title: ESP32C3 prints to serial after reset despite no "uart_write_bytes(...)" calls
body: <p><strong>Situation:</strong></p>
  <p>An ESP32C3 running the Bluedroid BLE stack is connected via UART to another MCU which expects to <em>always</em> receive constant length messages. The system seems to work perfectly fine during normal operation, but if I for whatever reason reset the ESP32, the ESP32 writes exactly one byte to UART, hence throwing off the receiver MCU by one byte!</p>
  <p><strong>What I tried so far:</strong></p>
  <p>I commented out <em>any</em> call to <code>uart_write_bytes()</code>, which in turn ensures that my program is not at fault. This change doesn't help though, as the ESP32 still keeps printing the byte upon reset.</p>
  <p><strong>What the ESP send onto UART:</strong></p>
  <ul>
  <li>Upon hitting the &quot;RST&quot; button on the dev. board or flashing new software, it prints <code>0xfc</code>.</li>
  <li>If I unplug and replug the power however, it prints <code>0xf8</code>.</li>
  </ul>
  <p><strong>N.B.:</strong> I tried to reproduce such behavior on another microcontroller, specifically an STM32L552ZE. I was not able to, i.e. the STM32 didn't print anything to UART after resetting.</p>
  <p><strong>Configuration (sdkconfig.json):</strong>
  As the file was too long to paste it directly, you can find it on <a href="https://pastebin.com/ee49rSh7" rel="nofollow noreferrer">pastebin</a></p>
  <p><strong>Questions:</strong></p>
  <ol>
  <li>Is there some configuration option that causes the ESP32 to print that initial byte?</li>
  <li>How can I fix that behavior, i.e. make the ESP32 not print anything after resetting/flashing/startup</li>
  </ol>