title: Will OS request interrupt to device?
body: <p>Take UART as an example.</p>
  
  <p>When UART received data, the UART device(chip) generates an interrupt, the SW interrupt handler will process this interrupt, ex: read data from HW buffer. This part is reasonable.</p>
  
  <p>For TX case, will OS/driver generate an interrupt to the device (UART chip) to let UART chip know there are some data need to send out?</p>