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The “Short Blanket” Effect – Engineering Challenges in Implementing FOTABy Sharon Peleg Founder and CTO Red Bend Software Updating mobile firmware is not a simple task. Some have compared it to updating software on a PC, but there are in fact many engineering challenges that make updating mobile firmware much more difficult. While the generator running on a PC in the office can practically enjoy no resource limitations, the design of the update process on mobile devices must take into account the lack of any auxiliary data, lack of extra storage to be used as temporary buffers, lack of RAM in some cases and a much weaker CPU. Ineffective approaches could easily lead to conflicts between the various resources, and result in the “short blanket” effect – if you pull it from one side, the other side is left uncovered. When evaluating, testing and integrating FOTA on mobile devices, manufacturers and operators should consider the following: · Speed, accuracy and predictability of update generation · No spare flash memory on the device · Fault tolerance · Size of the delta file and update package · Positive user experience · Updating compressed firmware · Type of flash memory In this blog entry, I will address the first three. Speed, Accuracy and Predictability of Update Generation The update algorithm must be fast enough to generate updates at a reasonable speed and should provide sufficient feedback to allow proper understanding of the behavior of the update process on the device. Another equally important requirement is the need for the update generation to be predictable. It is not only sufficient that the generator will produce a small update when few changes are introduced to the source, it must do so consistently. No Spare Flash Memory on the Device The fact that there is no spare flash memory for building two side-by-side alternating versions when updating the new version (as some embedded devices can afford to have) leaves no option but to perform an update in-place. In-place delta-updating is challenged by limited spare flash and RAM resources to hold the new version. Fault Tolerance When updating firmware on mobile devices, it is crucial to assume that the process could be interrupted at any point in time due to a power failure. Power failure during flash re-programming not only can corrupt the written flash sector but also leave the device in a useless state. In addition to having to be both in-place and fault-tolerant, the process must run at maximum speed to minimize downtime. Fault tolerance requires writing additional data when updating in order to maintain the integrity of the persistent data at any point in time. The challenge here is to minimize writing data in order to minimize the number of re-flash operations. Learn more about implementing FOTA in our new white paper, “Principles of Updating Mobile Firmware Over-the-Air”. Labels: FOTA, mobile, software
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