Make RPC example easier to understand

Author: sebromero

libraries/RPC/examples/RPC_m4/RPC_m4.ino

@@ -1,58 +1,110 @@
 #include "Arduino.h"
 #include "RPC_internal.h"
 
-#ifdef CORE_CM7
-int add(int a, int b) {
- printf("calling add on M7\n");
- delay(1000);
+using namespace rtos;
+
+Thread subtractThread;
+
+/**
+ * Returns the CPU that's currently running the sketch (M7 or M4)
+ * Note that the sketch has to be uploaded to both cores. 
+ **/
+String currentCPU() {
+ if (HAL_GetCurrentCPUID() == CM7_CPUID) {
+ return "M7";
+ } else {
+ return "M4";
+ }
+}
+
+/**
+ * Adds two numbers and returns the sum
+ **/
+int addOnM7(int a, int b) {
+ Serial.println(currentCPU() + ": executing add with " + String(a) + " and " + String(b));
+ delay(700); // Simulate work
  return a + b;
 }
-int subtract(int a, int b) {
- printf("calling subtract on M7\n");
+
+/**
+ * Subtracts two numbers and returns the difference
+ **/
+int subtractOnM7(int a, int b) {
+ Serial.println(currentCPU() + ": executing subtract with " + String(a) + " and " + String(b));
+ delay(700); // Simulate work
  return a - b;
 }
-#endif
-
-rtos::Thread t;
 
-void call_substract() {
- while (1) {
- delay(700);
- RPC1.print("Calling subtract ");
- auto res = RPC1.call("sub", 12, 45).as<int>();;
- RPC1.println(res);
+void callSubstractFromM4() {
+ while (true) {
+ delay(700); // Wait 700ms with the next calculation
+ int a = random(100); // Generate a random number
+ int b = random(100); // Generate a random number
+ RPC1.println(currentCPU() + ": calling subtract with " + String(a) + " and " + String(b));
+ 
+ auto result = RPC1.call("remoteSubtract", a, b).as<int>();
+ // Prints the result of the calculation
+ RPC1.println(currentCPU() + ": Result is " + String(a) + " - " + String(b) + " = " + String(result));
  }
 }
 
 void setup() {
- // put your setup code here, to run once:
+
+ pinMode(LED_BUILTIN, OUTPUT);
+
+ // Initialize RPC library; this also boots the M4 core
  RPC1.begin();
  Serial.begin(115200);
- //while (!Serial) {}
- //Serial.begin(115200);
- pinMode(LED_BUILTIN, OUTPUT);
-#ifdef CORE_CM7
- RPC1.bind("add", add);
- RPC1.bind("sub", subtract);
-#else
- t.start(call_substract);
-#endif
+ //while (!Serial) {} // Uncomment this to wait until the Serial connection is ready
+
+ // Both CPUs will execute this instruction, just at different times
+ randomSeed(analogRead(A0)); // Initializes the pseudo-random number generator
+
+ if (currentCPU() == "M7") {
+ // M7 CPU becomes the server, so it makes two functions available under the defined names
+ RPC1.bind("remoteAdd", addOnM7);
+ RPC1.bind("remoteSubtract", subtractOnM7);
+ } 
+
+ if (currentCPU() == "M4") {
+ // M4 CPU becomes the client, so spawns a thread that will call subtractOnM7() every 700ms
+ subtractThread.start(callSubstractFromM4);
+ }
 }
 
 void loop() {
- // put your main code here, to run repeatedly:
-#ifndef CORE_CM7
- digitalWrite(LED_BUILTIN, HIGH);
- delay(1000);
- digitalWrite(LED_BUILTIN, LOW);
- delay(1000);
-
- RPC1.print("Calling add ");
- auto res = RPC1.call("add", 12, 45).as<int>();;
- RPC1.println(res);
-#else
- while (RPC1.available()) {
- Serial.write(RPC1.read());
+
+ if (currentCPU() == "M4") {
+ // On M4 let's blink an LED. While it's blinking, the callSubstractFromM4() thread is running, 
+ // so it will execute roughly 3 times (2000 / 700 ms)
+ digitalWrite(LED_BUILTIN, LOW);
+ delay(1000);
+ digitalWrite(LED_BUILTIN, HIGH);
+ delay(1000);
+
+ int a = random(100);
+ int b = random(100);
+ // PRC.print works like a Serial port, but it needs a receiver (in this case the M7) 
+ // to actually print the strings to the Serial port
+ RPC1.println(currentCPU() + ": calling add with " + String(a) + " and " + String(b));
+ // Let's invoke addOnM7() and wait for a result.
+ // This will be delayed by the forced delay() in addOnM7() function
+ // Exercise: if you are not interested in the result of the operation, what operation would you invoke?
+ auto result = RPC1.call("remoteAdd", a, b).as<int>(); 
+ RPC1.println(currentCPU() + ": Result is " + String(a) + " + " + String(b) + " = " + String(result));
  }
-#endif
+ 
+ if (currentCPU() == "M7") {
+ // On M7, let's print everything that is received over the RPC1 stream interface
+ // Buffer it, otherwise all characters will be interleaved by other prints
+ String buffer = "";
+ while (RPC1.available()) {
+ buffer += (char)RPC1.read(); // Fill the buffer with characters
+ }
+
+ if (buffer.length() > 0) {
+ Serial.print(buffer);
+ }
+ }
+
 }