AliOS Things Technical Overview
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AliOS Things is Alibaba's IoT version of AliOS Family, it was announced in The Computing Conference 2017 in Hangzhou by Alibaba Cloud, and open sourced in 20th, October, 2017 at github:https://github.com/alibaba/AliOS-Things.
From an architectural point of view, AliOS Things adapts Layered Architecture and Component Architecture. From bottom to top, AliOS Things includes:
- BSP: Board Support Package mainly developed and maintained by SoC Vendor
- HAL: Hardware Abstraction Layer, like WiFi, UART
- Kernel: Rhino RTOS Kernel, Yloop, VFS, KV Storage included
- Protocol Stack: LwIP TCPIP Stack, uMesh mesh networking stack included
- Security: TLS, TFS(Trusted Framework Service), TEE(Trusted Exexcution Environment)
- AOS API: AliOS Things exposed APIs for Application and Middleware
- Middleware: Alibaba's value-added and commonly seen IoT components included
- Examples: hands-on sample codes, and well tested applications such as Alinkapp
All modules have been organized as Components, and each component has its own .mk file to describe its dependency with other Components, which enables applications to choose components needed easily.
| Folder Name | Description |
|---|---|
| board | evaluation board such as STM32L496G-Discovery |
| build | build infrastructure |
| device | peripherals connected to MCU/SoC, such as Serial WiFi Module utilizing AT |
| example | hands-on sample codes, well tested industry application such as alinkapp |
| framework | IoT common components |
| include | system include headers |
| kernel | including Rhino, Protocol Stack |
| platform | including arch holding cpu related files, mcu holding SoC special files |
| security | security components including TLS/TFS/TEE |
| tools | cli and testbed for constructing remote device center |
| utility | IoT common libraries such as cjson |
| test | UT testcases |
Rhino is in-house designed and developed by AliOS Things team. It is characterized by ultra-small footprint, low power consumption, real time, multitasking.
Rhino provides rich kernel primitives including buffer queue, ring buffer, timer, semaphore, mutex, fifo, event etc.
Rhino provides both static and dynamic allocation for most of the kernel objects. A memory allocator designed for small memory block management, can support both fixed block and variable block. It can also multiple memory region.
Most of the kernel features such as work queue, and memory allocator could be configurable inor out by per-build file named k_config.h.
With the ability to scale component in and out, Rhino could make the final image as small as possible, which could be programmed into device with very same flash size.
For the IOT device, it’s important to consider the power consumption for hardware because the buffer of power is limited. The faster the system consumes the power, the shorter the live time of it will be. Rhino kernel provides tickles idle mode of CPU to help system save the power and extend its live time.
Normally, When CPU has nothing to do, it will execute a native instruction of the processor (WFI for ARM, HLT for IA32-bit processors) to enter a low power state, when the CPU register context is maintained, and system tick clock interrupts wakes up the CPU at every tick moment.
To save more power than normal, Rhino kernel provides tickles idle mode of CPU. When OS detect there is nothing to do in feature within a fixed duration (multiple ticks or more long), it was called tickles idle time. At that time, the system tick clock is programmed to fire interrupt in tickless idle time and put CPU into C1 state(CPU execute a native instruction, WFI for ARM, HLT for IA 32-bit processors), from that point there is no system tick clock interrupt happen anymore. The system tick count stops increasing and CPU is in low power mode(C1) until tickless idle time passed, when the system tick timer interrupt is fired again to wakeup CPU from C1 to C0 state, and passed ticks is compensated to system tick count.
Rhino provides two scheduling policy, priority-based/preemptive scheduling and round-robin scheduling. For both scheduling policy, the highest priority task is always preferred for scheduling.
A priority-based preemptive scheduler preempts the CPU when a task has a higher priority than the current task running. This means that if a task with a higher priority than that of the current task becomes ready to run, the kernel immediately saves the current task's context, and switches to the context of the higher priority task.Thus, the kernel ensures that the CPU is always allocated to the highest priority task that is ready to run.
A round-robin scheduler shares the CPU amongst these tasks by using time-slicing. Each task in a group of tasks with the same priority is arranged to execute for a defined interval, or time slice, before relinquishing the CPU to the next task in the group. None of them, therefore, can usurp the processor until it is blocked. When the time slice expires, the task moves to last place in the ready queue list for that priority.
Rhino can support stack overflow, memory leak, memory corruption detection which helps developer figure out root cause of difficult issues. Cooperating with AliOS Studio IDE, Rhino's trace function help visualize overall system activities.
Yloop is an asynchronous event framework, highly considering libuv and event loop used in Embedded world. Yloop provide a mechanism to handle IO(mainly socket), timer, system events, user events in a single task, which greatly reduces memory usage while avoiding the complexity of multi-threading programming.
Yloop instance is bound to task context. Multiple Yloop instances can be created, and each is bound to a single task, so that more performance can be achieved in powerful hardware.
Designed for flash especially NOR Flash:
- much less erase times to extend flash life
- power safe, no middle-state status will exist
- key-value friendly usage, value supports binary format data
- minimum supported flash size is 8KB
To help device connect to cloud more easily, AliOS Things provide protocol stacks in flexible ways.
For IP oriented devices:
- a well-tested LwIP stack is provided for directly connected SoCs, including WiFi Soc, MCU+SDIO/SPI WiFi Module, etc.
- SAL(Socket Adapter Layer) for MCU attached with serial communication module such as WiFi/NB/GPRS.
- uMesh for building more complex, mesh networking topology
For non-IP devices:
- LoRaWAN stack is integrated
- BLE standard APIs, and BLE Stack
LoRaWAN and BLE Stack will be integrated in the near future.
AliOS Things maintains a TCP/IP stack based on LwIP v2.0.0, and support IPv4 Only, IPv6 Only, IPv4&IPv6 Coexist. IPv4 and IPv6 are well tested in daily CI. And IPv6 is widely used and tested in uMesh.
SAL is to provide standard Socket capabilities with serial WiFi/GPRS/NB-IoT modules. Specially, considering that AT Command is the most popular form in this scenario, a AT Parser is provided to help handling AT.
With SAL, developer can use common Socket APIs to access network, which will reduce integration efforts of existing software components.
uMesh is a mesh implementation with following features:
- RF standards independent, currently 802.11/802.15.4/BLE are supported, and more can be supported
- Routing mesh, support Tree Topology, Mesh Topology and Layered Tree&Mesh Topology
- Self-healing, no single point of failures
- Low Power Mode
- EAP(Extensible Authentication Protocol) with ID2
- Seamless IPv4/IPv6 integration providing Socket programming environment
Inherited from mbedtls, highly optimized for footprint.
Framework for accessing most of the security services such as ID2.
Trusted identity for Internet of things device.
Providing runtime Root of Trust through using security capabilities of hardware.
Providing classical algorithms implementation.
Providing total TEE soulution, C-Sky CK802T architecture are supported, ARMV8-M will be supported in the near feature.
FOTA (Firmware Over Tth Air) enables device firmware to update easily, AliOS Things provide customized FOTA solutions according to hardware configuration. Working with Alibaba Cloud services, AliOS Things provide a end-to-end solutions.
Features:
- supports rich IoT Protocols(Alink/MQTT/CoAP)
- support http/https/CoAP firmware download
- support multiple bin,delta and A/B update
- provide OTA HAL to make porting easily
uData is a specific software framework for IoT smart services based on a series of sensors, and has a general name of Sensor Hub traditionally.
There are two parts in the uData Framework. One is in the framework layer including uData service manager, service algo, abstact model(abs), and the other is in the kernel layer providing the sensor driver SDK.
The target scope of uData service will focus on the IoT business like drone toy, smart street lamp, sweeper robot and so on. The sensor drivers will not only provide the sensor SDK, but also provide sensor drivers like ALS, Barometer,temperature, accelerometer, gyro, magnetometer etc.
AliOS Things support rich cloud connection protocols:
- Alink: Alibaba Cloud Link platform, suitable for Smart Life. WiFi Provisioning component YWSS is also included.
- MQTT: standard MQTT protocol, well tested combining with Alibaba Cloud IoT Suite.
- CoAP: light weight UDP-based protocol. Together with CoAP FOTA, it is possible to build a UDP only system for like NB-IoT device.
AT Parser provides framework for handling AT commands with connected communication modules. AT Parser handles serial stream parsing, OOB callback could be registered to handle module special AT commands. Working with SAL, applications can use BSD sockets even on AT modules.
Implemented as a VS Code Plugin, providing edit/build/debug functionalities. Refer to AliOS-Things-Studio for more details.
Cooperating with AliOS Studio, it provides developers with a remote, and multiple devices debug environment. With the backbone Testbed framework, organizations can easily setup a CI based on real hardware.
AliOS Things is designed for low power, resource constrained MCU, connectivity SoC, greatly suitable for IoT devices.
For more detailed information, please go to : https://github.com/alibaba/AliOS-Things/wiki