144 |
Chapter 5. Assembler Macros |
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Repeating Blocks
Ax51 provides the ability to repeat a block of text within a macro. The REPT, IRP, and IRPC directives are used to specify text to repeat within a macro. Each of these directives must be terminated with an ENDM directive.
REPT
The REPT directive repeats a block of text a fixed number of times. The following macro:
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DELAY |
MACRO |
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;macro definition |
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REPT |
5 |
;insert 5 NOP instructions |
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NOP |
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ENDM |
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;end REPT block |
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ENDM |
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;end macro definition |
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inserts 5 NOP instructions when it is invoked. |
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Example |
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5 |
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NOP |
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NOP |
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NOP |
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NOP |
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NOP |
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Keil Software — A51/AX51/A251 Macro Assembler and Utilities |
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IRP
The IRP directive repeats a block once for each argument in a specified list. A specified parameter in the text block is replaced by each argument. The following macro:
CLRREGS |
MACRO |
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; macro definition |
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IRP |
RNUM, |
<R0,R1,R2,R3,R4,R5,R6,R7> |
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MOV |
RNUM, #0 |
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ENDM |
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; end IRP |
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ENDM |
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; end MACRO |
replaces the argument |
RNUM |
with R0, R1, R2, … R7. |
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It generates the following code when invoked:
MOV |
R0, #0 |
MOV |
R1, #0 |
MOV |
R2, #0 |
MOV |
R3, #0 |
MOV |
R4, #0 |
MOV |
R5, #0 |
MOV |
R6, #0 |
MOV |
R7, #0 |
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146 |
Chapter 5. Assembler Macros |
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IRPC
The IRPC directive repeats a block once for each character in the specified argument. A specified parameter in the text block is replaced by each character. The following macro:
DEBUGOUT |
MACRO |
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; macro definition |
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IRPC |
CHR, <TEST> |
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JNB |
TI, $ |
; wait for xmitter |
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CLR |
TI |
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MOV |
A,#'CHR' |
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MOV |
SBUF,A |
; xmit CHR |
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ENDM |
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; end IRPC |
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ENDM |
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; end MACRO |
replaces the argument CHR with the characters T, E, S, and T and generates the following code when invoked:
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JNB |
TI, $ |
; WAIT FOR XMITTER |
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CLR |
TI |
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MOV |
A,#'T' |
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MOV |
SBUF,A |
; XMIT T |
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JNB |
TI, $ |
; WAIT FOR XMITTER |
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CLR |
TI |
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MOV |
A,#'E' |
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MOV |
SBUF,A |
; XMIT E |
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JNB |
TI, $ |
; WAIT FOR XMITTER |
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CLR |
TI |
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MOV |
A,#'S' |
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MOV |
SBUF,A |
; XMIT S |
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JNB |
TI, $ |
; WAIT FOR XMITTER |
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CLR |
TI |
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MOV |
A,#'T' |
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MOV |
SBUF,A |
; XMIT T |
Keil Software — A51/AX51/A251 Macro Assembler and Utilities |
147 |
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Nested Definitions
Macro definitions can be nested up to nine levels deep.
Example
L1 |
MACRO |
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LOCAL |
L2 |
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L2 |
MACRO |
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INC R0 |
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ENDM |
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MOV |
R0, #0 |
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L2 |
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ENDM |
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The macro L2 is defined within the macro definition of L1. Since the LOCAL directive is used to define L2 as a local symbol, it is not visible outside L1. If you want to use L2 outside of L1, exclude L2 from the LOCAL directive symbol list.
Invocation of the L1 macro generates the following:
MOV |
R0, #0 |
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INC |
R0 |
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Nested Repeating Blocks |
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You can also nest repeating blocks, specified with the REPT, IRP, and IRPC |
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directives. |
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Example |
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PORTOUT |
MACRO |
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; macro definition |
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IRPC |
CHR, <Hello> |
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REPT |
4 |
; wait for 4 cycles |
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NOP |
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ENDM |
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; end REPT |
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MOV |
A,#'CHR' |
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MOV |
P0,A |
; write CHR to P0 |
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ENDM |
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; end IRPC |
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ENDM |
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; end MACRO |
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This macro nests a REPT block within an IRPC block.