chipcon_banked_code_support.s51

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*     ***   +  +   ***                      CHIPCON                           *
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Filename:     chipcon_banked_code_support.s51
Author:
Revised:      28/11-2005
Revision:     1.0

Description:
Functions to make banked CALL and RET.

The register holding current code bank:
?CBANK

Should be defined to IAR XLINK Linker with:
-D?CBANK=xx

Copyright 2004-2005 IAR Systems. All rights reserved.

******************************************************************************/



        MODULE  ?BANKED_CODE_SUPPORT

#include "iar_common.h"

        EXTERN  ?CBANK
        EXTERN  ?RESET_CODE_BANK
        REQUIRE ?RESET_CODE_BANK
        RSEG    CSTART



;-----------------------------------------------------------------------------
;
;       Function: ?BCALL
;
;       Description: Saves the caller bank on stack, Switches to bank defined
;                    by A register and jumps to the banked function A:DPTR.
;
;       Register input:
;               DPTR:  16-bit function address
;               A:     8-bit page address
;
;       Stack:
;
;           +--------+
;           | ?CBANK | <-- SP end
;           + - - - -+
;           |  retH  | <-- SP begin
;           + - - - -+
;           |  retL  |
;           + - - - -+
;   CFA --> | xxxxxx |
;           +--------+
;
;               16-bit return address
;
;       Register output:
;               DPTR:  16-bit function-address
;               A  = 0
;
;       Stack usage: 1
;-----------------------------------------------------------------------------
   PUBLIC  ?BCALL

   cfi BLOCK ?BCALL USING cfi_common
   cfi NOFUNCTION
   cfi A undefined
   cfi CFA_MACHINE MACHINE_SP - 2

?BCALL:
   SWAP  A
   MOV   B, A
   MOV   A, ?CBANK   ; read current MEMCTR
   ANL   A, #0x30    ; mask bank bits
   SWAP  A
   PUSH  A           ; store return bank (bank number only)

   cfi CFA_MACHINE MACHINE_SP - 3

   MOV   A, ?CBANK   ; read current MEMCTR
   ANL   A, #0xCF    ; mask bank bits
   ORL   A, B        ; add new bank number to MEMCTR
   MOV   ?CBANK, A

   CLR   A
   JMP   @A+DPTR


;-----------------------------------------------------------------------------
;
;       Function: ?BRET
;
;       Description: Return from banked function.
;                    Leaves current function, Switched bank and returns to
;                    function that called ?BCALL.
;
;                    NOTE: This function will be jumped to.
;
;       Register input:
;               None
;
;       Stack input:
;
;               +------------+ <-- SP
;               |  RET bank  |
;               + - - - - - -+
;               |  RET High  |
;               + - - - - - -+
;               |  RET Low   |
;               +------------+
;
;               24-bit return address
;
;       Register output:
;               DPTR:  16-bit function-address
;               A  = 0
;
;       Stack usage: 3
;               Stack: 16-bit return address
;-----------------------------------------------------------------------------
   PUBLIC  ?BRET

?BRET:
   cfi CFA_MACHINE MACHINE_SP - 3

   MOV   B, ?CBANK   ; get current bank
   ANL   B, #0xCF    ; mask bank bits

   POP   A           ; pop bank number
   SWAP  A
   ORL   A, B        ; add the MEMCTR bits
   MOV   ?CBANK, A   ; set new bank
   cfi   CFA_MACHINE MACHINE_SP - 2

   RET

   cfi ENDBLOCK ?BCALL

   END