This interface defines platform (machine + OS) dependent types and constants.

INTERFACE RTMachine;

IMPORT Csetjmp;
FROM Upthread IMPORT pthread_t;
IMPORT Word;

TYPE
  State = Csetjmp.jmp_buf;
  (* The machine state is saved in a "State". This is opaque to the client. *)

<*EXTERNAL "_setjmp" *>
PROCEDURE SaveState (VAR s: State): INTEGER;

Capture the currently running thread's state

CONST
  FramePadBottom = 0;
  FramePadTop    = 0;
  StackFrameAlignment = 0;

The heap page size used to be machine-dependent, since it could depend on the architecture's VM page size (if VM was TRUE). VM is now always FALSE. Otherwise, 8192 bytes is a reasonable page size. The page size must be a power of two.

BytesPerHeapPage    = Word.LeftShift(1, LogBytesPerHeapPage); (* bytes per page *)
  LogBytesPerHeapPage = 13;
  AdrPerHeapPage      = BytesPerHeapPage;   (* addresses per page *)
  LogAdrPerHeapPage   = LogBytesPerHeapPage;

PointerAlignment = BYTESIZE(INTEGER);
  (* The C compiler allocates all pointers on 'PointerAlignment'-byte
     boundaries. The garbage collector scans thread stacks, but only
     looks at these possible pointer locations. Setting this value
     smaller than is needed will only make your system run slower.
     Setting it too large will cause the collector to collect storage
     that is not free. *)

Has_stack_walker = FALSE;
  (* Indicates whether this platform supports the stack walking functions
     defined in the "RTStack" interface. *)

TYPE FrameInfo = RECORD pc, sp: ADDRESS END;

CONST
  SuspendThread: PROCEDURE(t: pthread_t): BOOLEAN = NIL;
  RestartThread: PROCEDURE(t: pthread_t) = NIL;
  GetState: PROCEDURE(t: pthread_t; VAR state: ThreadState): ADDRESS = NIL;
  SaveRegsInStack: PROCEDURE(): ADDRESS = NIL;

TYPE ThreadState = RECORD END;

END RTMachine.