Posted on May 17, 2011 at 12:44Hi Suyongyao,
First, if you have in your program values, which never change (constants) you could declare them with ''const'' qualifier, for example:
const float a[75] = {1, 2, 3, and so on..};
In this way the linker will put them in the Flash.
However, I suppose that this is not your case. You should be aware that in STM32 (like many other embedded CPUs) a large amouth of memory is Flash and smaller part is RAM. You can not alter the Flash - at least not at the speed of the RAM. So, you can not put variables there.
The only software tricks, which you could use in this case is to limit the number of the variables you use or their size. This hardly depends on the algorithm you implement, but few guidelines are:
- reusing of temporary variables;
- modifying the algorithm to work over a part of the data (i.e. if it is possible to use an array of [75] instead of [75][75]);
- using variables of smaller size (''short'' or ''char'' instead ''float'').
If nothing of this could be used you should use an external RAM. I think than C, D and E devices allow this. You should additionaly modify the linker file (.xcl or .icf) to force it to put all or part of your variables there.
Be aware that the access to the external RAM is considerably slower than to the internal one.
BR,
Ivan
