Posted on May 17, 2011 at 14:29As ColdWeather points out your minimum blocking size for erase is the page size of the device you are using, nominally 1 or 2K.
Your finest write granularity is 16-bits (half word aligned).
With suitable de-blocking techniques you can write/replace anything you want. Just remember to do so smartly, so you maximize the amount of data being written, and minimize the erase cycles, limited as they are.
Also, be aware that writing to flash, while running from flash, will stall processor execution. Many flash devices don't even permit this, but on the STM32 you can, it will limit your ability to service the serial port in a timely manner, resulting in overruns. So don't write half-words as you received them, get a whole block, and use a method that uses flow-control techniques. Such a method would be XMODEM, it is a VERY simple protocol, but is extremely good for such tasks. ST has YMODEM examples, which isn't nearly as good because unless you can use CTS/RTS it is going to keep pushing a stream of data at you.
YMODEM is designed for error-correcting modems with hardware flow control. The ST implementation, last I looked, was a half assed cut-n-paste of some open source example on the web. The cut down version won't handle errors well, and basically assumes everything is going to work fine. Which is great when it does, but the real world isn't that kind.
Suggest also you down load the PM0042 document, which talks about flashing, and look at ST's serial flashing tools which include source and talk to the Boot Loader ROM.
