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 # Adafruit nRF52840 Bootloader
 
 This repository contains the USB bootloader for Adafruit nRF52840 boards (1MB flash, 256KB SRAM).
+This repository depend on the  [tinyusb](https://github.com/hathach/tinyusb/tree/develop) as submodule, after cloing this repo you need to run this command
+
+    git submodule update --init
+
+## Build with makefile
+
+Navigate to `src/singlebank` (recommended) or `src/dualbank` (work in progress), and use feather52840 target for building bootloader.
+
+	make feather52840
+
+To flash bootloader + S140
+
+	make flash_feather52840
+    
+To only flash S140
+
+	make flash_sd
+
+## Build using Segger Embeded Studio
+
+For better debugging you can also use SES, The project file is located at `src/segger/nrf52840_bootloader.emProject`.  Note: the SES only flash the bootloader when you click download, you need to flash Softdevice beforehand if you haven't done so ( use `make flash_sd` mentioned above )
+