The micro:bit is a small embedded system equipped with a Nordic Semiconductor nRF51822 controller based on the Cortex-M0 architecture. With FPC trunk, it is possible to build programs for it. Follow the instructions at  to setup FPC for the target arm-embedded. However, do not use the provided command line to build and install FPC but use
make clean buildbase installbase CROSSINSTALL=1 OS_TARGET=embedded CPU_TARGET=arm SUBARCH=armv6m
instead to build FPC for the controller used by the micro:bit.
Now enter the following program:
const GPIO_PIN_CNF_INPUT_Disconnect = 1; GPIO_PIN_CNF_DIR_Output = 1; microbit_led_col1 = 4; microbit_led_row1 = 13; var i : longint; begin GPIO.PIN_CNF[microbit_led_col1]:=(GPIO_PIN_CNF_INPUT_Disconnect shl 1) or GPIO_PIN_CNF_DIR_Output; GPIO.PIN_CNF[microbit_led_row1]:=(GPIO_PIN_CNF_INPUT_Disconnect shl 1) or GPIO_PIN_CNF_DIR_Output; while true do begin GPIO.OUTSET:=1 shl microbit_led_row1; GPIO.OUTCLR:=1 shl microbit_led_col1; for i:=1 to 500000 do asm nop end; GPIO.OUTCLR:=1 shl microbit_led_row1; for i:=1 to 500000 do asm nop end; end; end.
save it as example.pp and compile it with:
fpc -Parm -Tembedded -Wpnrf51822_xxaa example -Cparmv6m
When connecting a micro:bit to PC, it identifies itself as an USB drive. Find out where this drive is located and copy the resulting example.hex to this drive.
If everything worked fine, the upper left LED will blink.