C51: RET_XSTK Directive

Information in this article applies to:

• C51 Version 6.01 and later

QUESTION

What does the RET_XSTK directive do?

ANSWER

The RET_XSTK directive causes the xdata reentrant stack to be used for return address. Normally, return addresses are stored on the 8051's hardware stack. This directive instructs the compiler to generate code that pops the return address from the hardware stack and stores it on the xdata reentrant stack.

You may use the RET_XSTK directive to unload return addresses from the on-chip (hardware) stack. This directive may be selectively used on the modules that contain the deepest stack nesting. If you use this directive, you must initialize the ?C_XBP reentrant stack pointer defined in the startup code.

The following example demonstrates the code generated to push and pop the return address on the pdata stack.

   1          #pragma RET_XSTK
   2          extern void func2 (void);
   3
   4          void func (void)  {
   5   1        func2 ();
   6   1      }

ASSEMBLY LISTING OF GENERATED OBJECT CODE
             ; FUNCTION func (BEGIN)
0000 120000      E     LCALL   ?C?CALL_XBP
                                     ; SOURCE LINE # 5
0003 120000      E     LCALL   func2
                                     ; SOURCE LINE # 6
0006 020000      E     LJMP    ?C?RET_XBP
             ; FUNCTION func (END)

SEE ALSO

• C51: Reentrant Functions and the Reentrant Stack Pointer
• C51: Setting the Location of the Reentrant Stack Pointer
• C51: Stack and Reentrant Stack Symbolic Names
• C51: Version 6 Release Notes

Last Reviewed: Thursday, February 25, 2021