I stand corrected! Thanks, good to know the caching issue exists on 5.1.
Regarding updating bootloader: on the bottom of the pcb there are 5 pads that run to the debug interface of the CC2540. It would be possible to for a user to update firmware through that interface, but the calibration data is also written in the flash memory and may have to be wiped. I can’t remember off the top of my head if the CC2540 lets you change the flash page locks without a full chip erase. The other factor is that the code necessary to read from SD is actually pretty large, including it in the bootloader image may requine reducing the space for the application image, which means changing the flash map, which means all previous versions of firmware become incompatible with the new bootloader.
In short I really like the idea of loading firmware from SD, but it’s got some challenges associated that could quickly become a support nightmare, so I need to think about the tradeoff some more.
Are you an EE using the CC2540? The firmware isn’t open source but I’m happy to answer questions about it.