The KEIL compiler supports simulated stack-based parameter passing. It is no less efficient that maintaining a base pointer and pushing and popping off of the hardware stack. The stack may be maintained in IDATA space, PDATA space, or XDATA.

The PDATA stack is a really good choice since it uses the MOVX @R0 and MOVX @R1 instructions to access 256 bytes of an XDATA page. It generates far less code than a stack in XDATA and only byte or two more than the IDATA stack.

You declare functions as follows:

int func (int arg1, int arg2, int arg3) reentrant
{
}

It's pretty straight forward after that.

Jon Ward
Keil Software