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Technical Support On-Line Manuals Cx51 User's Guide |
Large Model ExampleIn the large model, parameters passed in fixed memory locations are stored in external data memory. The parameter passing segment for variables is located in the xdata area. The following are two assembly code examples. The first shows you how the example function is called from assembly. The second example displays the assembly code for the example function. Calling a C function from assembly.
EXTRN CODE (_function) ; Ext declarations for function names
EXTRN XDATA (?_function?BYTE) ; Start of transfer for local vars
EXTRN BIT (?_function?BIT) ; Start of transfer for local bit vars
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MOV R6,#HIGH intval ; int a
MOV R7,#LOW intval ; int a
MOV R5,#charconst ; char b
SETB ?_function?BIT+0 ; bit c
MOV R0,#?_function?BYTE+3 ; Address of 'v_d' in the passing area
MOV A,longval+0 ; long d
MOVX @DPTR,A ; Store parameter byte
INC DPTR ; Increment parameter passing address
MOV A,longval+1 ; long d
MOVX @DPTR,A ; Store parameter byte
INC DPTR ; Increment parameter passing address
MOV A,longval+2 ; long d
MOVX @DPTR,A ; Store parameter byte
INC DPTR ; Increment parameter passing address
MOV A,longval+3 ; long d
MOVX @DPTR,A ; Store parameter byte
MOV C,bitvalue
MOV ?_function?BIT+1,C ; bit e
LCALL _function
MOV intresult+0,R6 ; Store int
MOV intresult+1,R7 ; Retval
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Assembly code for the example function:
NAME MODULE ; Name of the program module
?PR?FUNCTION?MODULE SEGMENT CODE ; Seg for program code in 'functions'
?XD?FUNCTION?MODULE SEGMENT XDATA OVERLAYABLE
; Seg for local vars in 'function'
?BI?FUNCTION?MODULE SEGMENT BIT OVERLAYABLE
; Seg for local bit vars in 'function'
PUBLIC _function, ?_function?BYTE, ?_function?BIT
; Public symbols for C function call
RSEG ?XD?FUNCTION?MODULE ; Segment for local variables
?_function?BYTE: ; Start of the parameter passing seg
v_a: DS 2 ; int variable: v_a
v_b: DS 1 ; char variable: v_b
v_d: DS 4 ; long variable: v_l
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.; Additional local variables from 'function'
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RSEG ?BI?FUNCTION?MODULE ; Segment for local bit variables
?_function?BIT: ; Start of the parameter passing seg
v_c: DBIT 1 ; bit variable: v_c
v_e: DBIT 1 ; bit variable: v_e
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. ; Additional local bit variables
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RSEG ?PR?FUNCTION?MODULE ; Program segment
_function: MOV DPTR,#?_function?BYTE+0 ; Special function prolog
MOV A,R6 ; and epilog is not
MOVX @DPTR,A ; necessary. All vars
INC R0 ; can immediately be
MOV A,R7 ; accessed.
MOVX @DPTR,A
INC R0
MOV A,R5
MOVX @DPTR,A
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MOV R6,#HIGH retval ; Return value
MOV R7,#LOW retval ; int constant
RET ; Return
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