ARM Assembly, register not being set to 0?
start
read
BL getkey ; read key from console
CMP R0, #0x0D ; while (key != CR)
BEQ endRead ; {
BL sendchar ; echo key back to console
CMP R0, #' ' ; if (ro = ' ')
BNE nocount ;{
ADD R7, R7, #1 ; r7 += 1
LDR R4, =0 ; r4 = 0
nocount ;}
MOV R6, R0 ; Store input in R6
SUB R6, R6, #'0' ; Convert from decimal to hex
MULS R4, R5, R4 ; If there is another input, multiply total by 10
ADDS R4, R4, R6 ; Add the input to the total
ADD R8, R4, R8 ;sum
B read
endRead
end
stop B stop
END
Hi, I'm trying to have my code so when there is a space entered into the console, 1 will be added to R7 and R4 will be set to 0.
When a space is added, R4 is set to 0xFFFFFFF0, but when I add '5' to this, I get 0xFFFFFFF65. I expect to just get 0x00000005. This is weird, because when I put the same command outside the compare, it works. Any help is appreciated, thanks.
Also I want r8 to be the sum of numbers entered, it doesn't seem to be working properly, can anyone tell me why?
Michael4 Answers
Have you explored conditional execution ADD, etc?
Assumes: ARMv7 My machine = Linux raspberrypi 4.4.26-v7+ #915 SMP Thu Oct 20 17:08:44 BST 2016 armv7l GNU/Linux
cmp r0, #0x20 // white space - space char
addeq r7, r7, #1 // conditional add
eoreq r4, r4 // conditional zero
InfinitelyManicLDR R4, =0
doesn't assign zero to the register. It loads the register from the memory address 0. Use
MOV R4, #0
instead.
Seva AlekseyevRegarding the summation of the numbers; please the example below of a simple decremented loop where the sum of each number is added to R1. Hope this helps.
main: nop
eor r2, r2
mov r1, #0xf
1:
add r2, r2, r1
bl write
subs r1, #1
bne 1b
OUTPUT:
15 15
14 29
13 42
12 54
11 65
10 75
9 84
8 92
7 99
6 105
5 110
4 114
3 117
2 119
1 120
Sorry everyone, the code is correct, it was just not in the right position, thanks everyone!
Seamus WUser contributions licensed under CC BY-SA 3.0