[BUG] esp32c3 is missing support for legacy idf format

[Laczen]

Description / Steps to reproduce the issue

The esp32c3 (and probably other riscv-v based espressif devices) are missing support for the legacy (esp-idf) image format. The kconfig only allows selection of either the simpleboot format or the mcuboot format. Although a linker file is provided for the legacy format it is not possible to generate these kind of images.
There are several reasons to prefer the legacy image format over the simpleboot or the mcuboot format:

1. The generated images are smaller,
2. The generated images are position independent and can be started from any (only limited by the mmu alignment requirements).

On which OS does this issue occur?

[OS: Linux]

What is the version of your OS?

Ubuntu 24.04

NuttX Version

Master

Issue Architecture

[Arch: risc-v]

Issue Area

[Area: Build System]

Host information

No response

Verification

• I have verified before submitting the report.

[eren-terzioglu]

Hi,
We are not supporting IDF bootloader on newer implementation of esp32c3 and other risc-v devices (c6,h2,p4). Legacy C3, implementation, esp32/esp32s3 should have a support for that feature. It is not in our plans but if someone is planning to implement it, worth to take a look boards/xtensa/esp32s3/esp32s3-devkit/configs/knsh/defconfig file.

[Laczen]

@eren-terzioglu thank you for the feedback.

That is not good news, both the simpleboot and mcuboot format are by definition fixed location images as they include information about where they are running from. This disables any possibility for A/B images support (without the need to swap) for these devices. I can confirm that legacy-c3 supports it, but as far as I understood the intention is to drop this.

[tmedicci]

Hi @Laczen , just an additional note: the name of the Kconfig that enables it on ESP32-S3 is ESP32S3_APP_FORMAT_LEGACY. Deprecating its support and naming it as "legacy" was a design decision, not a bug: the IDF bootloader required a full ESP-IDF setup to build it. At that time, we didn't have other options: it was the first experiment we did to boot ESP32 devices on NuttX properly.

Simpler options were introduced, like the so-called simpleboot (direct bootloader) and MCUboot.

That being said, I highly recommend either closing this issue or renaming it as a feature request if you intend to keep supporting IDF bootloader for Xtensa and RISC-V ESP32 devices.

[Laczen]

Hi @eren-terzioglu and @tmedicci, after studying the boot process a bit further I found that it is possible to use the mcuboot format for location independent images. When the rom mapping is done by the bootloader they can be skipped in the NuttX image. But the image sizes cannot be as small as the legacy image sizes. This could also be done (in theory) for simpleboot images.

As there seem to be no further work is done for supporting the esp-idf bootloader it would be good to clearly mention this in the documentation.