Re: Ada and Automotive Industry

[frank@bigdog.engr.arizona.edu (Frank Manning)]

In article <1996Nov12.192850.16867@ole.cdac.com> james@cdac.com
(James Thiele) writes:

> Frank Manning writes:
>
>> It's a myth that Ada compilers are unrealistic for small
>> microcontrollers. There's nothing that prevents anybody from
>> implementing an Ada subset that could both (a) be validated and
>> (b) fit harmoniously on a small machine.
>>
>>[...]
>
> An 8051 and other 8-bit processors are small even for C.  I know
> of only one target of gcc to a machine of this class, 68HC11.  This
> port has no floats or 4 byte longs.

Don't forget it's possible to do useful work on the little guys even
with an interpreted BASIC (I have), which includes full floating
point. Otherwise nobody would make any money selling SBC's with
built-in BASIC interpreters. It's difficult to find a less efficient
language than that.

> If you look at 8051 C compilers you will find that they have evolved
> over the years adding little "hints" to deal with quirks in the
> address space.  The 8051 is a classic Harvard machine with different
> code and data spaces.  In addition, and here is one of the problems,
> it handles on and off chip RAM differently.
>
> Since it has only one accumulator and one data pointer there is
> likely going to be code bloat just trying to move data around.
> If you read postings in the relevant newsgroups you will see
> postings about features of C to avoid on the 8051 because they
> are expensive.

Well, that's true of any machine and any language. For example, if
your target is an x86SX and the language is C, floating point is
hugely more expensive than integer arithmetic. If the application
requires you to squeeze as much performance as possible out of a
machine, there's no substitute for intimate knowledge of the hardware
quirks in any case.

> Originally C was designed around PDP-11 class machines: 16 bits,
> multiple registers, indirect addressing modes, etc.  Since gcc has
> to dumb down C for an 8-bit machine, how much would GNAT have
> to dumb down Ada to target an 8051?  Would you still think it was Ada?

The important thing is from an economic point of view -- whether the
subset still encourages good software engineering practices, and how
easy it would be to retrain Ada programmers to use the subset
effectively, compared to programmers in alternative languages.

-- Frank Manning