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diff --git a/doc/supplements/m68k/callconv.t b/doc/supplements/m68k/callconv.t deleted file mode 100644 index e572fb4e64..0000000000 --- a/doc/supplements/m68k/callconv.t +++ /dev/null @@ -1,92 +0,0 @@ -@c -@c COPYRIGHT (c) 1988-2002. -@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. - -@section Processor Background - -The MC68xxx architecture supports a simple yet -effective call and return mechanism. A subroutine is invoked -via the branch to subroutine (bsr) or the jump to subroutine -(jsr) 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. - -@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. - |