Programming Embedded Systems, 2nd Edition

Using Flash Memory

Flash memory offers advantages over other types of memory. Systems with flash memory can be updated in the field to incorporate new features or bug fixes discovered after the product has been shipped. This can eliminate the need to ship the unit back to the manufacturer for software upgrades. There are several issues that need to be considered when upgrading software for units in the field.

Limit downtime

The timing of the upgrade should take place during downtime. Since the unit will probably not be able to function at its full capacity during the upgrade, you need to make sure that the unit is not performing a critical task. The customer will have to dictate the most convenient time.

Power failure

How will the unit recover should power be removed (intentionally or otherwise) while the upgrade is taking place? If only a few bytes of the application image have been programmed into flash when the power is removed, you need a way to determine that an error occurred and prevent that code from executing. A solution may be to include a loader (similar to a debug monitor) that cannot be erased because it resides in protected flash sectors. One of the boot tasks for the loader is to check the flash memory for a valid application image (i.e., for a valid checksum). If a valid image is not present, the loader needs to know how to get a valid image onto the board, via serial port, network, or some other means.

Another solution for power failures may be to include a flash memory ...