Sure. I have no docs I can release of that, but very quickly: The ESP31 has three regions of RAM: an IRAM for the first cpu at 0x40040000 (which is 128K), an IRAM for the second CPU at 0x3ffa8000 (64K) and a shared RAM at 0x3FFD8000 (192K). The IRAMs actually are 32K bigger than that, but if SPI ...

finally got the board run.
with the example running there is 78324 bytes ram left.

#include "esp_common.h"

/******************************************************************************
* FunctionName : user_init
* Description : entry of user application, init user function here
* Parameters ...

Ok, solved.
same as esp8266, pull gpio0 to low.

How to enter flash programming mode? any specs doc?
Pull GPIOx low/high?
what tool is used to flash the chip?