Generating bootloader for specific device?

[yanshay]

I want to use esp-web-tools to flash my application, and for some reasons I need to flash the bootloader separately from other parts. So I need to prepare a bootloader image file.
I'm using esp32s3.
I found here bootloader for esp32s3, but I learnt that I need to modify it a bit based on the SPI flash mode and Flash Size (https://docs.espressif.com/projects/esptool/en/latest/esp32s3/advanced-topics/firmware-image-format.html#file-header).

I did that manually and then had two issues:

1. This bootloader crash chrome browser after the flashing (using esp-web-tools) is done (even though it seems like flashing went ok, because connecting to the device shows logs and app is running)
2. In the boot logs I saw the bootloader stating MD5 SHA issues.
   So I thought maybe the 2nd issue is causing the 1st one.
   Therefore, I'm trying to figure out if there's a way to create a bootloader image that fit my device with all settings and SHA and maybe other things. I know I can create an image for the entire application and bootloader and partition table, but couldn't find how to do generate only a bootloader image.

Also, in case this doesn't eventually solve the 1st issue, any ideas what could cause esp-web-tools not to work well with this bootloader (to the level of crashing chrome browser)? Are there different types of bootloaders and maybe the one used in the rust world is not compatible with the one assumed by esp-web-tools (which underneath use esptools-js)?

[jessebraham]

I don't know what esp-web-tools is, but we do not provide support for software we do not develop. I think this should be pretty obvious.

The bootloader is provided by ESP-IDF, you can find the relevant information in their documentation.

[bjoernQ]

You probably want to ask about esp-web-tools at: https://github.com/esphome/esp-web-tools

As Jesse said - we are using the ESP-IDF bootloader which should be well supported by esp-web-tools. If not that's a bug in esp-web-tools

[yanshay]

Thanks

You probably want to ask about esp-web-tools at: https://github.com/esphome/esp-web-tools

I plan to ask there after I have a bootloader that I know is good. The current one that I managed to generate complains in the logs as if the SHA is wrong.

My question was really about this project, the rest was just to provide some context - is there a way using espflash to generate just a bootloader (not the entire app image) after it's modified with the flash size, the SPI Flash mode, SHA and anything else that I might be missing. Since when I did it myself in other ways it didn't end up with a valid bootloader.

[bjoernQ]

Not sure I understand what you did - so you manually patched the bootloader flash-mode in the binary?

That's not going to work - you need to build the bootloader from source with the correct settings - a different flash mode will compile different code via conditional compilation. Easiest is to build an esp-idf hello-world example and you will get the bootloader binary.

For the SHA mismatch - if you manually change some bytes, you also need to recalculate the SHA

In any case first test your bootloader by flashing with espflash or esptool - if everything works fine move on to 3rd party tools like esp-web-tools

[yanshay]

Not sure I understand what you did - so you manually patched the bootloader flash-mode in the binary?

Yes. I took the esp32s3 bootloader from this repo and manually modified these two bytes(2nd and 3rd). When flashed (also with espflash or esptool.py, don’t remember which I tried as well as esp-web-tool) to address 0x0000, along with the bin of the partition table and then the app (as three separate chunks to different addresses), the application worked only the bootloader complained on sha.
I think this is what espflash does as well with those binaries here. I tried following the code but couldn’t tell for sure.

But could be that some parts of the bootloader that are important for esp-web-tools needs are wrong which cause some failure (though crashing chrome means some bug in chrome as well and surely shouldn’t happen no matter what).

I will try as you suggested getting a bootloader without these manual tweaking.

BTW - this approach of flashing from the browser is pretty common, not something unique I‘m doing. The only thing less common I think is that I am flashing it in parts and not as a single binary, maybe I’ll need to change that.

[yanshay]

To summarize my finding related to this issue in case it helps anyone in the future:

1. I found a workaround to get esp-web-tools to work, it seems like they have some bug which for some reason occurs much more with esp-idf bootloaders.
2. The easiest way to generate a bootloader for esp-hal I documented in How to create a bootloader to flash not using espflash? #712 (comment) (seems like I asked it some time ago, today I thought if the trivial answer really)
3. When pursuing the esp-idf approach to create a bootloader, I found that espflash is using a much older version of esp-idf bootloader and I couldn't get a valid up-to-date esp-idf bootloader to work. I documented my tests in esp-hal binaries (partition-table/application) don't seem to be compatible to new version of esp-idf bootloader. esp-hal#2983 but closed the issue after I no longer need this, but in case anyone is interested it's there.

Thanks