The common method used is to compile the various modules with their individual compilers into a common relocatable object format. Then a linker that is compatible with said object format links all the objects together into a final single executable.

In this process there is a very strong need to make sure that the calling interface conventions are the same for all the compilers. This includes the way parameters are passed and results are returned.

If you care to read my opinion on this subject....This endeavor is not worth messing around with. Embedded compilers are notorious for being both proprietary and having platform specific dependencies. This is especially true for the 8051 realm of HLLs. The concept of sharing code via special constructions or coding kludges ends up with a project environment that is a maintenance nightmare. In the long run anything you think that you may save by not porting all your code over to a single compiler environment will be offset by additional code preparation, debugging, maintenance, increased FLASH usage, run time inefficiencies and built instructions documentation.

Michael Karas