SDK v3

[eriksl]

I noted when switching to the current v3 SDK:

- user_rf_pre_init is NO LONGER called (contrary what is said above). You can set a variable in your function and check it later to see.
- user_rf_cal_sector_set is NO LONGER called (contrary what is said above). You can set a variable in your function and check it later to see.
IRAM space has shrinked considerately, I lost about 450 bytes.
- "heap free" has increased by 16k. I suspect the "use IRAM for DRAM" function is enabled by default (contrary to the documentation), let's see how we switch that off, it would be nice to have a function to check IRAM usage

Instead of using IRAM for DRAM, I'd rather use IRAM flash cache for IRAM flash code (i.e. the 32 k part that is always almost full because SDK code uses most of it).

Which half of the IRAM cache space is being used for DRAM if enabled? Upper or lower?

[Her Majesty]

Ask on GitHub may be a better choice, engineers are more active there. https://github.com/espressif/ESP8266_RTOS_SDK