File content as of revision 1:6d520aa1463b:

#include <mbed.h>
#include <DigitalIn.h>
#include <Pulsator.h>
#include <USBKeyboard.h>

// ACTIVE LOW
#define PI_BUTTON P0_7
#define PO_LED P1_15

#define BUTT_KEY '1'
#define BUTT_DN KEY_CTRL | KEY_ALT
#define BUTT_UP KEY_CTRL | KEY_ALT | KEY_SHIFT

#define PERIOD_DN 0.25f
#define PERIOD_UP 2.0f

DigitalIn butt(PI_BUTTON, PullUp);
USBKeyboard kbd;
Pulsator led(PO_LED);

static float flashing(float x)
    { return x < 0.125f || x >= 0.25f && x < 0.375f ? 1.0f : 0.0f; }

#define BRIEFLY 0.125f
int main(void)
{
    led.active_high(false).fun(&flashing).period(PERIOD_UP) = true;
    while(!kbd.configured()) wait(BRIEFLY);
    led.fun(NULL);

    for(bool now = butt; ; wait(BRIEFLY))
    {
        if(now == butt) continue;
        now = !now;
        kbd.keyCode(BUTT_KEY, now ? BUTT_UP : BUTT_DN);
        led.period(now ? PERIOD_UP : PERIOD_DN);
    }
}