Setting default_library to 'small' in mbed_app.json

Mbed OS
1

I can create a custom target and change the library setting to ‘small’ to use newlib nano. I know it is only safe when the RTOS is not used, but this already possible with the bare-metal option. In this case, the newlib nano will also save about 30 kB of flash size.
I think it makes more sense to set this option per app in mbed_app.json, but with the existing options it did not work. Is there a way to change this setting in mbed_app.json?

2

Hi Johannes,

I use below configuration in mbed_app.json

{
    "requires": ["bare-metal"],
    "target_overrides": {
        "*": {
            "target.default_lib": "small"
        }
    }
}

And build mbed-os-example-blinky-baremetal on K64F, it saves about 24KBs, could you elaborate what doesn’t work in your environment?

Regards,
Desmond

3

Thanks Desmond,
your solution is working. I had tried “default_lib”: “small”, that was not accepted. But with target.default_lib it does.

4

Is this similar to my question here?

https://forums.mbed.com/t/re-how-to-change-compiler-from-arm-std-to-arm-micro-toolchains/6344

I tried the “target.default_lib”: “small” on a couple of targets but did not see any size change on the Flash output file?
Also would this work when using the online compiler?

5

I’m not sure if this setting should work with Keil, it looks like the settings are different for the toolchains. For gcc-arm, it works and with ‘small’ the newlib nano is used. For the ARM compiler, the uARM toolchain is selected and also using the leaner library.
There is a Youtube video with some interesting information:

As far as I understand, this setting will be refurbished und unified.

see also:
https://github.com/notifications/beta/MDE4Ok5vdGlmaWNhdGlvblRocmVhZDY1NjMwODU4Mzo2Nzc1NTYy?query=repo%3AARMmbed%2Fmbed-os