RTX51 TINY: SAVING AND RESTORING XDATA BANKING INFORMATION

Information in this article applies to:

RTX51 Tiny Version 2.00

QUESTION

I am using the Keil PK51, RTX51 Tiny Version 2, and far memory to access 4 banks of SRAM. The XDATA Banking is configured in the XBANKING.A51 file. I need to save and restore the XDATA banking information when RTX51 Tiny performs a task switch.

I'm using code banking (configured via L51_BANK.A51) and that works just fine with RTX51 Tiny. The XDATA Banking information should be just as easily saved. Can you point me in the right direction so that I can modify CONF_TNY.A51 myself?

ANSWER

Yes. It is easy to add code to save and restore the XDATA banking details. You must modify the CONF_TNY.A51 and OS_CREATE.A51 files.

You should add the XDATA banking save/restore code at the same location where the CODE_BANKING support is introduced via the IF (CODE_BANKING <> 0) directives.

CONF_TNY.A51

There are 2 occurrances of the code sequence that saves the bank information in CONF_TNY.A51. You should add the XDATA banking save/restore code to both. For example:

IF (CODE_BANKING <> 0)
                PUSH    ?B_CURRENTBANK
ENDIF

; *** Add code here to save the
; *** XDATA banking port value to the stack

The code to restore the XDATA banking port must be inserted in the following code sequence:

NoEvent:        CLR     ACC.B_RUN       ; Clear RUN bit
                XCH     A,@R0
                SETB    EA

                ANL     A,#K_RUN
                ORL     AR7,A

; *** Add code here to restore the
; *** XDATA banking port value from the stack

IF (TIMESHARING <> 0)
  IF (CODE_BANKING)
            POP ACC
                CALL    ?B_RESTORE_BANK
  ENDIF
                CLR     ?RTX_TS_DELAY
                RET

OS_CREATE.A51

You must modify the OS_CREATE.A51 source file to adjust the stack layout. There are several places where the stack is adjusted as shown below:

$IF (CODE_BANKING)
                DEC     R1

; *** Add a DEC R1 for each byte
; *** you save on the stack
$ENDIF

and

$IF (CODE_BANKING)
                INC     @R0

; *** Add an INC R1 for each byte
; *** you save on the stack
$ENDIF

You must add code to the following to select the default XDATA bank that is selected when the task starts.

$IF (CODE_BANKING)
EXTRN   DATA    (?B_CURRENTBANK)
                INC     R0
                MOV     A,?B_CURRENTBANK     ; Set the initial code bank
                MOV     @R0,A

; *** Add code for each byte restored
; *** that selects the XDATA banking port
;           INC   R0
;           MOV   A,#0  ; default XDATA banking port
;           MOV @R0,A

Last Reviewed: Tuesday, November 05, 2002