The functions of the `esp*/freetos` libraries must be placed in IRAM because they can be called when the IROM cache is disabled. While the functions implemented in `cpu/esp8266/freetos/*.c` are already placed in IRAM, the functions implemented in `cpu/esp_common/freetos/*.c` are not placed in IRAM. The reason for this is that the object files of these files are created in the `esp_freertos_common` directory, which is not included in the `esp.riot-os.ld` file because the library is named `esp_freertos_common`.
RIOT-OS uses part of Espressif ESP8266 RTOS SDK to build support for
this CPU. The SDK includes some vendor-provided closed source
pre-compiled libraries that we need to modify to adapt to RIOT-OS
usage. This library modifications was done once and uploaded to a fork
of the vendor repository and was provided as an environment variable.
This patch changes two things:
1. It installs the SDK as a RIOT PKG from the new pkg/esp8266_sdk
directory instead of requiring the user to download it separately.
2. It performs the library modifications (symbol renames) on the pkg
Makefile removing the need to use a fork with the modifications applied
and simplifying the SDK update and future modifications.
This change sets the SDK package version (git SHA) to the same one that
our fork was using as a parent in the vendor repository, meaning that
the output libraries are exactly the same as before.
Tested with
```
ESP8266_RTOS_SDK_DIR=/dev/null USEMODULE=esp_log_startup make -C tests/shell BOARD=esp8266-esp-12x flash
```
and verified that the program works. The boot message now includes:
```
ESP8266-RTOS-SDK Version v3.1-51-g913a06a9
```
confirming the SDK version used.
`/dev/null` in the test is just to make sure that no evaluation of
`ESP8266_RTOS_SDK_DIR` in make is affected by the environment variable
value which would be set to the SDK for people who followed the set up
instructions before this change.
Tested the checkout size:
```bash
$ du -hs build/pkg/esp8266_sdk/
124M build/pkg/esp8266_sdk/
```
Checksumming flash is not supported on xtensa platform:
Warn : not implemented yet
make: *** [.../RIOT/examples/saul/../../Makefile.include:796: flash] Error 1
https://github.com/espressif/openocd-esp32 is needed.
Example config (when compiled from source):
export OPENOCD="~/esp/openocd-esp32/src/openocd -s ~/esp/openocd-esp32/tcl"
The xfa.ld script is incompatible with binutils > 2.35.2 and results
in firmwares that wont boot. Sadly, I couldn't figure out an elegant
way to fix the issue. Instead, I modified the linker script provided
by binutils to also include XFA.
