Why not use printf all the time instead of pc.write?

Mostly for speed reasons! While incredibly powerful, printf can take milliseconds to print something, whereas pc.write takes microseconds. If you need to send a lot of information in a short period of time, you are better off using pc.write.

Consider the following example code:

#include "mbed.h"

static BufferedSerial pc(USBTX, USBRX);
Timer timeElapsed;

using namespace std::chrono;

int main()
{
    timeElapsed.start();
    
    char msg[] = "Hello World!\\n";
    pc.write(msg, sizeof(msg));
    
    timeElapsed.stop();

    // print time elapsed
    printf("The time taken was %llu milliseconds\\n", duration_cast<milliseconds>(timeElapsed.elapsed_time()).count());
    printf("The time taken was %llu microseconds\\n", duration_cast<microseconds>(timeElapsed.elapsed_time()).count());

    timeElapsed.reset();
    timeElapsed.start();
    printf("Hello World!\\n");
    timeElapsed.stop();

    printf("The time taken was %llu milliseconds\\n", duration_cast<milliseconds>(timeElapsed.elapsed_time()).count());
    

    while(1);
}

The serial monitor will output something that looks like this:

Hello World!
The time taken was 0 milliseconds
The time taken was 90 microseconds
Hello World!
The time taken was 14 milliseconds

Using pc.write took 90 microseconds whereas using printf took 14 milliseconds. That’s 155.55 times longer!

State Machine Best Practices

• Have an initialization state
• Never use blocking statements in a state machine (all operations must take less time than the tick time)
  • This includes transitions and state actions
• Transitions
  • Explicitly define all transitions (use “other” or else to catch remaining cases)
  • Make sure transition conditions are mutually exclusive
    • See Boolean Algebra Cheat Sheet for help (especially A + A’ = 1)

C++ Variable Keywords