Re: How to configure GNAT GPL on x86-64 Linux for ARM ELF development

[Adam Jensen <hanzer@riseup.net>]

On Thu, 24 May 2018 12:12:26 +0000, Brian Drummond wrote:

> The error you saw "Cannot find system.ads" and Simon's answer arise
> because, targeting small embedded CPUs, you are looking below the full
> Ada environment (supplied by the runtime system (RTS) on the host
> machine, to targets which may require unique runtimes supplying the
> facilities you need and nothing more (thanks to potential space
> limitations).
> 
> As such I would suggest a ZFP RTS as a good short-term study,for several
> reasons:
> 
> it can be a pretty small codebase, but revealing in terms of how things
> are done and how to adapt them.
> 
> there are a plethora of targets out there, un- or semi-supported by Ada,
> from the AVR and MSP430 to ARM cores from ST, NXP, TI and others.
> Starting with the STM4 as you are is good, but you may want to port to
> other platforms for cost, power, security or other reasons ... the TI
> Hercules which runs dual ARM cores in lockstep for safety, has obvious
> attractions as an Ada target, for example.
> 
> Nice price too ... https://store.ti.com/LAUNCHXL-TMS57004.aspx
> 

Adacore's Gnat GPL seems to include a full Ravenscar RTS for Xilinx's 
zynq7000 ARM/FPGA SoC:

<https://www.xilinx.com/products/boards-and-kits/device-family/nav-
zynq-7000.html>

One of those development kits might be my next target platform, but 
successfully configuring tools from two different vendors for hardware/
software co-design - simulation, emulation, and cross-compilation - on a 
third-party OS (Ubuntu or RHEL) seems like a long way off. Right now, 
configuring a Ravenscar/Spark development environment that can produce a 
binary for the Nucleo-144 board that will flash an LED is the 
[surprisingly challenging] goal :)  

> And porting to these builds on understanding the RTS, starting with the
> simplest - ZFP - as in Simon's suggestion - or AVR-Ada or my MSP430-Ada
> adaptation. I finally got round to machining the case and bezel, so I am
> wearing a wristwatch running Ada, telling the time 1970's style, in
> under 1 kilobyte including RTS.
> 
> (the current version still has 200 bytes of C startup code which the
> linker insists on inserting by default; one TODO is to persuade the
> linker to let me replace that with pure Ada and strip out the
> unnecessary stuff)
> 

That seems [to me] like a curiously superfluous application of the 
technology but rock on, dude.
 
> 
> You suggest going in 2 more interesting directions:
> 
> building up to a Ravenscar profile : I believe Simon's work so far
> builds on FreeRTOS, but a "native" Ravenscar RTOS would be nice too...
> 
> SPARK qualification would be excellent ... again, especially for the
> Hercules. And again, a SPARK proven ZFP RTS would be a good base to
> build on, and a relatively simple place to start.

Is it common for developers to create their own run-time system for 
embedded platforms? My inclination would be to look for hardware based on 
1) RTS availability/quality and 2) toolkit complexity/completeness 
(completeness implies useful documentation). Given that, which seems like 
an obvious thing to do, I am surprised that Adacore does not have more 
apparent associations with hardware vendors where dev-kits and SBC 
products are promoted. I bought the Nucleo-144 board because I thought 
there was a BSP, RTS, and a tool-chain configuration tutorial. That 
turned out to be a bit of a mistake and generally a poor choice. If 
Adacore, or some other enterprising entrepreneur, offered well-developed 
BSP, RTS, tool-chain configuration and programming tutorials for several 
MCU dev-kits and SBC (single board computer) products, that would make 
the choice easy and actually enable people to get started with the 
technology in a reasonable way. It seems so bizarre to me that this isn't 
a front-page item for Adacore. I guess there are hidden obstacles in 
their business model and the way the incentives are arranged in their 
social organization. I suppose it could have something to do with 
European culture. In France, does pedagogy have the demeanor of a wood-
chipper (e.g., is it based in punishment, toil, and obscurity)? <smirk>