STM32F1 Flash Memory Module

This is a module (STM32F1Flash (About Modules)) for reading and writing internal flash memory on the STM32F103RC chip in the Espruino Board.

THIS IS DEPRECATED - There is now built-in support for writing flash memory of all STM32 boards, available via the Flash module


Flash memory contains Espruino, your saved program, and the bootloader - and it's almost all used. Incorrect use of this module could stop your Espruino board from working, so make sure you know what you're doing!


  • Flash memory must be erased (so it is all 0xFF) before it is written to. If you don't do this you could damage it.
  • While you can write individual 32 bit words to flash, it must be erased in blocks of 2048 bytes.
  • Flash memory starts at 0x08000000
  • The Espruino board has 256kB of Flash memory (or you can check with process.memory().flash_length)
  • Bytes 0x08000000 to 0x08002800 are the bootloader. Doing ANYTHING with these will almost certainly break your board permanently (requiring a re-flash using a USB-TTL convertor).
  • From 0x08002800 to process.memory().flash_binary_end is Espruino (usually around 200kB - but this will increase in the future). Overwriting this will require a re-flash of your board via the bootloader
  • From process.memory().flash_code_start to 0x08000000+256kB is used for your saved program
  • This means that between 0x08000000 + sizeof(your_espruino_binary_file.bin) and 0x08000000+256kB-40kB is free for your use - roughly 16kB.

Figuring out what memory is free

process.memory() returns information on the addresses of various things on the device. For instance you can see how much spare memory there is by calling process.memory().flash_code_start - process.memory().flash_binary_end. To find the first page that you can safely erase, you can type:


It's also good practice to check if there's anything in the page of flash. If it's all 0xFF (4 bytes of 0xFF is 0xFFFFFFFF, which is bitwise equivalent to -1) then you're safe to overwrite it:

function isPageSafe(addr) {
  for (var i=addr;i<addr+2048;i+=4)
    if (peek32(i)^-1) return false;
  return true;

// returns true - it's all fine

isPageSafe(((process.memory().flash_binary_end+2047)&~2047) - 2048)
// returns false - don't use this address!
var adr = 0x0803E000;
var f = require("STM32F1Flash");
console.log(; // probably FFFFFFFF
f.unlock(); // unlock flash memory - allows us to do bad things...
f.erase(adr); // erase 2048 bytes from 0x0803E000
console.log(; // now definitely FFFFFFFF
f.write(adr,0xCAFEBABE); // write a 32 bit word
console.log(; // now CAFEBABE

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