Building a Package

Currently, the console doesn't have the ability to create packages automatically. This functionality is on the way. In the mean time, we will have to create the directory structure of a package ourselves.

A package is a collection of functions, like a dynamic library, that live on the device. The platform library, libflipper, knows about the functions that live in packages and can execute them remotely from any programming language.

Create a Package Directory

First, create a directory to house the files that will be built into a package for the device. We will call the package that we're creating in this example my_package.

mkdir my_package
cd my_package

Create the File Structure

Once inside, we need to create the necessary files so that Flipper's build system knows how to build the package. The directory tree for a package is below.

.
├── src
│   └── my_package.c
├── host
│   └── main.c
├── makefile
└── include
    └── my_package.h

mkdir src host include
touch src/my_package.c host/main.c include/my_package.h makefile

Populate the Makefile

# This sets the name of the Flipper package being built
MODULE := my_package

# This next line *MUST* come after MODULE has been set
include flipper.mk

Create your Functions

Next, we need to create a function in the src directory that will live on the device. We use a special macro called LF_FUNC to tell the flipper tools that this function should be marked as callable from outside the device. This macro only needs to be placed in front of the function's declaration, not the function's definition. That is to say, only place it in front of the function in the .c file.

include/main.h

#ifndef __my_package_h__
#define __my_package_h__

int my_package_function(void);

#endif

src/main.c

#include <my_package.h>

LF_FUNC int my_package_function(void) {
    return 1234;
} 

Create the Caller Code

A package isn't very useful unless we create a program that can call the functions inside of this. We use a folder called host to tell the flipper build system that code located inside of it should be build for the host platform. We can create a normal C program with a main function in this folder to test the execution of our my_package_function.

host/main.c

#include <flipper.h>
#include <my_package.h>

int main(int argc, char *argv[]) {

    flipper_attach();
    int value = my_package_function();
    printf("Got value %i from the package.\n", value); 

    return 0;
}

Build and Install

To build the package, simply

make

To install the package onto the attached hardware

make install

Run

The built products are placed in the build folder. Run the application by

./build/host/my_package

If all is well, you should see the following message printed on the command line.

./build/host/my_package
Got value 1234 from the package.

We can see that the value 1234 was retrieved as a result of calling the function on the device, obtaining its return value, and printing it.