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POSIX in the age of IoT: Benefits and limitations

Posted: 14 Jul 2014     Print Version  Bookmark and Share

Keywords:POSIX  API  operating systems  Linux  microprocessors 

With a large number of devices, specialised communications protocols, power consumption and memory footprint become very important. The bulk of these devices will be medium sized MCU based devices, likely mostly in the ARM Cortex M class of machines: big enough to communicate through the Internet using full security protocols, but small enough to be really inexpensive and low power.

In IoT, one of the key features is wireless communication. Many wireless protocols and many wireless gateways will be supported Wide area wireless (GPRS, 3G, LTE) and short range wireless will be offered with integrated gateways (Bluetooth 4.0, WiFi, 6loWPAN, Zigbee IP, Zigbee Pro, UHF, 802.15.4). Wireline access to the cloud will be provided for data storage and analytics. Figure 4 compares the network data rate and range of some of the protocols.

Figure 4: The figure shows the basic trade off of bandwith versus distance for various protocols. Wide areas are served with 2G/GPRS, 3G and LTE while WiFi, Bluetooth 4.0, Zigbee Pro, Zigbee IP, 6loWPAN, UHF and 802.15.4 serve more local needs.

Other IOT requirements include:
 • Memory footprint is critical, one size does not fit all. Some applications require a very tiny low power part while others require more processing and more memory.
 • To achieve a small memory footprint, unnecessary features need to be removed and at the highest level module level modularity is a key feature to accomplish this.
 • Optimisation of each component or module for feature set minimisation are required.
 • Optimisation options for each component to minimise size are required
 • Security is key, but it must be integrated at the design of components, be space optimised to trade off security requirements versus space requirements, and use the current set of accepted best practice ('practise' when verb)s standards.
 • Safety is important but this safety must be tailorable to the application in question.
 • Complex technologies like virtualisation are not required, these devices to not need this level of complexity.
 • Technologies like multi-core are rarely needed and would typically be used in larger gateways and routers to move data into the cloud.
 • Discontinuous and continuous operation are required depending on the application

The complexity, time to market, requirements and development costs for these IoT devices make MCUs or small MPUs with an RTOS an ideal choice. Note that embedded Linux won't run in these environments.

Developers can get to market quickly with minimal cost with exceptional functionality using off the shelf POSIX compliant RTOS solutions. And by taking care in the choice of MCU RTOSes with regard to POSIX , a developer can achieve some of the benefits associated with a full Linux implementation, particularly software reuse and training, It maximises software reuse and training while minimising memory footprint size, time to market and also supports lean product development.

The Internet of Things and POSIX
Larger IoT gateways and devices can use the combination of existing POSIX APIs and the emerging IoT protocols. This may include standard Internet protocols and higher level protocols which offer various publish subscribe features and/or data transmission protocols for big data collection.

Various wireless connections can also be supported using the standard POSIX APIs. These large nodes might use larger multi-core MPUs, Linux or larger embedded operating systems and virtual memory.

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