Creating Your Own Platform

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Version: [ , master , 2024.10 , 2023.06 , 2023.02 , 2022.12 , 2022.09 ]

Creating your own platform can be a good way of saving work by …

  • Tailoring a config that is specific to your product or project!
  • To make sure you have sensible default values for parameters
  • Or to make sure that the initialization is done correctly

If you contribute it to the main Bitcraze repository it is also a way to distribute your work! So how do you do it? Follow these steps!

Add your platform to Kconfig

To make it possible to select your platform for the build you need to add it to a Kconfig file. You can find the platform selection in the root Kconfig file.

Right now the selction looks like:

menu "Platform configuration"

choice
    prompt "Platform to build"
    default CONFIG_PLATFORM_CF2

config PLATFORM_CF2
    bool "Build for CF2"
    select SENSORS_BMI088_BMP388
    select SENSORS_MPU9250_LPS25H

config PLATFORM_BOLT
    bool "Build for Bolt"
    select SENSORS_BMI088_BMP388
    select SENSORS_BMI088_SPI

config PLATFORM_TAG
    bool "Build for the roadrunner"
    select SENSORS_BMI088_BMP388

endchoice

Let’s add our own platform, RINCEWIND, which has the same sensors as the Bolt.

menu "Platform configuration"

choice
    prompt "Platform to build"
    default CONFIG_PLATFORM_CF2

config PLATFORM_CF2
    bool "Build for CF2"
    select SENSORS_BMI088_BMP388
    select SENSORS_MPU9250_LPS25H

config PLATFORM_BOLT
    bool "Build for Bolt"
    select SENSORS_BMI088_BMP388
    select SENSORS_BMI088_SPI

config PLATFORM_TAG
    bool "Build for the roadrunner"
    select SENSORS_BMI088_BMP388

config PLATFORM_RINCEWIND
    bool "Build for the Rincewind platform"
    select SENSORS_BMI088_BMP388
    select SENSORS_BMI088_SPI

endchoice

This creates the CONFIG_PLATFORM_RINCEWIND variable, usable both from C code as a define (when you include autoconf.h) as well as an environment variable usable from the Makefiles and the Kbuild files.

Add a init source file to Kbuild

We need to add a entry point for your platform. The way the build system determines which platform init file to include is found in the src/platform/src/Kbuild file:

obj-$(CONFIG_PLATFORM_BOLT) += platform_bolt.o
obj-$(CONFIG_PLATFORM_CF2) += platform_cf2.o
obj-$(CONFIG_PLATFORM_TAG) += platform_tag.o
obj-y += platform.o
obj-y += platform_stm32f4.o
obj-y += platform_utils.o

Let’s add RINCEWIND:

obj-$(CONFIG_PLATFORM_BOLT) += platform_bolt.o
obj-$(CONFIG_PLATFORM_CF2) += platform_cf2.o
obj-$(CONFIG_PLATFORM_TAG) += platform_tag.o
obj-$(CONFIG_PLATFORM_RINCEWIND) += platform_rincewind.o
obj-y += platform.o
obj-y += platform_stm32f4.o
obj-y += platform_utils.o

We will base the src/platform/src/platform_rincewind.c file on the bolt:

#define DEBUG_MODULE "PLATFORM"

#include <string.h>

#include "platform.h"
#include "exti.h"
#include "nvic.h"
#include "debug.h"

static platformConfig_t configs[] = {
#ifdef CONFIG_SENSORS_BMI088_SPI
  {
    .deviceType = "CB10",
    .deviceTypeName = "Rincewind",
    .sensorImplementation = SensorImplementation_bmi088_spi_bmp388,
    .physicalLayoutAntennasAreClose = false,
    .motorMap = motorMapBoltBrushless,
  }
#endif
};

const platformConfig_t* platformGetListOfConfigurations(int* nrOfConfigs) {
  *nrOfConfigs = sizeof(configs) / sizeof(platformConfig_t);
  return configs;
}

void platformInitHardware() {
  // Low level init: Clock and Interrupt controller
  nvicInit();

  // EXTI interrupts
  extiInit();
}

const char* platformConfigGetPlatformName() {
  return "Rincewind";
}

The platformInitHardware() and platformGetListOfConfigurations() functions is called by platform.c as part of general init of the device.

Add platform default parameter values

Your platform need to define suitable default values to (persistent) parameters. To do this we will need to create a src/platform/interface/platform_rincewind.h and make sure that this gets included when we build for the RINCEWIND platform. This is done by adding to the src/platform/interface/platform_defaults.h:

#pragma once

#define __INCLUDED_FROM_PLATFORM_DEFAULTS__

#ifdef CONFIG_PLATFORM_CF2
    #include "platform_defaults_cf2.h"
#endif
#ifdef CONFIG_PLATFORM_BOLT
    #include "platform_defaults_bolt.h"
#endif
#ifdef CONFIG_PLATFORM_TAG
    #include "platform_defaults_tag.h"
#endif

Becomes:

#pragma once

#define __INCLUDED_FROM_PLATFORM_DEFAULTS__

#ifdef CONFIG_PLATFORM_CF2
    #include "platform_defaults_cf2.h"
#endif
#ifdef CONFIG_PLATFORM_BOLT
    #include "platform_defaults_bolt.h"
#endif
#ifdef CONFIG_PLATFORM_TAG
    #include "platform_defaults_tag.h"
#endif
#ifdef CONFIG_RINCEWIND
    #include "platform_defaults_bolt.h"
    #include "platform_defaults_rincewind.h"
#endif

We base it on the default parameters for the Bolt. To determine how to add content to platform_defaults_rincewind.h please check what is added to the existing platforms.

Add a platform default config

To make it easier for people to build for RINCEWIND we can add a defconfig for it. This is done by adding a file in the configs/ folder. Let us look at bolt_defconfig:

CONFIG_PLATFORM_BOLT=y

CONFIG_ESTIMATOR_AUTO_SELECT=y
CONFIG_CONTROLLER_AUTO_SELECT=y

Based on this a start of rincewind_defconfig could be:

CONFIG_PLATFORM_RINCEWIND=y

CONFIG_ESTIMATOR_AUTO_SELECT=y
CONFIG_CONTROLLER_AUTO_SELECT=y

Then RINCEWIND platform could be built by:

$ make rincewind_defconfig
make[1]: Entering directory '/home/jonasdn/sandbox/kbuild-firmware/build'
  GEN     ./Makefile
#
# configuration written to .config
#
make[1]: Leaving directory '/home/jonasdn/sandbox/kbuild-firmware/build'
$ make -j 12
[...]

Need a different power distribution?

Suppose our new platform is a car with 4 wheels, then we will need a new power distribution function, that is the translation from roll, pitch and yaw to motor power. The default implementation can be found in src/modules/src/power_distribution_quadrotor.c but now we need to write a new function that works for cars.

The first step is to add a car power distrbution setting to the configuration. In the standard configuration, the quadrotor power distribution is the only option and it is used by all platforms. Edit src/modules/src/Kconfig and find the location where the power distribution is configured

choice
    prompt "Type of power distribution"
    default POWER_DISTRIBUTION_QUADROTOR

config POWER_DISTRIBUTION_QUADROTOR
    bool "Quadrotor power distribution"
    depends on PLATFORM_CF2 || PLATFORM_BOLT || PLATFORM_TAG
    help
        Power distribution function for quadrotors

endchoice

Now add a new car distribution setting and make it available for your platform.

choice
    prompt "Type of power distribution"
    default POWER_DISTRIBUTION_QUADROTOR

config POWER_DISTRIBUTION_QUADROTOR
    bool "Quadrotor power distribution"
    depends on PLATFORM_CF2 || PLATFORM_BOLT || PLATFORM_TAG
    help
        Power distribution function for quadrotors

config POWER_DISTRIBUTION_CAR
    bool "Car power distribution"
    depends on PLATFORM_RINCEWIND
    help
        Power distribution function for cars

endchoice

The next step is to add an implementation of the power distribution function. Copy power_distribution_quadrotor.c into a new file, power_distribution_car.c and modify the powerDistribution() function to fit your needs. Also modify the powerDistributionCap(), this function is responsible for limiting the thrust to the valid range [0 - UINT16_MAX].

The final step is to add the c file to the build. Open src/modules/src/Kbuild and add your new file.

obj-$(CONFIG_POWER_DISTRIBUTION_CAR) += power_distribution_car.o

And you are done! You have created your own platform, good job!