I am trying to make a loop that will add user inputted integers into an array until it fills the array. Every time I typed in a value, QTSPIM spits out 268501016 which I assume to be some random value stored in an register.
To test if my program was going through the whole loop, I added a call to an ascii line when the program reached the branch portion of my beq. The program seemed to be branching even if the values were not (at least to my understanding) equal.
.data
array1: .space 24
str1: .ascii "Type in numbers:"
str2: .ascii "Reached Terminate"
.text
main:
li $t2, 5
li $t3, 0
loop1:
beq $t3, $t2, terminate #branch if equal
la $a0, str1
syscall
ori $v0, $0, 5 #instruction to store user input in v0
syscall #get user input and store it in v0
la $t4, array1 #load the address of the array
addu $t0, $0, $v0 #add v0 (our user input) to $t0
sw 0($t4), t0 #stores the value in $t4 to our array
addi $t3, $t3, 1 #add 1 to t3 (incrementing the counter)
addi $t4, $t4, 4 $add 4 to increment the array 4 bits to the next array slot
jal loop1
terminate:
la $a2, str2 #load the string to check when the program reaches terminate
syscall
ori $v0, $0, 10 # end the program
syscall
The only thing I can think is that my jump call is not going back to loop1, but if this is the case I am unaware how to fix that.
This is 32 bit MIPS code.
You're not setting up the registers properly before the syscalls.
Here there should be an li $v0, 4 before syscall:
la $a0, str1
syscall
If we assume that you're trying to print str2 here, there should be an li $v0, 4 before the syscall, and $a0 should be used instead of $a2:
la $a2, str2 #load the string to check when the program reaches terminate
syscall
This should be sw $t0, 0($t4), not the other way around:
sw 0($t4), t0
This should be j, not jal (jal is used for function calls):
jal loop1
Related
I am new to MIPS and I wrote a basic format of what I think the code from the C file I wrote is the equivalent to of the MIPS.
My assignment is to convert the following C file which I wrote into a direct translation of what the MIPS is supposed to be. My current C code is :
#include <stdio.h>
int d2b(int d)
{
if(d == 0)
{
return;
}
else
{
return (d %2 + 10 * d2b(d/2));
}
}
int main()
{
int d = 99;
int b;
b = d2b(d);
printf("Input => %d \n", d);
printf("Output => %d ", b);
return;
}
So far I have the following :
.data
msg1 .asciiz “Number is “
msg2 .asciiz “\nConverted to \n“
.text
.globl main
main:
li $v0, 4
la $a0, msg1
syscall
li $v0, 5 #Exit syscall
syscall
add $a0, $v0, $zero
jal fact
add $a0, $v0, $zero
li $v0, 1
syscall
li $v0, 10
la $a0, msg2
syscall
fact:
li $t0 0 #load 0
beq $a0, $t0, skip #test n
li $v0 0
jr $ra
skip:
subu $sp, $sp, 32
sw $ra 20($sp)
sw $fp, 16($sp)
addiu $fp, $sp, 28
sw $a0, 0($fp) #save n
li $t1 2 #load 2
divu $a0 $t1 #n / 2
mfhi $t2 #remainder
mflo $t3 #quotient
move $a0, $t3 #n = quotient
addi $v0, $a1, 10
jal fact
lw $a0, 0($fp) #restore n
multu $v0, $a0
lw $ra, 20($sp)
lw $fp, 16($sp)
addiu $sp, $sp, 32
jr $ra
My main problem is not knowing how to use syscall and not really understand a recursive function in MIPS. Please point out my mistakes and errors!
your MIPS syscalls are in this section
li $v0, 4
la $a0, msg1
syscall
li $v0, 5 #Exit syscall
syscall
add $a0, $v0, $zero
jal fact
add $a0, $v0, $zero
li $v0, 1
syscall
li $v0, 10
la $a0, msg2
syscall
They are commented incorrectly
In a MIPS syscall $v0 holds the "syscall function" or in English, the service you want the operating system to perform. There's a table of them here.
$a0 will hold the first parameter passed to the call. To set this parameter, one technique is to add the input value to zero storing the result into $a0 That's why you have so many lines like this
add $a0, $v0, $zero # this adds $v0 to the number zero and storing in $a0
Finally, the syscalls you are using are (4 => print String, 5 => read integer, 1 => print integer, and 10 => exit)
So a properly commented example of your code would be
la $a0, msg1 # load string as parameter
li $v0, 4 # load operation "print string"
syscall # request "print string" for msg1
li $v0, 5 # load operation "read integer"
syscall # request "read integer"
add $a0, $v0, $zero # load the read integer into $a0
jal fact
add $a0, $v0, $zero # load the value of $v0 into $a0
li $v0, 1 # load operation "print integer"
syscall # request "print integer"
As you can see, my confusion comes not from your ability to use syscalls, but from your description of what you think you are using the syscalls to do.
You state you want to print a binary number like 01001010 from a decimal input. This typically involves breaking the decimal number down, in a loop, printing out a zero or one in each of the binary number places. As this would require a loop for each placeholder in the binary number, it doesn't seem that a single call to "print integer" would be possible (unless the input was limited to only the decimal '1' and '0', or the input is limited to such a small number that it's binary representation, represented in decimal format is less than max_int).
So for an input of 5, the desired output would be 101, and that would be 3 calls to print, in the order of '1', '0', '1'. I believe this approach of printing the digits in a loop will give you greater success, and will permit you to print every positive decimal number inputted.
In short, I think your command of syscall is fine, but you're still struggling with how to do loops and solve problems in assembly. Try to figure out how you would determine the digits in the needed order by hand, using a pencil and paper, and then attempt to code that into your program.
So I am using MIPS trying to read in several strings entered by a user and then print them, but I am not getting the behavior I expect.
I want to take in 4 bytes of user input (4 characters essentially). In my loop I use the letter 'D' as a signal to exit. The problem is, no matter what I input, when I try to print the very first input later (or even the second, or the third), all I get printed out is the letter 'D' that was used to exit (which should be the last value of the array no?).
.data
mem: .space 256 #256 bytes of space for input
inst .space 5
.text
la $s1, mem #s1 used to take input
la $s2, 0($s1) #Pointer to base address of memory
jal readLoop #Read input loop
lw $a0, 0($s2) #Attempt to read very first saved input
li $v0, 4
syscall
li $v0, 10 #End program
syscall
readLoop:
li $v0, 8 #read string
la $a0, inst #location of input memory
addi $a1, $zero, 5 #length of buffer
syscall
lb $t2,($a0) #used to exit loop
sw $a0, 0($s1) #store input into memory
addi $s1, $s1, 4 #increment memory by 4 bytes
li $t1, 'D'
bne $t2, $t1, readLoop #exit loop on input of a 'D'
jr $ra
I've checked my input as it comes in and even when in the array after saving. It seems my print is the problem, but I could easily be wrong. Any ideas?
The fix was rather easy. Instead of storing the user input into a separate memory location and then putting that location in my array, I simply had the user input be stored directly into my array. See code changes below.
.data
mem: .space 256 #256 bytes of space for input
.text
la $s1, mem #s1 used to take input
jal readLoop #Read input loop
la $a0, mem #Attempt to read very first saved input
li $v0, 4
syscall
li $v0, 10 #End program
syscall
readLoop:
li $v0, 8 #read string
la $a0, mem #set user input as memory location
addi $a1, $zero, 5 #length of buffer
syscall
lb $t2,($a0) #used to exit loop
addi $s1, $s1, 4 #increment memory by 4 bytes
li $t1, 'D'
bne $t2, $t1, readLoop #exit loop on input of a 'D'
jr $ra
I've just started to learn MIPS, and as part of our assignment, I'm trying to save a counter value that runs inside a loop.
So, I was able to exit the loop, thanks to Michael. But now the counter will not increase, I noticed that it won't enter the incount label.
.text
.globl main
main:
# get string from user
la $a0, str1 # load the addr of the given string into $a0.
li $v0, 4 # 4 is the print_string syscall.
syscall # do the syscall.
li $v0, 8 # take in input
la $a0, buffer # load byte space into addr
li $a1, 10 # allot the byte space for the string
move $t0, $a0 # save the string into $to
syscall
# get char from user
la $a0, char1 # load the addr of the given char into $a0.
li $v0, 4 # 4 is the print_string syscall.
syscall # do the syscall.
li $v0, 8 # take in input
la $a0, buffer # load byte space into addr
li $a1, 10 # allot the byte space for the char
move $t1, $a0 # save the char into $t1
syscall
addi $s2, $zero,0 # s2 holds the counter
loop:
lb $t3, ($t0)
beq $t3, $t1, incount # go to incount if char was found
beqz $t3, exit # go to exit if we arrived to the end of the string
addi $t0, $t0, 1 # incrase t3 by 1
j loop # go to loop
incount:
addi $s2, $s2, 1 # increase the counter by 1
addi $t0, $t0, 1 # incrase char pos by 1
j loop # go back to loop
exit:
la $a0, ($s2) # counter to be printed
li $v0, 1 # 1 is the print_int syscall.
syscall
li $v0, 10 # return control to SPIM OS
syscall
.data
buffer: .space 10
str1: .asciiz "Please enter your string: "
char1: .asciiz "Now, please enter your char of choice: "
# end countchar.s
Thanks in advance
You've placed your exit routine in the .data section, which is why you're getting the "invalid program counter value" error message. All code needs to be in the .text section.
.data
spaceChar: .asciiz " "
#array of 26 elements 1,0,0,0,0 elements = 5*5
array: .word 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,9
size: .word 25
endl: .asciiz "\n"
.text
main:
lw $t3, size
la $t1, array # get array address
li $t2, 0 # set loop counter
print_loop:
beq $t2, $t3, print_loop_end # check for array end
li $t5,4 #at 4th element I want next line
beq $t5,$t2,newline #checking..
lw $a0, ($t1) # print value at the array pointer
li $v0, 1
syscall
la $a0, spaceChar # Display a space character between elements
li $v0, 4
syscall
addi $t2, $t2, 1 # advance loop counter
addi $t1, $t1, 4 # advance array pointer
j print_loop # repeat the loop
print_loop_end:
li $v0,10
syscall
newline:
la $a0,endl
li $v0,4
syscall
j print_loop
Im trying to print a 5*5 matrix in MIPS This is a 1 dimensional array in mips of 25 elements, Im traversing through the elements in print_loop and when it hits the 4th element I want to do next line but when I run this (MARS 4.5) is freezing I dont know what Im doing please help
Short answer:
You're infinitely looping on newline.
Long answer:
The problem is
beq $t5, $t2, newline #checking
Once your counter gets 4, it keeps going to newline
newline:
la $a0, endl
li $v0, 4
syscall
j print_loop
Then it goes back to print_loop
print_loop:
beq $t2, $t3, print_loop_end #check for array end
li $t5, 4 #at 4th element I want next line
beq $t5, $t2, newline #checking
Uh-oh. We're back to our beq again! If you use the step-by-step debugger (the green arrow with a 1 next to the green arrow that runs), you'll see that you print the first row and then infinitely print newlines. Looks to me like you could just add another label in there after that beq.
In the future, I'd suggest commenting every single line and dividing code into chunks that complete objectives. For example:
# print value at the array pointer
lw $a0, ($t1) # print array[index]
li $v0, 1 # syscall: print integer
syscall
# print space
la $a0, spaceChar # print character " "
li $v0, 4 # syscall: print string
syscall
It's tedious, but it'll helps you sniff out bugs when everything is written in pseudocode. (plus, when someone asks a MIPS question on stackoverflow that you want to answer in a couple years, it helps you remember what the commands do! :P)
Oh, and you can just do
beq $t2, 4, newline
instead of
li $t5, 4
beq $t5, $t2
MIPS can be tricky. Just take it slow and document EVERYTHING. Good luck!
I can understand and use Java/c++ to a good extent, but for the life of me assembly just confuses me there are 2 functions I'm having trouble with. First:
One function that receives a string and prints it on the terminal
And another one that receives a string and converts it to integers (Strings given all made of numbers).
Any idea on where to start?
Update
On the second function, so far I got this:
main:
atoi:
li $v0, 8
la $a0, tstr
li $a1, 64
syscall
sub $sp, $sp,4
sw $ra, 0($sp)
move $t0, $a0
li $v0, 0
next:
lb $t1, ($t0)
beqz $t1, endloop
mul $v0, $v0, 10
add $v0, $v0, $t1
sub $v0, $v0, 48
add $t0, $t0, 1
b next
endloop:
lw $ra, 0($sp)
add $sp, $sp, 4
Updated code, still getting the error on 10 being an invalid operand. And about sub $v0, $v0, 48 should I just do it as sub $t1, $t1, 48?
For input-output stuff, you have to use system calls. For writing (zero-terminated) strings you'll use syscall #4, which wants the address of the buffer in $a0. Now just place the umber of the syscall in $v0 and execute it. For example, this snippet reads a string:
li $v0, 8 # syscall number
la $a0, theString # buffer
li $a1, 64 # length of buffer
syscall # read!
Here you can find some syscalls numbers.
For the second exercise, here's the C++ code, try to translate it :P
int result = 0;
while (*digit >= '0' && *digit <='9') { // digit is char *
result = (result * 10) + (*digit - '0');
digit++;
}
EDIT:
Ok, there are a couple of errors. First, you're not checking whether you've reached the end of the string (simply compare $t1 with 0 at the beginning). And you should first subtract '0' from $t1, then add it to $v0.
next:
lb $t1, ($t0)
# are there other character or this is the last one?
mul $v0, $v0, 10
add $v0, $v0, $t1
sub $v0, $v0, 48 # subtract 48 only from $t1, not from whole result
add $t0, $t0, 1
b next