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Section A.2 OS Calls

Calling the operating system is done by the syscall instruction. The operation to be carried out is specified by the $v0 register. Potential arguments to the system call are passed in the argument registers.

Action $v0 Description
print integer 1 $a0 = number to be printed.
print string 4 $a0 = address of ASCIIZ string.
read integer 5 Read number stored in $v0.
read string 8

$a0 = start address of memory area where characters are put. $a1 = maximum number of characters to read.

exit 10 End program execution.
print character 11 $a0 = ASCII code of character to print.
read character 12 ASCII code of read character stored in $v0.