works, but I have no idea why! Also, if I change the definition of h slightly like this:
```
*unsigned long  h[8]={0,0,0,0,0,0,0,0};
unsigned long duration[8]={0,0,0,0,0,0,0,0};
float t = 3000;
float tau = 250000;

void setup() {
}

void loop() {
    for (int i=0;i<8;i++) {
      h[i]+=(t-duration[i])-(h[i]t/tau);
  }
}
```
then it works, but why???
Cheers,
Frank

4
5

Shouldn't the compiler automatically decide correctly which variables are stored in memory or in a register and if necessary transfer them (spilling and filling)? Why does the error occur? The program is very small, so the resources are not short.

6

I don't know - I'm not a compiler writer, but mixed indexing, floats and longs is pretty register-intensive.

7

OK, thanks for your answers!