Go to Project -> Tool Chain Integration and add
--model-medium to both the Compiler and Linker tab command line flags!
@Maarten: Is it ok to add the --stack-auto option only to some files (ie. files containing functions were speed optimization is not the main goal) ?
What do you think about it ?
You cannot use --stack-auto on some files only. It influences the way functions outside the source file (including the libraries!) are called. You can however declare only some functions reentrant. Look in the .map file for functions that use much space in data memory. Those are good candidates.
You can also add storage classes (idata,pdata,xdata) to variables to move them outside the limited data memory.