rBoot and OTA updates


rBoot is an open source bootloader for the ESP8266, which is now fully integrated with Sming. rBoot is a more flexible alternative to the closed source bootloader supplied by Espressif with the SDK. A bootloader allows you to have more than one application on the esp8266, either completely different apps, or different version of the same app, which can be updated over the air.

The example Basic rBoot demonstrates the use of rBoot, but if you want to add it to an existing project this little tutorial will guide you.

Need to know

  • The esp8266 can only memory map 1MB of flash at a time, your ROM must fit within the a single 1MB block of flash.
  • Different 1MB blocks can be mapped at different times, so your ROM does not have to be within the first 1MB block. The support for this in rBoot is called big flash mode. A single compiled and linked ROM image can be placed at the same relative position in any 1MB block of flash.
  • If you have two smaller ROMs in a single 1MB of flash (your only option if you flash is 1MB or smaller) this is referred to as two ROM mode in rBoot. Each ROM needs to be separately linked to have the correct memory mapped flash offset. Examples are given below for common scenarios.


  • The default rBoot options are perfect for a 4MB flash, so if this is what you have (e.g. an esp-12) you don’t need to do anything else. Otherwise see information below about configuration.
  • Run make as normal, rBoot and your app ROM will both be built for you.
  • Running make flash will flash rBoot and the first ROM slot.

Configuring for two ROM mode

If you have a 1MB flash, you will need to have two 512KB ROM slots, both in the same 1MB block of flash. Set the following options in your project’s component.mk file:

RBOOT_ROM1_ADDR = 0x80000
SPI_SIZE        = 1M


To use SPIFFS think about where you want your SPIFFS to sit on the flash.

If you have a 4MB flash the default position is for the first ROM to be placed in the first 1MB block and the second ROM to be placed in the third 1MB block of flash. This leaves a whole 1MB spare after each ROM in which you can put your SPIFFS.

If you have to a smaller flash the SPIFFS will have to share the 1MB block with the ROM. For example, the first part of each 1MB block may contain the ROM, and the second part the SPIFFS (but does not have to be split equally in half). So for the 4MB example you could put the SPIFFS for your first ROM at flash address at 0x100000 and the SPIFFS for your second ROM at 0x300000; in each case that is the 1MB block after the ROM.

To mount your SPIFFS at boot time add the following code to init:

int slot = rboot_get_current_rom();
uint32_t address = (slot == 0) ? RBOOT_SPIFFS_0 : RBOOT_SPIFFS_1;
//debugf("trying to mount SPIFFS at %x, length %d", address, SPIFF_SIZE);
spiffs_mount_manual(address, SPIFF_SIZE);

Over-the-air (OTA) updates

Instead of insisting on a “one-solution-fits-all” approach, Sming provides you with the ingredients to build an OTA upgrade mechanism tailored to your application. This involves selecting a transport protocol and a backend that interacts with the flash memory. Any protocol from Sming’s rich set of network classes can be used, ranging from raw TCP sockets to HTTP, FTP, MQTT, with or without SSL, etc. To conserve program memory, you might prefer a protocol already employed by your application.

On the backend side, there is OtaUpgradeStream from the Over-the-Air Firmware Upgrade library, which supports multiple ROM images in one upgrade file, as well as state-of-the-art security features like a digital signatures and encryption. Check out the HttpServer Firmware Upload example, which demonstrates a browser-based firmware upgrade mechanism similar to what is found in many consumer products.

A more lightweight solution is provided by RbootOutputStream, which is just a thin wrapper around rBoot’s flash API, in combination with RbootHttpUpdater, which pulls individual ROM image from an HTTP server. Add the following code:

RbootHttpUpdater* otaUpdater = nullptr;

void OtaUpdate_CallBack(RbootHttpUpdater& client, bool result)
    if (result) {
        // success - switch slot
        uint8_t slot = rboot_get_current_rom();
        if (slot == 0) {
            slot = 1;
        } else {
            slot = 0;
        // set to boot new ROM and then reboot
        Serial.printf("Firmware updated, rebooting to ROM %d...\r\n", slot);
    } else {
        // fail
        Serial.println("Firmware update failed!");

void OtaUpdate()
    // need a clean object, otherwise if run before and failed will not run again
    delete otaUpdater;
    otaUpdater = new RbootHttpUpdater();

    // select ROM slot to flash
    rboot_config bootconf = rboot_get_config();
    uint8_t slot = bootconf.current_rom;
    if (slot == 0) {
        slot = 1;
    } else {
        slot = 0;

    // flash ROM to position indicated in the rBoot config ROM table
    otaUpdater->addItem(bootconf.roms[slot], ROM_0_URL);
    // flash appropriate ROM
    otaUpdater->addItem(bootconf.roms[slot], (slot == 0) ? ROM_0_URL : ROM_1_URL);

    // use user supplied values (defaults for 4MB flash in makefile)
    otaUpdater->addItem((slot == 0) ? RBOOT_SPIFFS_0 : RBOOT_SPIFFS_1, SPIFFS_URL);

    // set a callback

    // start update

You will need to define ROM_0_URL, ROM_1_URL and SPIFFS_URL with http urls for the files to download.