Feature/interruptable calibration

[m-mcgowan]

Interrupts the calibration screen after 60s.

This PR includes:

• support for FreeRTOS via the freertos4core lib, included as a subtree
• D4D screen calibration cancellable asynchronously
• use of FreeRTOS timer to cancel the touch screen calibration
• DS248x fix to not call init() in the constructor which can cause a SOS

[m-mcgowan]

Testing:

• pull the latest develop branch from the particle firmware
• build this branch
• flash to the device
• force calibration (how do we do this? we used to have the 'T' command.) Erase eeprom sectors with jtag?
• verify that the screen times out after 10 seconds.

[elcojacobs]

I just tried building/flashing feature/interruptable_calibration on the photon. make all program-dfu PLATFORM=photon in spark-firmware/modules on branch latest make all program-dfu PLATFORM=photon SPARK_CLOUD=n USE_PRINTF_FLOAT=n in firmware/platform/spark

An SOS occurs when entering touch screen calibration, by pressing the screen during the logo. If I don't trigger it by tapping the screen during the logo and skip touch screen calibration, I don't get the SOS.

[m-mcgowan]

Be sure to flash the latest system firmware:

cd platform/spark
pushd firmware/modules
make PLATFORM=photon all program-dfu
popd

make PLATFORM=photon all program-dfu

For SWD support, add USE_SWD=y to the system modules build. (and be sure to do a clean build.)

[elcojacobs]

now flashed system modules from subdir, instead of from spark repo. No SOS this time. I think my spark firmware repo was newer than the local subtree, which was used in the build. 3 things:

• Timeout seems to be about 2 seconds, instead of 10
• Please add instructions to update the subtrees to the readme
• Instructions above should read PLATFORM=photon instead of PLATFORM_ID