It is a basic assembly instruction that corresponds to a 32-bit machine instruction.
| Service | Code in $v0 | Arguments | Returned Value |
|---|---|---|---|
| print integer | 1 | $a0 == integer | |
| print float | 2 | $f12 == float | |
| print double | 3 | ($f12, $f13) == double | |
| print string | 4 | $a0 == address of string | |
| read integer | 5 | $v0 == integer | |
| read float | 6 | $f0 == float | |
| read double | 7 | ($f0, $f1) == double | |
| read string | 8 | $a0 == buffer address$a1 == buffer length | |
| allocate memory | 9 | $a0 == number of bytes | $v0 == address |
| exit | 10 |
Here are the services of the SPIM exception handler. The following pages explain how to use them. The print services write characters to the simulated monitor of SPIM. The read services read characters from the keyboard and (for numeric read services) convert character strings into the appropriate type.
Load register $v0 with the code for the
service you wish to use and load other specific registers with
parameters for the service.
For example, The exit service gracefully stops the program. It takes no parameters, so all you need is the service code. Until now we have been single stepping the program or crashing into the bytes beyond the end of the program.
li $v0,10 # code 10 == exit
syscall # Return control to the
# operating system.
What do you think the exit service does for a program running on a computer with a real operating system?