rp2040-pico-command-line-interpreter

This is a work in progress. This project assumes that you are using the C/C++ SDK for the Pico. I am using VS Code on Manjaro Linux. I compile my code on an attached Raspberry Pi Zero (where the SDK is installed and my project code lives).

I wanted to create a command line interpreter for the Raspberry Pi Pico (rp2040) with the idea that a programmer could simply add code into a couple "C" source files, recompile, and the programmer would be able to run those commands in a pseudo shell like environment. The idea could be used to create your own REPL if you wanted.

As an example, suppose I wanted to test several routines that I wrote to use different sensors. Instead of having several programs, I could have just one and use commands to execute them. If I wanted to blink an LED on a certain pin, I could run a command like the following from the command line interpreter:

$blink_led 25 10 250
OK

$

The programmer defines a routine in a "C" source file (user_funcs.c) and accompanying header file (user_funcs.h).

This would be added to the file user_funcs.c

void blink_led(char tokens[][MAX_STRING_SIZE]) {

  uint8_t LED_PIN = atoi(tokens[1]);
  if (LED_PIN == 0) {
    console_puts("\nNot a valid pin number.\n");
    return;
  } // end if

  uint16_t iters = atoi(tokens[2]);
  if (iters == 0) {
    console_puts("\nNot a valid number for iterations.\n");
    return;
  } // end if

  uint16_t millis = atoi(tokens[3]);
  if (millis == 0) {
    console_puts("\nNot a valid number for duration.\n");
    return;
  } // end if

  gpio_init(LED_PIN);
  gpio_set_dir(LED_PIN, GPIO_OUT);

  for (int i = 0; i < iters; i++) {
    gpio_put(LED_PIN, 1);
    sleep_ms(millis);
    gpio_put(LED_PIN, 0);
    sleep_ms(millis);
  } // end for

} // end blink_led

The parameters are passed in as an array of string tokens. The tokens are gathered in the main program, but the programmer shouldn't worry about this. These are the arguments to the command line command. The command name is tokens[0]. In the example code above, the arguments are the LED pin - tokens[1], the number of times to blink - tokens[2], and the duration of the blink (in milliseconds) - tokens[3].

The command blink_led also has to be added to an intialization routine. The three pieces of information are the command name, command help, and the function name.

This also needs modifying in user_funcs.c

// Each user function you create, you must also
// add to the init_user_functions routine.
void init_user_functions() {
  // This is my first user-defined function. I give
  // the command a name - in this case "blink_led".
  // You can supply a short help description. And, 
  // then, I point the user_functions struct array
  // to the actual name of my user-defined function.
  strcpy(user_functions[0].command_name, "blink_led");
  strcpy(user_functions[0].command_help,
         "blink_led pin_number iterations duration (ms)");
  user_functions[0].user_function = blink_led;

  // Here is a second user function.
  strcpy(user_functions[1].command_name, "read_pir_sensor");
  strcpy(user_functions[1].command_help,
         "read_pir_sensor pin_number iterations");
  user_functions[1].user_function = read_pir_sensor;

  //Here is a third user function.
  strcpy(user_functions[2].command_name, "calc");
  strcpy(user_functions[2].command_help, "calc math_expression");
  user_functions[2].user_function = calc;
} // init_user_functions

Finally, the function needs to be added to the accompanying header file (user_funcs.h).

void blink_led(char tokens[][MAX_STRING_SIZE]);
void read_pir_sensor(char tokens[][MAX_STRING_SIZE]);
void calc(char tokens[][MAX_STRING_SIZE]);

This should be all the programmer has to worry about. Run the make command in the build directory and then copy the .uf2 file to the Pico. The command line interpreter should start to run with the prompt "$" waiting for you to type a command to run. There is a list command to list the user-defined functions. Just for fun, I added a calc command, which uses the TINYEXPR - Tiny recursive descent parser and evaluation engine in C. So, you can do things like:

$calc sqrt(1256)+1256^3

1.981385e+09

OK

$