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From: Warren <ve3wwg@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Passing Ada Proc as a C Function Pointer
Date: Thu, 5 Aug 2010 09:51:43 -0700 (PDT)
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Date: 2010-08-05T09:51:43-07:00
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On Aug 5, 11:37=A0am, Warren <ve3...@gmail.com> wrote:
> Arg!!!! =A0Arg!!!!
>
> I keep thinking in terms of bytes - not BITS!! =A0No wonder!
>
> Warren

At long last-- it works!!!!

I ended up creating a C routine for the launch:

void
avr_thread_start_ada(
  avr_thread_context* context,
  uint8_t* stack,
  uint16_t stack_size) {
        extern void thread_thunk(void);  /* Ada in C convention */

        avr_thread_start(context,thread_thunk,stack,stack_size);
}

which is called by Start_Thread in Ada. This then invokes the usual
avr_thread_start(), which then launches the Ada (in C convention)
routine Thread_Thunk:

    procedure Thread_Thunk;
    pragma export(C,Thread_Thunk,"thread_thunk");

    procedure Thread_Thunk is
        Context : Thread_Context_Ptr :=3D Get_Context;
    begin
        Context.Ada_Proc.all;  -- Start Ada code in new thread
    end Thread_Thunk;

There was an undocumented AVR_Threads routine in the include file
that allowed me to pick up the active context, which is used by
Ada routine binding Get_Context.

The context object turned out to be tricky because the C context
object needed to be "struct aligned", which appears to be 64-bit.
So a little work on that fixed it. I also rolled the stack into
the object as a variant record, for user convenience:

    type Thread_Context(Stack_Size : Unsigned_16) is
        record
            C_Context :     aliased C_Context_Type;
            Ada_Proc :      Thread_Proc;
            Stack :         aliased Stack_Type(1..Stack_Size);
        end record;

    for Thread_Context use
        record
            C_Context       at  0 range 0 .. 16 * 8 -1;     -- Must be
first to be 64-bit aligned
            Stack_Size      at 16 range 0 .. 15;            -- Moved
here - non critical
            Ada_Proc        at 18 range 0 .. 15;            -- Non
critical placement
        --  Stack           at 20 range 0 .. Stack_Size * 8 - 1;
        end record;

Thanks to everyone for their comments and ideas.

Warren