libraries/RPC: Fix and update examples.

- Fix serial pass-through example.
- Add MD5 checksum example.
- Add RAW-channel ping-pong example.

Signed-off-by: iabdalkader <i.abdalkader@gmail.com>

Author: iabdalkader

libraries/RPC/examples/MD5_Checksum/MD5_Checksum.ino

@@ -59,6 +59,7 @@ void setup() {
     #ifdef CORE_CM4
     RPC.bind("set_buffer_size", set_buffer_size);    
     #else
+    delay(100);
     auto ret = RPC.call("set_buffer_size", data_buf_size).as<size_t>();
     #endif
 

libraries/RPC/examples/PingPong_RAW/PingPong_RAW.ino

@@ -43,7 +43,7 @@ void loop() {
     Serial.print("=> ");
     Serial.write(buf, sizeof(buf));
     Serial.println();
-    RPC.write(&buf[0], sizeof(buf), false, true);
+    RPC.write(&buf[0], sizeof(buf));
     delay(100);
     #endif
 }

libraries/RPC/examples/SerialPassthrough_RPC/SerialPassthrough_RPC.ino

@@ -3,22 +3,18 @@
 
 void setup() {
   Serial.begin(115200);
+  while (!Serial) {
+  }
   RPC.begin();
 }
 
 void loop() {
-  String data = "";
-  while (RPC.available()) {
-    data += (char)RPC.read();
-  }
-  if (data != "") {
-    Serial.write(data.c_str(), data.length());
-  }
-  data = "";
-  while (Serial.available()) {
-    data += (char)Serial.read();
-  }
-  if (data != "") {
-    RPC.write(data.c_str(), data.length());
+  if (HAL_GetCurrentCPUID() == CM4_CPUID) {
+    RPC.println("Printed from M4 core");
+    delay(1000);
+  } else {
+    while (RPC.available()) {
+      Serial.print((char) RPC.read());
+    }
   }
 }