Is it possible to download the firmware attached to the email and update the ESP32 itself?

[rtek1000]

One of the difficulties in carrying out OTA via the Internet is the redirection of router ports. Or complex storage servers are used.

Since ESP32 firmwares are generally not very large (below 10MB), would it be possible to use this library to perform OTA via email?

[rtek1000]

Related: #311

[mobizt]

It was already implemented in this example and the topic you mentioned.

The only requirement is you have to send your Email with that bin file as attachment via the standard mail client app or using this library to send Email.

This is to make sure that the attachment size property was properly set in the message header.

This attachment size will be used to calculate the firmware size for proper flash space preparation.

[rtek1000]

I followed the steps described, and the ESP32 was able to log in and update, but I would like more guidance, please:

• IMAP is configured to delete the message (send it to the trash, which must wait 30 days to permanently delete it). But it is necessary for the IMAP client to delete the message.
• • I found the sketch that deletes the message, but how do I delete only the message that was read with "firmware.bin"?

The idea of deleting the message is to prevent an infinite update loop from occurring, as the idea is that the updated firmware can also update itself.

---

Another thing is the issue of the firmware sent accidentally having a BUG and then not being able to perform the next update.

• So I thought about using an ESP32 to just serve as an updater for another ESP32.

Since it is possible for the ESP32 update to be done via the serial port, can you provide an example in this way?

[rtek1000]

Another thing is the issue of the firmware sent accidentally having a BUG and then not being able to perform the next update.

* So I thought about using an ESP32 to just serve as an updater for another ESP32.

Since it is possible for the ESP32 update to be done via the serial port, can you provide an example in this way?

I found this esp-serial-flasher , it seems possible.

[mobizt]

The update will not happen automatically that causes infinite loop updating unless this condition met.
imap_data.firmware_update.attach_filename = "firmware.bin";

And you have to search for unseen or new email and set that message as seen before fetching with those UIDs or sequence numbers.
https://github.com/mobizt/ESP-Mail-Client/blob/master/examples/IMAP/Search_And_Read/Search_And_Read.ino

It is easy for you to manage this with your code to change the option imap_data.firmware_update.attach_filename based on file version revision e.g. firmware_v1.0.0.bin instead of using the same file name as firmware.bin.

Any firmware update over other mechanisms of Email is out of library scope and you have to done it with your code.

[mobizt]

For delete, you have to use search too.

Note that, you can do anything after OTA update before you restart your device e.g. search and delete messages.

[rtek1000]

Another thing is the issue of the firmware sent accidentally having a BUG and then not being able to perform the next update.

* So I thought about using an ESP32 to just serve as an updater for another ESP32.

Since it is possible for the ESP32 update to be done via the serial port, can you provide an example in this way?

I found this esp-serial-flasher , it seems possible.

I noticed that it was not necessary to use the SD card to update via email.

Is the SD card necessary if an ESP32 programs another ESP32 via UART?

In the example code it appears that the SD card is used:

Overview

Example demonstrates how to flash ESP32/ESP32-S2/ESP8266 from another (host) MCU using esp_serial_flash component API. In this case, ESP32 is also used as host MCU. Binaries to be flashed from host MCU to another Espressif SoC can be found in binaries folder and are converted into C-array during build process.

Following steps are performed in order to re-program target's memory:

Filesystem is initialized and mounted.
UART1 through which new binary will be transfered is initialized.
Host puts slave device into boot mode tries to connect by calling esp_loader_connect().
Binary file is opened and its size is acquired, as it has to be known before flashing.
Then esp_loader_flash_start() is called to enter flashing mode and erase amount of memory to be flashed.
esp_loader_flash_write() function is called repeatedly until the whole binary image is transfered.

Note: In addition, to steps mentioned above, esp_loader_change_transmission_rate is called after connection is established in order to increase flashing speed. This does not apply for ESP8266, as its bootloader does not support this command. However, ESP8266 is capable of detecting baud rate during connection phase, and can be changed before calling esp_loader_connect, if necessary.

https://github.com/espressif/esp-serial-flasher/tree/master/examples/esp32_example

[mobizt]

For OTA, it is done on-the-fly with chunks data and the filesystems (SD and Flash) are not needed.

The one of SD or flash filesystem was used in IMAP examples for the messages and attachments download which the OTA case is different and was not require filesystem for download.

[mobizt]

You can remove SD_Card_Mounting(); from your code in case firmware file saving was disabled.

ESP-Mail-Client/examples/IMAP/Firmware_Update_Attachment/Firmware_Update_Attachment.ino

Lines 197 to 198 in 5c6e231

	/* save (download) firmware to file? */
	imap_data.firmware_update.save_to_file = false;