These are baremetal examples for the BBC micro:bit board.

http://microbit.org/

There are two microcontrollers one is basically the debug header
it is what the usb plugs into, we dont program it we use it to
get at the other microcontroller which we do program:

Nordic nRF51822

According to wikipedia

16 MHz 32-bit ARM Cortex-M0 microcontroller
256 KB flash memory
16 KB static ram
2.4 GHz Bluetooth low energy wireless networking

The debug mcu provides an MBED type interface meaning the board will
show up looking like a flash drive, you copy your binary to that
drive and it will download that binary into the Nordic MCU and reset.

So for example if you build blinker01 and copy notmain.bin to the
drive that mounts when you plug in the board, then as the README in
that directory describes one of the LEDs will start blinking.  It
is programmed into flash so unplugging and re-plugging will still
run that program.  (yes this overwrites the stock program that comes
with the board, that is kind of the point here to make your own
programs).

If you go to their github site

https://github.com/bbcmicrobit/

specifically

https://github.com/bbcmicrobit/hardware

You can download the schematic for the board.

Websites change but as of this writing if you go here

https://www.nordicsemi.com/

Then in the top right-ish click documentation it is very much like
the ARM infocenter site (hmmm) expand nRF51 Series on the left side
Then click on Reference Manual on the left side, then on the right
click on the most recent version of reference manual.  Pretty much
every other MCU site you go to the product page for that MCU and
they have these kinds of documents there.  Also this document doesnt
have a whole lot of pages which usually the manual with the register
spec has hundreds of pages.  This has the register specs.

The debug interface also provides a virtual uart ACM0, which the
examples will use.

It appears that we do not have a systick timer in this core, sigh.