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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 

Unison and POSIX. Unison's initial release in 1987 used POSIX compliant interfaces and by 1993 offered POSIX conformant interfaces for I/O and full compliance by 1995 for standard I/O and multi-threading. New releases in 2007 focused on MCUs and MPUs, providing modular and tiny optimised versions for PSE51 and PSE52 plus additional networking support. today, Unison 5.2.3 offers a wide set of POSIX APIs for a single process, multi-threaded environment with I/O (PSE52) with many networking and memory protection features from PSE53 as well as a shell and other features from PSE54.

Porting a Linux app to a POSIX RTOS. With 100% POSIX, porting can be fast and easy. Standard API's don't require changing unless the existing application includes depreciated features or uses features that are not supported. In most POSIX RTOS offerings, dealing with problems of size, multiple processes and signals are the main issues.

To deal with size problems, rewrite and restructure to eliminate large buffers, provide more processing intensive algorithms which save memory ( for example a hashing scheme rather than a sparse matrix ) and exploit modularity and optimisation features of the RTOS. Compile time options can also be used to minimise size.

To adapt to a world without multiple processes is more difficult and may require significant work to start threads instead of processes and communicate effectively. It is all doable within a few weeks for almost all applications with the time being application dependent. Signals can also be eliminated and this requires minor changes to replace signals with other POSIX calls.

Figure 8: Esight's Intelligent Eyewear is helping blind people see.

Figure 8:

Example #1: Intelligent eyewear

Shown in figure 8 is an intelligent eyewear example. In this case, an existing Linux application existed for MPU based hardware. The goal was to port this application to the Unison OS for a variety of reasons including:
 • Elimination of the high cost of Linux maintenance was a primary goal. Unison comes with supported releases.
 • Elimination of the high complexity of Linux drivers and driver variants was also a primary goal. Unison comes with off the shelf drivers and is easily understood and enhanced with a small fraction of the complexity of Linux. Unison also has service offerings for driver augmentation and troubleshooting.
 • Zero boot time was a nice to have, but not a driving factor.

The basic port took two person days to port the multi-threaded application. Enhancements and optimisations took another two person weeks.

Example #2: Wearable device analysis
Consider the case of building a new wearable clothing device. One option is to implement an Android wearable. This requires an MPU and the smallest option is something similar to an Arm Cortex A9. In this case we get the following results:
 • BOM Cost—$40 (volume dependent)
 • Power Consumption – very high
 • Physical Size – large
 • Weight – heavy (large battery)

An alternative implementation would use the Unison OS and an Arm Cortex M3 class machine.
 • BOM Cost—$20 (volume dependent>
 • Power Consumption – low
 • Physical Size – interim size using smt medium, using BGA – tiny
 • Weight – light (small battery)

The second alternative offers all the software features along with significantly less expensive hardware. Unison OS has WiFi and Bluetooth for connectivity, a range of IoT protocols for discontinous operation and the ability to easily and quickly integrate a broad set of sensors. The development time is less than three months using this approach.

Conclusion
POSIX is the leading set of operating system APIs and work well on embedded IoT devices. By providing these standard APIs, time to market and total cost of ownership are minimised. Software reuse is also maximised, significant rework is eliminated in many cases and training is eliminated.

For the Internet of Things (IoT), POSIX RTOS offerings for MCUs and MPUs are ideal. They significantly reduce time to market and total cost of ownership while matching technical requires such as small memory footprint, modularity, optimisation, wireless support and other requirements very well.

Unison OS is an MCU and MPU RTOS for IoT which has all the necessary features to port applications from larger POSIX operating systems, embedded Linux or larger POSIX RTOS offerings quickly and easily. Unison also fully supports new development with a full range of IoT features for MCU and MPU development.

About the author
Kim Rowe is the founder of RoweBots, which offers the Unison RTOS along with complete one-stop product development of Internet of Things systems to OEM developers targeting the Internet of Everything. Kim has 30+ years of experience in systems engineering and holds both an MBA and an MEng.Unison OS is an MCU and MPU RTOS for IoT which has all the necessary features to port applications from larger POSIX operating systems, embedded Linux or larger POSIX RTOS offerings quickly and easily. Unison also fully supports new development with a full range of IoT features for MCU and MPU development.

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