Random Integers Crash Embedded Swift with ESP-IDF 5.2.2 and 5.3.1 for ESP32-C6

Paul Solt -

As of 9-12-2024, Random integers are not usable with Embedded Swift with a release version of ESP-IDF.

There is an open issue on the Swift Embedded Examples github, which requires a workaround patch to get it build.

If you attempt to use random numbers, you'll see a panic and your ESP32 will keep restarting forever with the crashing code.

let z = Int.random(in: 0...25) // !!!!!!!!!!!!!!!!!!!! RANDOM Number CRASHES Embedded Swift!

Your crash stack frame may look like:

panic_abort (details=details@entry=0x4081195c "abort() was called at PC 0x42006459 on core 0") at /Users/paulsolt/esp/esp-idf/components/esp_system/panic.c:466

...

#8  arc4random_buf (buf=0x40811a38, n=8) at /builds/idf/crosstool-NG/.build/HOST-x86_64-apple-darwin21.1/riscv32-esp-elf/src/newlib/newlib/libc/stdlib/arc4random.c:214
#9  0x4200e45c in $sSGsE4next10upperBoundqd__qd___ts17FixedWidthIntegerRd__SURd__lFs27SystemRandomNumberGeneratorV_SuTg5 ()

If you are using ESP-IDF 5.2.2 or 5.3.1 or earlier, there's an issue with the ESP-IDF build tools that needs a patch.

Note: You may be able to use the master branch without patching, but that may be less stable than a fixed version that is known to work with Embedded Swift.

Apply a Patch for ESP IDF 5.2.2

One of the developers from Espressify posted the patch files. I have only modified them so that they can work for version 5.2.2 and 5.3.1 which I had installed.

  1. Download the patch you need to fix random numbers
    2. ESP-IDF 5.2.2 Random Number Patch
    3. ESP-IDF 5.3.1 Random Number Patch

Apply the patch (5.2.2 or 5.3.1)

git apply ~/Dowloads/esp32c6_random_crash_fix_5.2.2.patch

Navigate to your ESP build folder

cd ~/esp/esp-idf/

Now you should be all set, but you can try using the latest from master or a future release to fix this issue.

How to Update Your Install of ESP-IDF

If you want to try a different version or master you can follow these steps to see if that will fix the problem without the need for a workaround patch.

This can take a minute or two depending on your connection speed.

cd ~/esp/esp-idf

git fetch --all --tags --prune

Checkout the latest version (5.3.1 as of 9/12/2024):

git checkout v5.3.1

git submodule update --init --recursive

Now you need to install the latest changes from ~/esp/esp-idf:

./install.sh

After that you need to do a full clean in your project folder and build again.

Cross your fingers and hopefully it works, otherwise checkout the version like Apple's guide recommended.

# Navigate to your project folder
idf.py fullclean
idf.py build
idf.py flash monitor

Let me know if this helped you. You can find me on X: @PaulSolt