__WFI is not standardized, though often provided. As it's not a core part of this example, drop it.
README
This example demonstrates the use of timers to trigger an interrupt. This example will toggle a LED spelling out the following morse code:
SOS -> ...---...
using international morse timing, with a dot element of 100ms
It's intended for the ST STM32F4DISCOVERY eval board. It should blink a LED on the board.
Board connections
none required