with the actual firmware from EspruinoBuilds the free area starts at 0x6c000 and ends at 0x7c000, @tve please correct me if I'm wrong
That is probably correct if it works for you ;-). The start really depends on where the current firmware binary ends. However, with the soon-to-happen change to a single firmware image for all flash chip sizes this is likely to change and may be different between flash chip sizes.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
That is probably correct if it works for you ;-). The start really depends on where the current firmware binary ends. However, with the soon-to-happen change to a single firmware image for all flash chip sizes this is likely to change and may be different between flash chip sizes.