SPIM provides a small set of operating system-like services through the system call (syscall) instruction. To request a service, a program loads the system call code (see table below) into register $v0 and arguments into registers $a0...$a3 (or $f12 for floating-point values). System calls that return values put their results in register $v0 (or $f0 for floating-point results).

Service Name

System call code

Arguments

Results

Print Integer

1

$a0 = integer

 

 

Print Float

2

$f12 = float

 

 

Print Double

3

$f12 = double

 

 

Print String

4

$a0 = string

 

 

Read Integer

5

 

 

Integer value in $v0

Read Float

6

 

 

Floating-Point value in $f0

Read Double

7

 

 

Double in $f0

Read String

8

$a0 = Buffer, $a1 = length

 

 

sbrk

9

$a0 = amount

Address in $v0

exit

10

 

  		 


Sbrk returns a pointer to a block of memory containing n additional bytes. Exit stops a program from running.