Notes and examples referring to the study of the set of instructions that form the basis of low-level programming of processors with a focus on the set of instructions of the 32-bit MIPS architecture.
MIPS programs can make system calls by placing parameters in specified registers, depending on the call, and executing a trap instruction. Returned results are made available in other specified registers, also depending on the call.
The trap mechanism used differs from the syscall mechanism used by real MIPS. However, the numbers used to identify the system calls are the same. (where possible)
| Service | Trap Code | Input | Output | Notes |
|---|---|---|---|---|
| print_int | 1 | $4 is int to print | Print an int value to standard output in decimal. | |
| print_float | 2 | $f12 is float to print | NOT IMPLEMENTED! Print a float value to standard output. | |
| print_double | 3 | $f12 (with $f13) is double to print | NOT IMPLEMENTED! Print a double value to standard output. | |
| print_string | 4 | $4 is address of ASCIIZ string to print |
Print an ASCIIZ string to standard output. The contents of $1 are destroyed in the process. |
|
| read_int | 5 | $2 is int read | Read a line of standard input as an int value expressed in decimal. | |
| read_float | 6 | $f12 is float read | NOT IMPLEMENTED! Read a line of standard input as a float value. | |
| read_double | 7 | $f12 (with $f13) is double read | NOT IMPLEMENTED! Read a line of standard input as a double value. | |
| read_string | 8 | $4 is address of buffer, $5 is buffer size in bytes | Read a line of standard input into a string buffer. The contents of $1 are destroyed in the process. | |
| sbrk | 9 | $4 is number of bytes required | $2 is address of allocated memory | NOT IMPLEMENTED! Allocate memory from the heap. |
| exit | 10 | Terminate execution of the MIPS program. | ||
| print_byte | 101 | $4 contains byte to print | Print a single byte to standard output. | |
| read_byte | 102 | $2 contains byte read | Read a single byte from standard input. | |
| set_print_inst_on | 103 | For debugging. Turns on printing of each instruction before execution. | ||
| set_print_inst_off | 104 | For debugging. Turns off printing of each instruction before execution. | ||
| get_print_inst | 105 | $2 contains current status of printing instructions |