From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00
	autolearn=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: ANN: Cortex GNAT RTS 2018-07-15
Date: Mon, 16 Jul 2018 12:56:45 +0100
Organization: A noiseless patient Spider
Message-ID: <lywotve6ma.fsf@pushface.org>
References: <ly1sc4ffrq.fsf@pushface.org> <87in5gf9nt.fsf@nightsong.com>
Mime-Version: 1.0
Content-Type: text/plain
Injection-Info: reader02.eternal-september.org;
 posting-host="3287f85329b59e6d5bcd46787983fc9a";
	logging-data="1987"; mail-complaints-to="abuse@eternal-september.org";
	posting-account="U2FsdGVkX18KvD8a7IeJmOk6oy6F+B++LXcpyMMdWwM="
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.3 (darwin)
Cancel-Lock: sha1:cGIWlmEEEa9zMHrVN/UQxD7eHgs=
	sha1:W5H2rVIFZFa2aGx604de63EVwIw=
Xref: reader02.eternal-september.org comp.lang.ada:53842
Date: 2018-07-16T12:56:45+01:00
List-Id: <comp.lang.ada>

Paul Rubin <no.email@nospam.invalid> writes:

> Can you say about how hard it is to port GNAT RTS to a new board,
> given a reasonable C environment for the board?  How much code space
> and ram is required?

I don't know about the AdaCore RTS, but I imagine it'll be much the same
as this one (after you've got to grips with the deeply nested,
use-clause-happy code :-)

For this one, I started on 1 July and had a working RTS (bar an issue
with the board clock, discovered later) by 4 July.

The issues (once you have a base RTS for one ARM board) are

* startup, any RAM/Flash/FPU settings, clock
* interrupts, interrupt priority range, names

For the micro:bit, compiling with -O0 and assertions enabled, I get, for
the RTS + other support, in a program with delays, a task, and an
interrupt-handling PO,

text
        libgcc      1380
        gnat       10132
        freertos    7724
        libc         280

rodata
        gnat        1252

data
        gnat         220
        freertos       4

bss
        gnat          68
        freertos     340

The base RAM use (data + bss) for this program was 900 bytes. Out of the
remaining RAM (15484), it used (via heap allocations)

initial/interrupt stack   1024
environment task stack    1536
1 task stack              1024
others?                    828

and the free heap was 11072 (those numbers don't quite add up, I think
there's some overhead in the heap management maybe).

I'm not sure why the environment task stack needs to be so high (it does
elaboration + Ada main). The task stack could probably be lower, one
outstanding job is to work out a way of measuring task stack usage.