HCC Embedded has developed a specialised filesystem for smart meters designed to reduce power consumption and increase flash memory lifetime by removing much of the overhead associated with general-purpose filesystems.
Based on a structured database, the HCC Smart-meter File System (SMFS) requires less than 15kbyte of program memory and less than 1.5kbyte of RAM on most 32bit MCUs.
“We designed this very closely with one of the world’s biggest meter manufacturers,” said David Brook, director of sales and marketing at HCC. “Our objective was to lower system cost and increase reliability by taking a data-centric approach rather than file-based. Record structures in most smart meters are well-defined and don’t change much. By designing a filesystem around that, the number of times that you have to erase and rewrite the flash are dramatically reduced.”
Dave Hughes, CEO of HCC said that using a standard filesystem meant that to write a record to flash would involve a number of operations that are not necessary in such a restricted application. To hide the need to erase and rewrite data in blocks, a flash translation layer (FTL) is usually needed on top of which software deploys a conventional filesystem. “Then, normally, you have to create your filesystem on top of that.”
Hughes said the SMFS offers a more streamlined approach than a standard filesystem. “It offers a reduction in power consumption and an increase in lifetime of the flash. We can simulate use cases with the customer and see how long the flash will last.”
The filesystem has been written using the MISRA C:2004 guidelines, Hughes said, and in such a way that guards against problems caused by unexpected resets. “The system guarantees the integrity of the data itself. Everything is done in a failsafe way to ensure that the filesystem can never be corrupted. We’ve dealt for years in failsafe and reliable systems. This is our sixth filesystem and most of them involve failsafes. People don’t want to lose their data. It’s a real pain if you have something on the bottom of the North Sea and you bring it up and find that the data isn’t there.”