From 5470809c23bc8a860d909e0dd59e8b004d0f91c7 Mon Sep 17 00:00:00 2001
From: copercini <evandrocopercini@yahoo.com>
Date: Mon, 2 Oct 2017 15:45:52 -0300
Subject: [PATCH 1/2] Print error when serial number is invalid

---
 cores/esp32/HardwareSerial.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/cores/esp32/HardwareSerial.cpp b/cores/esp32/HardwareSerial.cpp
index a053bf227cf..efcefda66a2 100644
--- a/cores/esp32/HardwareSerial.cpp
+++ b/cores/esp32/HardwareSerial.cpp
@@ -14,6 +14,10 @@ void HardwareSerial::begin(unsigned long baud, uint32_t config, int8_t rxPin, in
     if(_uart) {
         end();
     }
+    if(0 > _uart_nr || _uart_nr > 2) {
+        log_e("Serial number is invalid, please use 0, 1 or 2");
+        end();
+    }
     if(_uart_nr == 0 && rxPin < 0 && txPin < 0) {
         rxPin = 3;
         txPin = 1;

From ce419a003fcb207550ea180dfcc593a1aae19589 Mon Sep 17 00:00:00 2001
From: copercini <evandrocopercini@yahoo.com>
Date: Tue, 3 Oct 2017 09:43:26 -0300
Subject: [PATCH 2/2] Move to the first check, change end by return

---
 cores/esp32/HardwareSerial.cpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/cores/esp32/HardwareSerial.cpp b/cores/esp32/HardwareSerial.cpp
index efcefda66a2..500bff46fdd 100644
--- a/cores/esp32/HardwareSerial.cpp
+++ b/cores/esp32/HardwareSerial.cpp
@@ -11,11 +11,11 @@ HardwareSerial::HardwareSerial(int uart_nr) : _uart_nr(uart_nr), _uart(NULL) {}
 
 void HardwareSerial::begin(unsigned long baud, uint32_t config, int8_t rxPin, int8_t txPin)
 {
-    if(_uart) {
-        end();
-    }
     if(0 > _uart_nr || _uart_nr > 2) {
         log_e("Serial number is invalid, please use 0, 1 or 2");
+        return;
+    }
+    if(_uart) {
         end();
     }
     if(_uart_nr == 0 && rxPin < 0 && txPin < 0) {