Platform support for mbed-util

[bogdanm]

The initial aim for this library was to be independent from mbed-core and mbed in general, but that has a number of issues:

• mbed-util needs a runtime error function. The mbed implementation of the runtime error function (https://github.com/ARMmbed/mbed-sdk-private/blob/master/source/error.c) depends on the target support for STDIO messages.
• mbed-util needs an assert function. The mbed implementation of the assert function (https://github.com/ARMmbed/mbed-sdk-private/blob/master/source/assert.c) calls 'mbed_die', which is mbed specific.

To address this, there's now a 'mbed-util.h' header that contains the necessary functions and an implementation that gets included only for mbed targets (in mbed-util_mbed.c). Other implementations (for example POSIX) can be added on top of this. Eventually I expect 'mbed-util_mbed.c' (and other similar files that'll likely be added) to be spawned into a separate repository.

With this pattern, it's still possible to use this library in a POSIX environment (for example) with relative ease (implement mbed-util for POSIX and add a target POSIX dependency).

If this gets in, the corresponding functions in mbed-core should be expressed in terms of functions in mbed-util, to avoid code duplication.

[bogdanm]

@0xc0170 , @autopulated , this is needed for the proper implementation of the Array class (and for further improvements to the code, especially adding various ASSERTs)

[autopulated]

looks good – maybe provide a minimal implementation for non-mbed targets (even if it just while(1);s )?

[bogdanm]

I bet @rgrover would want to take care of that :)

[rgrover]

I'll port and test mbed-util to POSIX

[0xc0170]

+1