title: Read signal level for ppp connection on RasPI
body: <p>I have a RasPI 3 with SIM800L connected via UART.</p>
  <p>I use PPP connection to enable network traffic, and I want to get the signal level via AT command but device is busy when PPP is on.</p>
  <p>Is it possibile to access to signal level? Or send a AT commands?</p>