Hi all,     I look in the port.c of the Cygnal port and see:        push _bp        …        pop _bp     What is register is that?     One more thing, in *pxPortInitialiseStack() function, line 263:        *pxTopOfStack++;     I think it must be:        pxTopOfStack++;     Am i right?

ref line 263 – looks like a mistake to me.  How did that get through?

From the SDCC manual: "_bp is the stack frame pointer and is used to compute the offset into the stack for parameters and local variables"