Flash memory has been the storage technology of choice for embedded Linux from the beginning and over the years Linux has gained very good support, from low-level drivers up to flash-aware filesystems, the latest being UBIFS.

However, as the rate at which new flash technologies are introduced increases, it is becoming harder to keep pace with the changes at the high end. System designers are increasingly turning to managed flash in the form of eMMC to provide a stable hardware and software interface which is independent of the memory chips inside. Embedded Linux developers are beginning to get to grips with these new chips. Support for TRIM in ext4 and F2FS is well established, and it is slowly finding its way into the chips themselves. Also, the appearance of new filesystems that are optimized to manage flash, such as F2FS, is a welcome step forward.

However, the fact remains that flash memory is not the same as a hard disk drive. You have to be careful to minimize the number of filesystem writes – especially as the higher density TLC chips may be able to support as few as 1,000 erase cycles.

Finally, it is essential to have a strategy for updating the files and images stored on the device in the field. A crucial part of this is the decision to use a package manager or not. A package manager gives you flexibility, but cannot give you a fully Murphy proof update solution. Your choice depends on the balance between convenience and robustness.

The next chapter describes how you control the hardware components of your system through the use of device drivers, both in the conventional sense of drivers that are part of the kernel, and also the extent to which you can control hardware from the user space.