This only applies to NON-FOTA firmware versions. In order to flash ESP8266 the GPIO0 should be connected to GND. This is D3 on Wemos D1 Mini Pro.

The Espressif SDK family does not natively support a 16 MB flash mapping profile for application code execution. Instead, it handles a 16 MB chip (like the one on the WEMOS D1 Mini Pro) by addressing it as a 4 MB (32 Mbit) layout profile. The remaining 12 MB is invisible to the linker script and can only be accessed manually using raw sector reading/writing APIs (spi_flash_read).

In a traditional Non-OTA setup (referred to as eagle.flash.bin and eagle.irom0text.bin compiled via esp-open-sdk), the flash is mapped using Flash Map 4 (or 6 depending on the exact SDK version configuration).

Because it is targeted as a 4 MB envelope, the default critical system parameters are pushed to the very end of the first 4 MB segment, not the physical end of the 16 MB chip.

Your application compilation must use the correct linker script. Look inside your sdk directory (ld/) and ensure you target:

eagle.app.v6.ld

This forces the compiler to build the code assuming a single application image (Non-OTA) rather than splitting it into user1.bin and user2.bin layout profiles typical of an OTA environment.

When flashing an esp-open-sdk firmware onto the WEMOS D1 Mini Pro, you must be careful with the -fs (flash size) parameter. If you set -fs 16MB, the Espressif system configuration files will be expected at the absolute end of the 16MB space (0xFFC000), which will cause a boot loop (rf_cal_size error) because the SDK logic is expecting them at the 4MB mark.

To successfully flash a Non-OTA open-sdk project on this board, force a 4MB size parameter during upload:

esptool.py --port /dev/ttyUSB0 --baud 460800 write_flash \
 
  -fm dio -fs 4MB \
 
  0x00000 eagle.flash.bin \
 
  0x10000 eagle.irom0text.bin \
 
  0x3FC000 esp_init_data_default.bin \
 
  0x3FF000 blank.bin

Note: If you explicitly want to map out the hidden 12 MB for custom partition spaces or filesystems, you must flash esp_init_data_default.bin at 0xFFC000 and blank.bin at 0xFFF000, but you must manually ensure your custom open-sdk Makefile overrides the default FLASH_SIZE constants to prevent SDK crashes.

# Full erase first
esptool.py --port /dev/ttyUSB0 --baud 115200 erase_flash

# Flash esp-open-sdk/sdk/bin/esp_init_data_default.bin at 0x3fc000
esptool.py --port /dev/ttyUSB0 --baud 115200 write_flash 
               --flash_mode dio --flash_size 32m 
               0x00000 firmware/0x00000.bin 
               0x10000 firmware/0x10000.bin 
               0x3fc000 /home/oscar/esp8266/esp-open-sdk/sdk/bin/esp_init_data_default.bin

esptool.py --port /dev/ttyUSB0 --baud 115200 write_flash 
		--flash_mode qio --flash_size 32m 
                0x00000 firmware/0x00000.bin 
                0x10000 firmware/0x10000.bin

sudo python esptool/esptool.py erase_flash
sudo python esptool/esptool.py -p /dev/ttyUSB0 -b 460800 write_flash -fm qio 0x00000 0x00000.bin 

Finally got the Wemos D1 mini pro with 16 MByte flash.

esptool.py erase_flash
esptool.py -b 460800 write_flash -fm qio 0x00000 bin/0x00000.bin 0x10000 bin/0x10000.bin

And finally it was resolved with dev version of NodeMcu prepared in https://nodemcu-build.com/

My best result is 17 modules in the BIN. Many was unsuccessful I reported result in GitHub (with modules) - https://github.com/nodemcu/nodemcu-firmware/pull/1529

Also their own fixed esptool used - https://github.com/nodemcu/nodemcu-firmware/tree/dev/tools

• https://github.com/nodemcu/nodemcu-firmware/tree/dev
• http://nodemcu.readthedocs.io/en/dev/en/
• https://github.com/nodemcu/nodemcu-firmware/pull/1529
• https://nodemcu-build.com/stats.php
• http://tiestvangool.ghost.io/2016/08/13/flash-nodemcu-esp8266/
• http://www.letscontrolit.com/wiki/index.php/ESPEasy#Stable