lte: detect modem in ffh/recovery mode

when the LTE modem is in 'FFH' mode or in 'RECOVERY' mode, we can't use normal LTE functionality
the modem is normally brought into this state if a user starts a modem firmware update, but it is not completed successfully
the next logical step is to perform/finish the upgrade

FFH and RECOVERY are using 115200 baud. normal "FFF" modem firmware mode uses 921600.

So, when we do not get a response at 921600, but we do get a response at 115200, we advise the user to perform upgrade

esp32/lte/lteppp.c

@@ -444,6 +444,35 @@ void lteppp_resume(void) {
 /******************************************************************************
  DEFINE PRIVATE FUNCTIONS
  ******************************************************************************/
+bool trx_is_ok_or_error(){
+    if (strstr(lteppp_trx_buffer, "ERROR\r\n") != NULL){
+        // printf("ok\n");
+        return true;
+    } else if (strstr(lteppp_trx_buffer, "OK\r\n") != NULL) {
+        // printf("error\n");
+        return true;
+    }
+    return false;
+}
+
+/** check whether modem is responding at 115200
+ * this means it is in FFH or RECOVYER mode
+ */
+bool lteppp_check_ffh_mode(){
+    uart_set_baudrate(LTE_UART_ID, 115200);
+    uart_set_hw_flow_ctrl(LTE_UART_ID, UART_HW_FLOWCTRL_CTS_RTS, 64);
+    uart_set_rts(LTE_UART_ID, true);
+
+    for ( uint8_t attempt = 0 ; attempt < 3 ; attempt++ ){
+        lteppp_send_at_cmd("AT", LTE_PPP_BACK_OFF_TIME_MS);
+        if ( trx_is_ok_or_error() ){
+            // we could check for AT+SMOD / AT+BMOD to get more details
+            return true;
+        }
+    }
+    return false;
+}
+
 static void TASK_LTE (void *pvParameters) {
     MSG("\n");
     bool sim_present;
@@ -510,9 +539,14 @@ static void TASK_LTE (void *pvParameters) {
                     while(!lteppp_send_at_cmd("AT", LTE_RX_TIMEOUT_MIN_MS))
                     {
                         if (at_trials >= LTE_AT_CMD_TRIALS) {
-                            uart_set_hw_flow_ctrl(LTE_UART_ID, UART_HW_FLOWCTRL_DISABLE, 0);
-                            uart_set_rts(LTE_UART_ID, false);
+                            if ( lteppp_check_ffh_mode() ){
+                                lteppp_set_modem_conn_state(E_LTE_MODEM_RECOVERY);
+                            } else {
+                                uart_set_baudrate(LTE_UART_ID, MICROPY_LTE_UART_BAUDRATE);
+                                uart_set_hw_flow_ctrl(LTE_UART_ID, UART_HW_FLOWCTRL_DISABLE, 0);
+                                uart_set_rts(LTE_UART_ID, false);
                                 lteppp_set_modem_conn_state(E_LTE_MODEM_DISCONNECTED);
+                            }
                             xSemaphoreGive(xLTE_modem_Conn_Sem);
                             at_trials = 0;
                             goto modem_init;

esp32/lte/lteppp.h

@@ -61,7 +61,8 @@ typedef enum {
 typedef enum {
     E_LTE_MODEM_CONNECTED = 0,
     E_LTE_MODEM_CONNECTING,
-    E_LTE_MODEM_DISCONNECTED
+    E_LTE_MODEM_DISCONNECTED,
+    E_LTE_MODEM_RECOVERY
 } lte_modem_conn_state_t;
 
 #ifdef LTE_DEBUG_BUFF

esp32/mods/modlte.c

@@ -463,9 +463,13 @@ static mp_obj_t lte_init_helper(lte_obj_t *self, const mp_arg_val_t *args) {
         MP_THREAD_GIL_EXIT();
         xSemaphoreTake(xLTE_modem_Conn_Sem, portMAX_DELAY);
         MP_THREAD_GIL_ENTER();
-        if (E_LTE_MODEM_DISCONNECTED == lteppp_get_modem_conn_state()) {
+        lte_modem_conn_state_t modem_state = lteppp_get_modem_conn_state();
+        if (E_LTE_MODEM_DISCONNECTED == modem_state) {
+            xSemaphoreGive(xLTE_modem_Conn_Sem);
+            nlr_raise(mp_obj_new_exception_msg(&mp_type_OSError, "Couldn't start connection to Modem (modem_state=disconnected)"));
+        } else if (E_LTE_MODEM_RECOVERY == modem_state){
             xSemaphoreGive(xLTE_modem_Conn_Sem);
-            nlr_raise(mp_obj_new_exception_msg(&mp_type_OSError, "Couldn't connect to Modem (modem_state=disconnected)"));
+            nlr_raise(mp_obj_new_exception_msg(&mp_type_OSError, "Couldn't start connection to Modem (modem_state=recovery). Perform a modem firmware update."));
         }
         break;
     case E_LTE_MODEM_CONNECTING:
@@ -479,8 +483,11 @@ static mp_obj_t lte_init_helper(lte_obj_t *self, const mp_arg_val_t *args) {
     case E_LTE_MODEM_CONNECTED:
         //continue
         break;
+    case E_LTE_MODEM_RECOVERY:
+        nlr_raise(mp_obj_new_exception_msg(&mp_type_OSError, "Couldn't connect to Modem (modem_state=recovery). Perform a modem firmware update."));
+        break;
     default:
-        nlr_raise(mp_obj_new_exception_msg(&mp_type_OSError, "Couldn't connect to Modem (modem_state=default)"));
+        nlr_raise(mp_obj_new_exception_msg(&mp_type_OSError, "Couldn't connect to Modem (modem_state - default)"));
         break;
     }
     lte_obj.cid = args[1].u_int;