Re: Passing Ada Proc as a C Function Pointer

[Warren <ve3wwg@gmail.com>]

On Aug 5, 3:33 am, Rolf <rolf.ebert_nosp...@gmx.net> wrote:
> On 5 Aug., 02:45, Warren <ve3...@gmail.com> wrote:
>
> > On Aug 4, 3:46 pm, Simon Wright <si...@pushface.org> wrote:
>
> > > I would be a bit worried about Thread_Proc's *Ada* environment. There's
> > > this thing called the Secondary Stack, used for - for example - string
> > > catenation; and it's not set up here.
>
> > Yikes, that could be a problem. I vaguely remember something about
> > a "secondary stack".  I'm going to need to research this.
>
> The current version of AVR-Ada does not support the secondary stack.
> It is required for returning unconstrained objects from functions.
> Using unconstrained arrays already consumes so much of the valuable
> RAM that I never felt the need to support returning these objects from
> functions.

Thanks Rolf!

If I hard code the call to the Ada proc from the start thread in the
C code, the threaded code works great now (in Ada!)  So I just got to
work out this business of the C function pointer.

The other issue I have is to sort out the declaration of the Context
object in Ada. If I declare the context in C, things go well.

Attempting to get the C_Context_Type declared correctly is proving
to be a challenge. Here is what I have:

--  typedef enum {
--      ats_normal,
--      ats_wait,
--      ats_clear = 0x40,
--      ats_tick = 0x80
--  } __attribute__((packed)) avr_thread_state;
--
--  typedef struct avr_thread_context {
--      volatile avr_thread_state state;
--      uint8_t* stack_ptr;
--      volatile struct avr_thread_context* next;
--      volatile int16_t timeout;
--      volatile void* waiting_for;
--      volatile struct avr_thread_context* next_waiting;
--      volatile struct avr_thread_context* prev_waiting;
--  } avr_thread_context;

    type C_Context_Type is
        record
            State :         Unsigned_16;
            Stack_Pointer : System.Address;
            Next :          System.Address;
            Timeout :       Unsigned_16;
            Waiting_For :   System.Address;
            Next_Waiting :  System.Address;
            Prev_Waiting :  System.Address;
        end record;

    pragma Convention(C,C_Context_Type);
    pragma Pack(C_Context_Type);
    for C_Context_Type'Size use 16;

Keep in mind I am NOT interested in using the members of
C_Context_Type, but simply trying to set aside storage
that would match the C declaration (in bytes). I've
also tried declaring arrays, but I get a similar
experience (dope vectors etc. balloon the space).

When I compile the above, I get the complaint:

avr_threads.ads:58:33: size for "C_Context_Type" too small, minimum
allowed is 112

112 bytes - yikers!  How do I get this right?

Warren