jim hamblen / Mbed 2 deprecated C_to_asm

An example calling assembly from C. Assembly source is in a *.s file

Dependencies:   mbed

my_asm.s@0:ef242c5b2981, 2010-09-29 (annotated)

Committer:
4180_1
Date:
Wed Sep 29 02:44:55 2010 +0000
Revision:
0:ef242c5b2981

        

        
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    AREA asm_func, CODE, READONLY





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 ; Export my_asm function location so that C compiler can find it and link





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    EXPORT my_asm





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my_asm





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; ARM Assembly language function to set LED1 bit to a value passed from C   





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; LED1 gets value (passed from C compiler in R0)





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; LED1 is on GPIO port 1 bit 18





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; See Chapter 9 in the LPC1768 User Manual





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; for all of the GPIO register info and addresses





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; Pinnames.h has the mbed modules pin port and bit connections





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;





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; Load GPIO Port 1 base address in register R1 





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    LDR     R1, =0x2009C020 ; 0x2009C020 = GPIO port 1 base address





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; Move bit mask in register R0 for bit 18 only





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    MOV.W   R2, #0x040000   ; 0x040000 = 1<<18 all "0"s with a "1" in bit 18





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; value passed from C compiler code is in R0 - compare to a "0" 





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    CMP     R0, #0          ; value == 0 ?





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; (If-Then-Else) on next two instructions using equal cond flag





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    ITE EQ





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; STORE if EQ - clear led 1 port bit using GPIO FIOCLR register and mask





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    STREQ   R2, [R1,#0x1C]  ; if==0, clear LED1 bit





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; STORE if NE - set led 1 port bit using GPIO FIOSET register and mask





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    STRNE   R2, [R1,#0x18]  ; if==1, set LED1 bit





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; Return to C using link register (Branch and change instruction set)





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    BX      LR





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    END