void hilevel_handler_irq( ctx_t* ctx ) {
  PL011_putc( UART0, 'I', true );
  // read interupt IDentifier
  uint32_t id = GICC0->IAR;

  //handle interupt and clear timer
  if ( id == GIC_SOURCE_TIMER0 ) {
    scheduler( ctx ); TIMER0->Timer1IntClr = 0x01;
  }

  //write interupt identifier to signal
  GICC0->EOIR = id;

  return;
}