I have developed a small Single Board computer, with a few customizations.

I am well versed in Assembly programming for 8052, but not for C. I have written driver functions for the devices on the board in assembly and this "BIOS" will be burned in the on-chip 20KB (89c55) eeprom as a simple monitor program. Upon startup, it will initialize some variables, a custom protocol stack and then jump to user program rom (at 8000h) address.

I want to write user codes in C (Keil), but in SMALL and / or COMPACT modes, since C uses the internal data ram for stack and other variables, but this might clash with the BIOS variables that are at fixed internal-ram addresses.

Secondly, the BIOS program will initialize stack to reside in the extra 128-bytes ram (80h and above) while it is not certain where C will put the stack to start at.

Can anyone guide me as to how this situation can be avoided or controlled ?