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--- esp32_ota [2024/03/13 12:11]
sausage
+++ esp32_ota [2025/02/02 21:16] (current)
sausage CRC checksum details
@@ Line 5: / Line 5: @@
 Over The Air (OTA) provides a way to send firmware to your ESP32 board in the field without the need for a cable and physical access to the device.
-The purpose of this article is manually step through the various stages of the OTA process and illustrate the state of the ESP32 at each stage.
+The purpose of this article is to manually step through the various stages of the OTA process and illustrate the state of the ESP32 at each stage.
 Together we will set up a number of firmwares suitable for testing on different partitions in flash memory.
@@ Line 22: / Line 22: @@
 https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/ota.html#rollback-process
-This article is based on esp-idf-v5.1.1-2.
+This article is based on esp-idf-v5.2.
 ===== The stock firmware =====
@@ Line 35: / Line 35: @@
   gen_esp32part.py .\partitions.log > .\partitions.csv
+<WRAP center round important 90%>
+If you don't have gen_esp32part.py, please check the troubleshooter below.
+</WRAP>
 Open the CSV, and it will probably look something like this (if anything at all):
@@ Line 46: / Line 50: @@
 </code>
-Ignoring the ''nvs'' and ''phy_init'' partitions, we have the default ''factory'' partition that starts at 0x10000. Ironically, the list of partitions doesn't list the bootloader partition at 0x1000 or the partition that the partition table itself is stored on (at 0x8000).
+Ignoring the ''nvs'' and ''phy_init'' partitions, we have the default ''factory'' partition that starts at 0x10000. Ironically, the list of partitions doesn't list the bootloader partition at 0x1000 or the partition that the partition table itself is stored (at 0x8000).
 ===== OTA partitions =====
@@ Line 212: / Line 216: @@
   - 4blinks.bin
-Now the ''idf.py flash'' command is only able to flash the default project firmware to the ''factory'' partition. So we'll need to switch to a different command to flash a named firmware to a particular partition.
+Note that the ''idf.py flash'' command is only able to flash the default project firmware to the ''factory'' partition. So we'll need to switch to a different command to flash a named firmware to a particular partition.
 Take another look at our partitions table.
@@ Line 235: / Line 239: @@
   esptool.py -p COM7 write_flash 0x10000 .\build\3blinks.bin
-{{ :eso32:3blinks.jpg?direct&600 |}}
+{{ :esp32:3blinks.jpg?direct&600 |}}
   esptool.py -p COM7 write_flash 0x10000 .\build\4blinks.bin
-{{ :4esp32:blinks.jpg?direct&600 |}}
+{{ :esp32:4blinks.jpg?direct&600 |}}
 And put the 2blinks version back onto ''factory'' with:
@@ Line 280: / Line 284: @@
 This reads out the ''otadata'' partition, which starts at 0xd000 and is 0x2000 in length out to a file.
-If you open the ''otadata-partition.bin'' file in a hex reader (I recommend HxD - https://mh-nexus.de/en/hxd/), you'll see that the entire file is filled with 0xFF bytes.
+If you open the ''otadata-partition.bin'' file in a hex reader (I recommend [[https://mh-nexus.de/en/hxd/|HxD]]), you'll see that the entire file is filled with 0xFF bytes.
 We can use a tool to set ''ota_0''s firmware as the one we want to boot from:
@@ Line 286: / Line 290: @@
   otatool.py -p COM7 switch_ota_partition --name=ota_0
-{{ :eso32:3blinks.jpg?direct&600 |}}
+{{ :esp32:3blinks.jpg?direct&600 |}}
 The device will reset and notice that there are three LED blinks. This is the ''3blinks'' firmware running on ''ota_0''.
@@ Line 299: / Line 303: @@
 </code>
-Interesting. On the left is ''ota_0''. It has a boot sequence of ''01'' and a CRC check (not covered in this article). This partition will boot each time the ESP32 is reset. On the right is ''ota_1'', and there is nothing here to indicate if it should boot.
+Interesting. On the left is ''ota_0''. It has a boot sequence of ''01'' and a CRC checksum (keep a note of this, we will come back to this). This partition will boot each time the ESP32 is reset. On the right is ''ota_1'', and there is nothing here to indicate if it should boot.
 We can also verify the ''otadata'' partition and take a closer look at what is stored there now.
@@ Line 315: / Line 319: @@
 ''9A 98 43 47'' is the firmware checksum.
+Remember the CRC checksum in ''ota_0''?
+''0x4743989a''. This is how you can confirm which firmware is running.
 Let's switch to booting the firmware on ''ota_1'':
@@ Line 322: / Line 330: @@
 The ESP32 will reboot and the LED will begin blinking 4 times. This is the ''4blinks'' firmware booted on the ''ota_1'' partition.
-{{ :4esp32:blinks.jpg?direct&600 |}}
+{{ :esp32:4blinks.jpg?direct&600 |}}
 Take a look at the ''otadata'' information again:
@@ Line 354: / Line 362: @@
 In our case, the second sector has a new entry, the ''02'' sequence. This is for the firmware on ''ota_1''. ''02'' is greater than ''01'' so this is the firmware selected for boot by the bootloader.
+Again we can inspect the checksum: ''0x55f63774'' is ''74 37 F6 55''.
+How an OTA partition is determined from sequence numbers in the otadata partition is not explained in the documentation, but is explained in the code. You can see it here: https://github.com/pycom/esp-idf-2.0/blob/master/components/app_update/esp_ota_ops.c#L297
+Essentially, for two partitions all odd sequence numbers are ''ota_0'' and even numbers are ''ota_1''. The formula is:
+  (ota_seq - 1) % number_of_ota_partitions
 Revise on the ''otadata'' partition here:
@@ Line 387: / Line 403: @@
   esptool.py -p COM7 write_flash 0xd000 .\otadata-partition.bin
-{{ :4esp32:blinks.jpg?direct&600 |}}
+{{ :esp32:4blinks.jpg?direct&600 |}}
 The device will reset and the ''4blinks'' firmware is still running on the ESP32 from the ''otadata'' partition.
@@ Line 410: / Line 426: @@
 Let's see. All we need to do is to reset the ESP32. Press the reset button.
-{{ :eso32:3blinks.jpg?direct&600 |}}
+{{ :esp32:3blinks.jpg?direct&600 |}}
 Wow, notice something? The ''3blinks'' firmware from ''ota_0'' has been booted. Let's extract the otadata again and take a look what has occurred:
@@ Line 439: / Line 455: @@
   esptool.py -p COM7 write_flash 0xd000 .\otadata-partition.bin
-{{ :eso32:3blinks.jpg?direct&600 |}}
+{{ :esp32:3blinks.jpg?direct&600 |}}
 The ESP32 will reset and ''3blinks'' firmware continues to execute. Let's take a look at the raw ''otadata'' again:
@@ Line 460: / Line 476: @@
 All our firmwares failed to run the ''esp_ota_mark_app_valid_cancel_rollback()'' to mark the ''otadata'' as valid. So in each case, they have become aborted and rolled back to the previously known good firmware.
-The ''factory'' firmware isn't controlled by the ''otadata'', the rollback process or OTA at all.
+The ''factory'' firmware isn't affected by ''otadata'', or the rollback process, or OTA at all.
 To finish up, let's take a last look at the raw otadata:
@@ Line 486: / Line 502: @@
 Have fun!
+===== Troubleshooting =====
+//The gen_esp32part.py command isn't found.//
+For some reason, gen_esp32part.py is not added to your path by default when starting your ESP-IDF console. For Powershell add the following to line 59 of your ''frameworks\esp-idf-v5.2\export.ps1'' file:
+  function gen_esp32part.py { &python "$IDF_PATH\components\partition_table\gen_esp32part.py" $args }
+For Windows Command Prompt, in ''frameworks\esp-idf-v5.2\export.bat'' add to line 66:
+  DOSKEY gen_esp32part.py=python.exe "%IDF_PATH%\components\partition_table\gen_esp32part.py" $*
+For shell and fish terminals, it's the same deal.
 ===== More reading =====
   - https://blog.espressif.com/ota-updates-framework-ab5438e30c12
   - https://esp32.com/viewtopic.php?t=14939
+===== Thank yous =====
+Many thanks to boarchuz and craig from the [[https://discord.gg/wwK29JJV|Espressif MCUs]] discord server for their assistance with this article.

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