setWatch(function()

Well now I success. I found the error in:
Espruino-master/targets/stm32/jshardware.c, downloaded today.
It say's espruino_1v72_stm32f3discovery.bin when compiled.

I have changed the following lines:

static ALWAYS_INLINE uint8_t pinToEVEXTI(Pin ipin) {
  JsvPinInfoPin pin = pinInfo[ipin].pin;
  return (uint8_t)(EV_EXTI0+pin); // PB
//  return (uint8_t)(EV_EXTI0+(pin-JSH_PIN0));

static ALWAYS_INLINE uint16_t stmPin(Pin ipin) {
  JsvPinInfoPin pin = pinInfo[ipin].pin;
  return (uint16_t)(1 << pin); // PB
//  return (uint16_t)(1 << (pin-JSH_PIN0));

static ALWAYS_INLINE uint32_t stmExtI(Pin ipin) {
  JsvPinInfoPin pin = pinInfo[ipin].pin;
  return (uint32_t)(pin); // PB
//  return (uint32_t)(1 << (pin-JSH_PIN0));

static ALWAYS_INLINE uint8_t stmPinSource(JsvPinInfoPin ipin) {
  JsvPinInfoPin pin = pinInfo[ipin].pin;
  return (uint8_t)(pin); // PB
//  return (uint8_t)(pin-JSH_PIN0);

The fault is in section 3: it vent 1,2,4 and should be 0,1,2.
At the same time I removed JSH_PIN0, because it is 0, and something - 0 gives something. That saved me 24 bytes.
I don't know what it else have influence on.

I hope you can integrate it in the next version.
C is difficult I must say.