The Open AT operating system is the heart of Wavecom’s family of wireless solutions.
It elevates Wavecom products above being simple bit-pipe modems to become sophisticated and powerful computing platforms. It provides users not only with core embedded realtime programming capability, but also the capability to connect to globally standardised cellular wireless networks.
As the Open AT realtime operating system (RTOS) natively supports wireless functionality, it provides guaranteed response time to external and hardware timer interrupts – not only when the GSM stack is idle, but regardless of the operating state the wireless CPU is in – IDLE, voice call, GPRS transfer etc. It is a pre-emptive multitask RTOS which uses semaphores to synchronise tasks, and allows customer tasks to have higher priority than non-critical GSM stack tasks.
The software suite – which comprises an OS, IDE, plug-ins and firmware elements – has been created specifically to meet the demanding requirements of the M2M industry and has evolved to serve automotive and mobile professional segment needs. Applications are written in standard C and run natively on top of the RTOS, with a minimum memory footprint and processor resource overhead.
The operating system
In Wavecom’s wireless CPU, two different binaries are embedded and smoothly executed at the same time – each one being protected from the other by a memory access protection feature.
The first binary, called the firmware, provides the wireless functionality. It is Wavecom-owned property that has been fully developed and tested to provide stability impressive enough that some customers have licensed it from Wavecom.
The second binary is the customer’s product-specific software and is based on an application development layer that brings an extensive set of high level APIs (application programming interfaces). With it, users can develop and execute applications in standard ANSI-C. These applications use core features of the Open AT OS such as realtime operations and seamless access to all hardware resources such as buses, GPIOs, memory, power saving modes, interrupts and hardware timers.
Wavecom guarantees that whatever GSM state the wireless CPU is in, it takes no longer than one millisecond to start code execution related to external interruption or hardware-timer interruption.
Plug-ins provided with the software development kit are also available to use as Open AT libraries. These provide an opportunity to use and integrate field-proven, advanced features such as IP networking in application code, without having to develop them.
Embedded software architecture
Guaranteeing realtime capabilities to any hosted application while simultaneously certifying that any wireless operation will be conducted successfully is not an easy task. It not only requires complete know-how of the GSM protocols, but also full ownership of the code as well as full control over the wireless CPU on which this feat must be accomplished.
In the Open AT architecture, Application Tasks are the core of the customer application. This component is designed to execute high level processes that are not time critical.
The Interrupt Task has been designed to perform ‘long’ or resource demanding operations such as complex calculations or value acquisition report creation and storage in Flash memory. These operations are performed asynchronously and are not time critical.
This Interrupt Handler is the second highest priority process on the platform. It is designed to perform asynchronous time critical operations. Its code will start being executed within less than 1 millisecond upon interruption (HW timer or external) detection. It is designed to perform very short operations such as value acquisition and storage in RAM (for instance in a circular buffer).
To ensure that the code is properly executed on the wireless CPU, Wavecom provides watchdogs to independently monitor any application executed on the CPU.
For more information contact Gyula Wendler, Arrow Altech Distribution, +27 (0)11 923 9600, [email protected], www.arrow.altech.co.za
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