Re: gnat ARM - predefined packages

[Simon Wright <simon@pushface.org>]

"RasikaSrinivasan@gmail.com" <RasikaSrinivasan@gmail.com> writes:

> Some clarifications please:
>
> I am using gnat for ARM - having reasonable success with the STM32F4
> discovery board.

There's the RTS that AdaCore provide with their cross compiler, which
includes packages like STM32F4.GPIO, and the RTS that I've been working
on. I think you're using the former.

> I would like to know:
>
> - The example project contains an import as follows:
>
> -- file: registers.ads
>     GPIOD : GPIO_Register with ... ;
>     pragma Import(Ada,GPIOD) ;
>
>     where is this object GPIOD getting imported from?

The actual code is

   GPIOD : GPIO_Register with
     Volatile,
     Address => System'To_Address (GPIOD_Base);
   pragma Import (Ada, GPIOD);

(GPIO_Register comes from package STM32F4.GPIO: I'm surprised that
AdaCore use 'use' like this, it's quite unnecessary here).

The point of the pragma Import is to prevent any initialization that the
compiler might do on the object. I don't think that there is any in this
case, but consider an access variable: the default initialization is to
set it to null, which you certainly don't want to do to a hardware
register unless you ask for it.

>     I am looking to use GPIOB and GPIOC. how can i import those?

exactly as GPIOD; the corresponding _Base declarations are in package
STM32F4.

> - the spec of Ada.Interrupts.Names so I know how to attach new
> interrupt handlers. (Example project provides
> Ada.Interrupts.Names.EXTIO_Interrrupt)

This is a-intnam.ads in your RTS's adainclude/ directory.

If you're looking at AdaCore's RTS, there's an _extremely_ misleading
comment about Interrupt_ID 0 being reserved (well, I was misled; it
probably doesn't matter to you).

> - Is it possible to install native gnat on the same Windows system and
> produce executables for both the native and the ARM targets?

I can't speak for GNAT GPL on Windows, but it would be completely normal
to have the native compiler installed first, then install the
cross-compiler on top of it (THEY MUST BE THE SAME VERSION). In fact
don't you need to? does the cross compiler include all the tools,
e.g. gprbuild, GPS?

> - Is it possible to use packages such as Ada.Containers in the
> embedded target?

Probably not; the AdaCore RTS doesn't support controlled types, my RTS
doesn't (yet) include controlled types or allocators or streams, nor
does it allow dispatching (so no classwide types).