[!SUCCESS] Contributing

Here is a list of the useful resources you want to read if you want to contribute to the project:

This page contains or will contain information you need to know when coding for Smoothie. TODO: make a proper introduction.

How to submit a pull request to the Smoothieware Github project

Config system and checksums

When to read configuration

When coding a Smoothie module, you probably want the user to be able to configure it. In Smoothie, configuration is stored in a configuration file, which is read at startup time (when your module is being loaded).

If you want your config values to be read only upon module loading, read your config values from the on_module_loaded callback of your module: example.


Consider a setting that looks like this in our config file:

maximum_death_star_hourly_power_consumption    100000000000

In our code, if we want to read it, we’ll do something like this:

void MyModule::on_config_loaded(void* argument){
	// Config does not actually work like that, this is just a hypothetical example to explain, Don't do it like this.
	this->maximum_power = this->kernel->config->value("maximum_death_star_hourly_power_consumption")->as_number();

To save flash storage space, we use Checksums: we don’t store the actual string, but a checksum of that string. We can compare the checksums of the configuration lines in the config file and still know if they correspond to our string.

An online tool to compute those when needed can be found here. The actual code for the checksum calculation is in src/libs/utils.cpp:

uint16_t get_checksum(string to_check){
   // From:
   uint16_t sum1 = 0;
   uint16_t sum2 = 0;
   for( int index = 0; index < to_check.length(); ++index ){
      sum1 = (sum1 + to_check[index]) % 255;
      sum2 = (sum2 + sum1) % 255;
   return (sum2 << 8) | sum1;

Now our code will look like this:

#define maximum_death_star_hourly_power_consumption_checksum CHECKSUM("maximum_death_star_hourly_power_consumption") 

void MyModule::on_config_loaded(void* argument){
	// Config works more like this
	this->maximum_power = this->kernel->config->value(maximum_death_star_hourly_power_consumption_checksum)->as_number();

Config value types

There are different types of config values you can retrieve from the config file. They are all strings, but there are convenience methods that allow you to convert them into other types.

ConfigValue object

This is not very useful. It’s what you get when you do:


You get an object of type ConfigValue. It stores the string (if the config option was found in the file) and has all kinds of convenience methods.


If your value is a string, you can access it using the as_string() method:

	this->whatever_option = this->kernel->config->value(whatever_checksum)->as_string();

Note: if you provided a default string, and the option is not found in the config file, that default will be returned. See below.


Converts your string to a double:

	double trouble = this->kernel->config->value(whatever_checksum)->as_number();

Note: if you provided a default number, and the option is not found in the config file, that default will be returned. See below.


This is convenient for stuff like:

void Laser::on_module_loaded() {
    if( !this->kernel->config->value( laser_module_enable_checksum )->by_default(false)->as_bool() ){ return; } 

This prevents the module from being loaded if the laser_module_enable config option is not present (defaults to false) or set to false explicitly.

“true” and “1” are valid true values, anything else is false.


Pin objects represent a pin configuration. They store the port number, the pin number, whether the pin is inverted, and other stuff. See: Pin.h.

They are generated from the result of as_string() (making default values as strings possible).

	this->step_pin = this->kernel->config->value(extruder_step_pin_checksum)->by_default("1.22")->as_pin()->as_output();


You can set a default value in case that option is not specified in the config file using the by_default() method, which can take either a string or a double. Doubles are used as defaults only by the as_number() and as_bool() methods.

	this->acceleration = this->kernel->config->value(acceleration_checksum)->by_default(1)->as_number();
	this->step_pin = this->kernel->config->value(extruder_step_pin_checksum)->by_default("1.22")->as_pin()->as_output();

If you want Smoothie to die if no config value is set in the config file, you can also use ->required(), but that’s mean.