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Building for FreeRTOS

This document covers building Ioto with FreeRTOS. Please read the General Building for general background first.

Requirements

Ioto on the FreeRTOS has the following requirements for the target hardware:

  • TLS stack
  • A flash file system
  • 32-bit CPU
  • 2MB RAM

The flash file system such as LittleFS is required to store database and configuration data.

The instructions below assume you have your development environment setup with FreeRTOS installed and you have successfully built one of the FreeRTOS demo applications for your target device.

Ioto requires a TLS stack for secure network communications. Ioto support MbedTLS and OpenSSL. See Building TLS for details.

Please read Supported Hardware for a complete target hardware list.

Download Ioto

Navigate to the Builder site and select Products in the sidebar menu and click on the download link for the Ioto Evaluation.

Extract the Ioto source code into your FreeRTOS app directory and rename the ioto-VERSION director to ioto.

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tar xvfz ioto-VERSION.tgz
mv ioto-* ioto

Preparing Ioto Source

Before building your Ioto source code, you need to configure Ioto for your desired set of services. The Ioto distribution build includes several demo apps that define a set of services required for that app. The Ioto services are selected via the ioto.json5 configuration file. The services are:

Service Description
database Enable the embedded database
keys Get AWS IAM keys for local AWS API invocation (dedicated clouds only)
logs Capture log files and send to AWS CloudWatch logs (dedicated clouds only)
mqtt Enable MQTT protocol
provision Dynamically provision keys and certificates for cloud based management
register Register with the Ioto Builder
serialize Run a serialization service when making the device
shadow Enable AWS IoT shadow state storage
sync Enable transparent database synchronization with the cloud
url Enable client HTTP request support
web Enable the local embedded web server

The included apps are:

Name Directory Description
auth Simple embedded web server user/group authentication.
blink Minimal ESP32 blink app to demonstrate linking with Ioto on ESP32 microcontrollers.
demo Cloud-based management of a device. Demonstrates simple data synchronization and metrics.
eco Customized cloud-based device management of an Eco House demo app.

The default app is the demo app which sends device data and metrics to the cloud. The eco app emulates a simple Home charging networks and a mobile app.

To select an app, invoke make config with your desired APP:

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make APP=demo config

This will copy the app's configuration to the ioto/config directory. From there, you can copy the config files to your Flash file system.

If you want a complete sample, please see the Building ESP32 for a demo app that uses FreeRTOS on ESP32 hardware micro-controllers.

Embedding Ioto

To invoke the Ioto library from your main program you will need to include the ioto.h header in your source and call Ioto APIs to initialize and run.

In your main program, use:

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#include "ioto.h"

int main() {
    //  Start the Ioto runtime
    ioStartRuntime(1);

    //  Run Ioto services until instructed to exit
    //  You need to call vTaskStartScheduler() before ioRun
    ioRun();

    ioStopRuntime();
}

int iotStart() {
    //  This is invoked by ioRun when Ioto is ready
    //  Put your user code here
}

void iotStop() {
    //  This is invoked by ioRun when Ioto is shutting down
}

Building Ioto and FreeRTOS

The Ioto source files are contained in the ioto/lib directory which contains C files and one assembly file. The assembly code contains some high performace stack management code that is used on Arm, Mips, RiscV and X86 platforms.

To build your FreeRTOS application with Ioto, edit the FreeRTOS app Makefile and add the following lines. This will cause the Makefile to build the Ioto source code when compiling FreeRTOS.

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// Must be after the OBJ_FILES definition

C_FILES     = $(wildcard ioto/lib/*.c)
A_FILES     = $(wildcard ioto/lib/*.S)
OBJ_FILES   += $(C_FILES:%.c=$(BUILD_DIR)/%.o)
OBJ_FILES   += $(A_FILES:%.S=$(BUILD_DIR)/%.o)
CFLAGS      += -Iioto/include -I/path/to/openssl/include
LDFLAGS     += -L/path/to/openssl/lib -lssl -lcrypto

Use the following if you are using MbedTLS

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CFLAGS  += -I/path/to/mbedtls/include
LDFLAGS += -L/path/to/mbedtls -lmbedtls -lmbedcrypto -lmbedx509

Then build with make

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$ make

Filesystem

Ioto requires a flash file system with a Posix API to store config and state files. The file system should be defined with the following directories and files:

Directory Description
state Runtime state including database, provisioning data and provisioned certificates
File Description
ioto.json5 Primary Ioto configuration file
web.json5 Local web server configuration file
schema.json5 Database schema
device.json5 Per-device definition
roots.crt Top-level roots certificate
aws.crt AWS root certificate

Copy the state files to your flash file system.

Local Management

If the selected app enables the embedded web server, files will be served from the site directory. The Ioto embedded web server is configured via the config/web.json5 configuration file which is then copied to the config/web.json5 directory.

Tech Notes

The stack size is configured to be 32K for the main app task and for spawned fiber tasks. Observationally, the minimum stack for the core Ioto is ~14K.

Ioto uses its own optimized printf implementation which uses less stack (<1K) and is more secure, being tolerant of errant NULL arguments.