fix(ppp): Fix PPP not working after reboot if no RST (espressif#10264)

Modem will try to switch to CMUX and then back to COMMAND in order to allow communication with the modem.

Author: me-no-dev

libraries/PPP/src/PPP.cpp

@@ -324,8 +324,17 @@ bool PPPClass::begin(ppp_modem_model_t model, uint8_t uart_num, int baud_rate) {
  } else {
  // try to communicate with the modem
  if (esp_modem_sync(_dce) != ESP_OK) {
- log_v("Modem does not respond to AT, maybe in DATA mode? ...exiting network mode");
+ log_v("Modem does not respond to AT! Switching to COMMAND mode.");
  esp_modem_set_mode(_dce, ESP_MODEM_MODE_COMMAND);
+ if (esp_modem_sync(_dce) != ESP_OK) {
+ log_v("Modem does not respond to AT! Switching to CMUX mode.");
+ if (esp_modem_set_mode(_dce, ESP_MODEM_MODE_CMUX) != ESP_OK) {
+ log_v("Modem failed to switch to CMUX mode!");
+ } else {
+ log_v("Switching back to COMMAND mode");
+ esp_modem_set_mode(_dce, ESP_MODEM_MODE_COMMAND);
+ }
+ }
  if (esp_modem_sync(_dce) != ESP_OK) {
  log_e("Modem failed to respond to AT!");
  goto err;