There is absolute no reason to replace C code with assembler code, if C code do already the job.

But its possible to optimize the C code itself.
At first you should look on the map file to see, how many ressources eaton from any function and module. E.g., if you see, that only some XDATA was used, but still many DATA and IDATA space was unused, then you can change such XDATA variables into the internal RAM and no longer an external SRAM was needed.

Many other hints to be ecomonic with RAM and CODE space can you found in the C51-Primer.
Often to be economic with memory give also faster execution at the same time. So its also a chance to be economic with current consumption and use a slower crystal.



Peter