New file. Basically m68k version with Hitachi SH comments thrown in.

doc/supplements/sh/callconv.texi

@@ -0,0 +1,102 @@
+@c
+@c  COPYRIGHT (c) 1988-1998.
+@c  On-Line Applications Research Corporation (OAR).
+@c  All rights reserved.
+@c
+@c  $Id$
+@c
+
+@chapter Calling Conventions
+
+@section Introduction
+
+Each high-level language compiler generates
+subroutine entry and exit code based upon a set of rules known
+as the compiler's calling convention.   These rules address the
+following issues:
+
+@itemize @bullet
+@item register preservation and usage
+@item parameter passing
+@item call and return mechanism
+@end itemize
+
+A compiler's calling convention is of importance when
+interfacing to subroutines written in another language either
+assembly or high-level.  Even when the high-level language and
+target processor are the same, different compilers may use
+different calling conventions.  As a result, calling conventions
+are both processor and compiler dependent.
+
+The Hitachi SH architecture supports a simple yet
+effective call and return mechanism.  A subroutine is invoked
+via the branch to subroutine (XXX) or the jump to subroutine
+(XXX) instructions.  These instructions push the return address
+on the current stack.  The return from subroutine (rts)
+instruction pops the return address off the current stack and
+transfers control to that instruction.  It is is important to
+note that the MC68xxx call and return mechanism does not
+automatically save or restore any registers.  It is the
+responsibility of the high-level language compiler to define the
+register preservation and usage convention.
+
+@section Calling Mechanism
+
+All RTEMS directives are invoked using either a bsr
+or jsr instruction and return to the user application via the
+rts instruction.
+
+@section Register Usage
+
+As discussed above, the bsr and jsr instructions do
+not automatically save any registers.  RTEMS uses the registers
+D0, D1, A0, and A1 as scratch registers.  These registers are
+not preserved by RTEMS directives therefore, the contents of
+these registers should not be assumed upon return from any RTEMS
+directive.
+
+
+> > The SH1 has 16 general registers (r0..r15)
+> > r0..r3 used as general volatile registers
+> > r4..r7 used to pass up to 4 arguments to functions, arguments above 4 are
+> > passed via the stack)
+> > r8..13 caller saved registers (i.e. push them to the stack if you need them
+> > inside of a function)
+> > r14 frame pointer
+> > r15 stack pointer
+>
+
+
+@section Parameter Passing
+
+RTEMS assumes that arguments are placed on the
+current stack before the directive is invoked via the bsr or jsr
+instruction.  The first argument is assumed to be closest to the
+return address on the stack.  This means that the first argument
+of the C calling sequence is pushed last.  The following
+pseudo-code illustrates the typical sequence used to call a
+RTEMS directive with three (3) arguments:
+
+@example
+@group
+push third argument
+push second argument
+push first argument
+invoke directive
+remove arguments from the stack
+@end group
+@end example
+
+The arguments to RTEMS are typically pushed onto the
+stack using a move instruction with a pre-decremented stack
+pointer as the destination.  These arguments must be removed
+from the stack after control is returned to the caller.  This
+removal is typically accomplished by adding the size of the
+argument list in bytes to the current stack pointer.
+
+@section User-Provided Routines
+
+All user-provided routines invoked by RTEMS, such as
+user extensions, device drivers, and MPCI routines, must also
+adhere to these calling conventions.
+