CAN: Loopback() (#286)

* Add: loopback()
Todo: comments some part can be improved...

* Add: Loopback example sketch

* Docu: change for loopback() and update version

* Style: format theCAN lib with Clang formatter

* Fix: PWM pin defines of XMC1400 2go

libraries/CAN/README_CAN.md

@@ -205,7 +205,7 @@ if ((packetId & mask) == id) {
 
 Returns `1` on success, `0` on failure.
 
-<strike>
+
 ## Other modes
 
 ### Loopback mode
@@ -216,6 +216,7 @@ Put the CAN controller in loopback mode, any outgoing packets will also be recei
 CAN.loopback();
 ```
 
+<strike>
 ### Sleep mode
 
 Put the CAN contoller in sleep mode.
@@ -233,8 +234,5 @@ CAN.wakeup();
 
 # Develop notes
 
-## XMCLibs Version
-For CAN development, we use v4.3.0 of XMClib. But other source code stay 2.1.16. Need to be fixed and updated in the future!!
-
 ## CAN macro
 Because XMClibs use CAN macro, conflicts with Arduino default CAN class name, so we manually changed XMClib (CAN -> CAN_xmc). Automatic patch might be needed in the future. 

libraries/CAN/examples/CANLoopBack/CANLoopBack.ino

@@ -0,0 +1,61 @@
+// Copyright (c) Linjing Zhang. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+#include <CAN.h>
+using namespace ifx;
+
+void setup() {
+  // put your setup code here, to run once:
+  Serial.begin(9600);
+  while (!Serial)
+    ;
+
+  Serial.println("CAN Loopback");
+
+  // start the CAN bus at 500 kbps
+  if (!CAN.begin(500E3)) {
+    Serial.println("Starting CAN failed!");
+    while (1)
+      ;
+  }
+
+  // set the can in loopback mode
+  CAN.loopback();
+}
+
+void loop() {
+
+  //
+  Serial.print("Sending packet");
+  CAN.beginPacket(0x12);
+  CAN.write('L');
+  CAN.write('O');
+  CAN.write('O');
+  CAN.write('P');
+  CAN.endPacket();
+
+
+  int packetSize = CAN.parsePacket();
+
+  if (packetSize) {
+    // received a packet
+    Serial.print("Received ");
+
+    if (CAN.packetExtended()) {
+      Serial.print("extended ");
+    }
+
+    Serial.print("packet with id 0x");
+    Serial.print(CAN.packetId(), HEX);
+
+    Serial.print(" and length ");
+    Serial.println(packetSize);
+
+    while (CAN.available()) {
+      Serial.print((char)CAN.read());
+    }
+    Serial.println();
+  }
+
+  delay(1000);
+}