Supporting direct boot bare metal applications (no esp-idf)

[MabezDev]

It's great that espflash has support for existing idf applications/bootloaders/partition tables; however in recent chips there is support for the direct boot feature (read more here: https://github.com/espressif/esp32c3-direct-boot-example) which espflash currently does not support.

To fix this the following functionality should be able to be toggled on/off based on the type of application:

• Using the FirmwareImage format, direct boot won't work with this format we should instead just flash the loadable sections as is.
• flashing the partition table
• flashing the 2nd stage bootloader

Perhaps the toggle could simply be --format idf|raw defaulting to one or the other.

[igrr]

One note, the esp binary image format currently implemented in espflash might also change somewhat depending on the chip. For example, esp8266 ROM uses a slightly different image header compared to ESP32 series ROM. ESP8266 RTOS SDK bootloader uses yet another image header format. Future chips might have same header formats but different padding requirements (e.g. 16kB instead of 64kB).

For this reason I think it would be good to think of format selection as an enum rather than an on/off toggle, even if only two options are implemented initially.

[mchodzikiewicz]

Hi, I have made some work on this without noticing this issue:
https://github.com/mchodzikiewicz/espflash/pull/1/files

The result I have is that the binary is very similar to one created by objcopy, but the section that should start at 0x0 (.text I guess) is located at 0x00010000, did not have time to investigate why yet

On the branch above there is a small hack that dumps binary created from ELF to the bin file., I used this to diff between objcopy of an ELF file and container with a binary that is ready to be flashed by espflash. Repo I tried this on was https://github.com/MabezDev/esp32c3-experiments

I expect this to be the last problem to have it working for the ESP32C3.

[icewind1991]

also #58 did some rework towards this goal