Raspberry Pi Pico SDK¶

Just to be very clear and concise: The following instructions are not required to use the Arduino IDE with any RP2040-based boards. These instructions pertain to using only Raspberry Pi’s Pico SDK for RP2040 based boards.

Prerequisite¶

Follow Raspberry Pi’s “Getting Started with Pico” document to setup a proper development environment on your host PC (the machine that will build your project). Notice that the setup instructions are a little different for building on a Windows PC.

Either set an environment variable named PICO_SDK_PATH that points to your local clone of the pico-sdk or put the pico-sdk next to the RF24 folder or next to the folder containing your project using the RF24 library:

path/to/github/repos/
    pico-sdk/
    RF24/
    my_rf24_project/

Alternatively, the RF24 repository (and optionally the RF24Network and RF24Mesh repositories) can be included into your project’s “lib” folder as copies or git submodules. For more detail, see the below instructions to incorporate RF24 libs into your project.

Building the RF24 examples for the Pico SDK¶

Each example imports a set of constants (CE_PIN, CSN_PIN, IRQ_PIN) from the examples_pico/defaultPins.h file. Default values for SPI pins (SCK, MOSI, MISO) come from the Pico SDK repository’s pico-sdk/src/boards/include/boards/<board_name>.h files

1. Create a “build” directory in the RF24 repository’s root directory and navigate to it:

   cd RF24
   mkdir build
   cd build
   

2. Configure CMake for your desired build type and specific RP2040-based board

   cmake ../examples_pico -DCMAKE_BUILD_TYPE=Release -DPICO_BOARD=pico
   

   Or if building on a Windows PC:

   cmake -G "NMake Makefiles" ../examples_pico -DCMAKE_BUILD_TYPE=Release -DPICO_BOARD=pico
   

   The supported RP2040-based boards are listed in header files in the Pico SDK repository’s pico-sdk/src/boards/include/boards/<board_name>.h files. If the -DPICO_BOARD option is not specified, then the Pico SDK will default to building for the Raspberry Pi Pico board.

3. Build the examples using the CMakeLists.txt file located in the RF24/examples_pico directory.

   cmake --build . --config Release
   

   Notice we specified the build type again using the --config option.

Incorporating RF24 libs into your project¶

In order to use the RF24 libraries in your RP2040 based project:

1. Make a copy of the RF24 library (and optionally RF24Network and RF24Mesh libraries) in a “lib” directory located in your project’s root directory.

     path/to/my/project/
         lib/
             RF24/
             RF24Network/
             RF24Mesh/
         src/
             CMakeLists.txt
             ...
   

   Alternatively you can add the RF24* repositories as git submodules.

2. Include their CMakeLists.txt files from the RF24 libraries in your project’s top-level CMakeLists.txt file (usually located in the “src” directory). The following snippet assumes that your project’s “src” directory is on the same level as the previously mentioned “lib” directory.

   include(../lib/RF24/CMakeLists.txt)
   include(../lib/RF24Network/CMakeLists.txt)
   include(../lib/RF24Mesh/CMakeLists.txt)
   

3. In the same CMakeLists.txt file from step 2, add the RF24 libraries into the target_link_libraries configuration:

   target_link_libraries(${CMAKE_PROJECT_NAME}
       # ... Your project's other libraries ...
       RF24
       RF24Network
       RF24Mesh
   )
   

   If you are using tinyUSB, this line (or similar) should already exist:

   target_include_directories(${CMAKE_PROJECT_NAME} PRIVATE ${CMAKE_CURRENT_LIST_DIR})
   

4. Finally, remember to include the necessary RF24* libraries’ header files in your project’s source code where applicable.

   #include <RF24.h>
   #include <RF24Network.h>
   #include <RF24Mesh.h>
   

Using different pins for the SPI bus¶

Initially (without modification), the SPI bus uses the default pins defined in the Pico SDK repository’s pico-sdk/src/boards/include/boards/<board_name>.h files. However, there may be some boards that do not define the necessary pins to use as defaults. This can be rememdied using either project source code or build-time configuration.

Project Source code option¶

This option is the most reliable and flexible. It involves calling SPI.begin() and then passing the SPI object to RF24::begin(_SPI*).

#include <RF24.h>

RF24 radio(7, 8); // pin numbers connected to the radio's CE and CSN pins (respectively)
SPI spi;

int main()
{
    // again please review the GPIO pins' "Function Select Table" in the Pico SDK docs
    spi.begin(spi0, 2, 3, 4); // spi0 or spi1 bus, SCK, TX, RX

    if (!radio.begin(&spi)) {
        printf("Radio hardware is not responding!\n");
    }
    // continue with program as normal ...
}

Build-time configuration option¶

To specify the default SPI pins used at build time, you can use either:

1. declare these pins in the CMakeLists.txt file

   target_compile_definitions(${CMAKE_PROJECT_NAME}
       PUBLIC PICO_DEFAULT_SPI=0 # can only be 0 or 1 (as in `spi0` or `spi1`)
       PUBLIC PICO_DEFAULT_SPI_SCK_PIN=2 # depends on which SPI bus (0 or 1) is being used
       PUBLIC PICO_DEFAULT_SPI_TX_PIN=3  # depends on which SPI bus (0 or 1) is being used
       PUBLIC PICO_DEFAULT_SPI_RX_PIN=4  # depends on which SPI bus (0 or 1) is being used
   )
   

2. additional command line arguments

   cmake --build . --config Release -DPICO_DEFAULT_SPI=0 -DPICO_DEFAULT_SPI_SCK_PIN=2 -DPICO_DEFAULT_SPI_TX_PIN=3 -DPICO_DEFAULT_SPI_RX_PIN=4
   

Using Multiple Radios¶

It is possible to drive multiple nRF24L01 transceivers on a single board. To do this each radio needs dedicated digital output pins for the CE and CSN pins.

If you want to drive each radio with a separate SPI bus, then the following example will demonstrate how to do that.

#include <RF24.h>

// Declare the pin numbers connected to the radios' CE and CSN pins (respectively)
RF24 radio0(8, 5);   // first radio object
RF24 radio1(14, 13); // second radio object

// By default, one SPI bus instance is created by the RF24 lib. We'll use this
// default instance of the `spi0` interface for our first radio, but we want a
// different SPI bus for the second radio.
// 
// So, here we declare a second SPI bus instance:
SPI my_spi; // we specify the `spi1` bus interface below

bool setupRadios()
{
    // Initialize the first radio using the default SPI instance
    if (!radio0.begin()) {
        printf("Radio0 hardware is not responding!\n");
        return false;
    }
    // first radio object initialized successfully

    // specify the the second SPI bus interface and corresponding GPIO pins
    my_spi.begin(spi1, 10, 11, 12); // spi1 bus, SCK, TX, RX
    if (!radio1.begin(&my_spi)) {
        printf("Radio1 hardware is not responding!\n");
        return false;
    }
    // second radio object initialized successfully

    return true;
}

int main()
{
    stdio_init_all(); // init necessary IO for the RP2040

    while (!setupRadios()) { // if either radioX.begin() failed
        sleep_ms(1000); // add 1 second delay for console readability
        // hold program in infinite attempts to initialize the radios
    }

    // continue with program as normal ...
}