Application prints random symbols and restarts

First try setting the baud rate to 74880. Example for Linux:

python -m serial.tools.miniterm /dev/ttyUSB0 74880

The random symbols should become readable messages.

If you see repeating messages containing rf_cal[0] !=0x05 then most probably you should initialize the flash memory on your ESP8266 device.

To achieve this do the following:

1. Set the SPI_SIZE of your flash memory. Example: If you have device with 4 megabytes make sure that the following is set:

export SPI_SIZE=4M

2. Run flashinit.

Run the following commands.

cd $SMING_HOME/../samples/Basic_Blink
make flashinit

flashinit is erasing the current flash memory and populating some areas on it with the bytes that your SDK / BootROM is expecting to be present.

This command needs to be executed only when you change SDKs or memory layouts.