Zoltan Hudak / Mbed 2 deprecated Asm01

Assembly example.

Dependencies:   mbed

my_asm.s@0:c40fd5b610ee, 2019-03-09 (annotated)

Committer:
hudakz
Date:
Sat Mar 09 10:56:02 2019 +0000
Revision:
0:c40fd5b610ee
Initial release.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
hudakz 0:c40fd5b610ee 1 AREA asm_func, CODE, READONLY
hudakz 0:c40fd5b610ee 2
hudakz 0:c40fd5b610ee 3 ; Export my_asm function location so that C compiler can find it and link
hudakz 0:c40fd5b610ee 4
hudakz 0:c40fd5b610ee 5
hudakz 0:c40fd5b610ee 6 EXPORT my_asm
hudakz 0:c40fd5b610ee 7 my_asm
hudakz 0:c40fd5b610ee 8 ;
hudakz 0:c40fd5b610ee 9 ; ARM Assembly language function to set LED1 bit to a value passed from C
hudakz 0:c40fd5b610ee 10 ; LED1 gets value (passed from C compiler in R0)
hudakz 0:c40fd5b610ee 11 ; LED1 is on GPIO port 1 bit 18
hudakz 0:c40fd5b610ee 12 ; See Chapter 9 in the LPC1768 User Manual
hudakz 0:c40fd5b610ee 13 ; for all of the GPIO register info and addresses
hudakz 0:c40fd5b610ee 14 ; Pinnames.h has the mbed modules pin port and bit connections
hudakz 0:c40fd5b610ee 15 ;
hudakz 0:c40fd5b610ee 16 ; Load GPIO Port 1 base address in register R1
hudakz 0:c40fd5b610ee 17 LDR R1, =0x2009C020 ; 0x2009C020 = GPIO port 1 base address
hudakz 0:c40fd5b610ee 18 ; Move bit mask in register R2 for bit 18 only
hudakz 0:c40fd5b610ee 19 MOV.W R2, #0x040000 ; 0x040000 = 1<<18 all "0"s with a "1" in bit 18
hudakz 0:c40fd5b610ee 20 ; value passed from C compiler code is in R0 - compare to a "0"
hudakz 0:c40fd5b610ee 21 CMP R0, #0 ; value == 0 ?
hudakz 0:c40fd5b610ee 22 ; (If-Then-Else) on next two instructions using equal cond from the zero flag
hudakz 0:c40fd5b610ee 23 ITE EQ
hudakz 0:c40fd5b610ee 24 ; STORE if EQ - clear led 1 port bit using GPIO FIOCLR register and mask
hudakz 0:c40fd5b610ee 25 STREQ R2, [R1,#0x1C] ; if==0, clear LED1 bit
hudakz 0:c40fd5b610ee 26 ; STORE if NE - set led 1 port bit using GPIO FIOSET register and mask
hudakz 0:c40fd5b610ee 27 STRNE R2, [R1,#0x18] ; if==1, set LED1 bit
hudakz 0:c40fd5b610ee 28 ; Return to C using link register (Branch indirect using LR - a return)
hudakz 0:c40fd5b610ee 29 BX LR
hudakz 0:c40fd5b610ee 30 END
hudakz 0:c40fd5b610ee 31