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The system call instruction supports special, ``OS-like'' calls that provide useful services to assembly language programs. These calls work by putting a ``system call ID'' value into register $1 and the argument to the call in register $2 and then executing the syscall instruction. The result of the instruction (if any) is placed into register $1. While it may take multiple instructions to fill the registers for the system call, actually executing the system call is an atomic operation.
The DCoreWars engine MUST support the following system calls:
| Syscall ID ($1) | Argument ($2) | Description
|
|---|---|---|
| 0 | none | HALT -- equivalent to the hlt instruction |
| 1 | none | Random -- return a random, unsigned integer in the range
![$ [0\dotsb 2^{32}-1]$](img17.png){kind=small} . |
| 2 | none | Memsize -- return the memory size of the RVM on which the instruction is executed |
| 3 | none | Netsize -- return the number of hosts on the current network |
| 4 | none | GetPID -- return a unique identifier for the currently executing PROCESS |
| 5 | none | GetPGID -- return a unique identifier for the currently executing PROCESS GROUP |
| 6 | none | GetNPG -- return the number of RUNNABLE PROCESS GROUPs on the current RVM |
| 7 | none | GetNPlayers -- return the number of players in the current game |
| 8 | PGID | Score(PGID) -- return the current score (number of memory cells owned by) the specified PROCESS GROUP |
| 9 | RPGID | RemoteProc(RPGID) -- return 1 if the specified PROCESS GROUP is RUNNABLE on the remote host currently connected to the SOCKET of the executing PROCESS, or 0 otherwise. Invoking this system call when the current SOCKET is empty (not yet connected or connection terminated) returns 0. |
| 10 | RPGID | RemoteScore(RPGID) -- return the score (number of memory cells owned by) the specified PROCESS GROUP on the remote host currently connected to the SOCKET of the executing PROCESS. Invoking this system call when the current SOCKET is empty (not yet connected or connection terminated) returns 0. |
| 11 | PGID | GetNProcs(PGID) -- return the number of RUNNABLE PROCESSes in the specified PROCESS GROUP. |
The implementors are free to provide additional system calls, at their option, but all such system calls MUST be fully documented. Invoking an undocumented system call is an ILLEGAL OPERATION for the invoking process.