simmel-bootloader/README.md

# Adafruit Bluefruit nRF52 Bootloader

This is a CDC/DFU/UF2 bootloader for nRF52 boards.

- [Adafruit Feather nRF52832](https://www.adafruit.com/product/3406)
- [Adafruit Feather nRF52840 Express](https://www.adafruit.com/product/4062)
- Nordic nRF52840DK PCA10056
- Nordic nRF52840DK PCA10059 ("Dongle")
- Particle Argon
- Particle Boron
- Particle Xenon

UF2 is an easy-to-use bootloader that appears as a flash drive. You can just copy `.uf2`-format
application images to the flash drive to load new firmware.
See https://github.com/Microsoft/uf2 and https://github.com/adafruit/uf2-samdx1
for more information.

[adafruit-nrfutil](https://github.com/adafruit/Adafruit_nRF52_nrfutil),
a modified version of [Nordic nrfutil](https://github.com/NordicSemiconductor/pc-nrfutil),
is required to perform DFU.
Install `python3` if it is not installed already and run this command to install adafruit-nrfutil from PyPi:

```
$ pip3 install --user adafruit-nrfutil
```

This repository depends on the following submodules:

- [tinyusb](https://github.com/hathach/tinyusb/tree/develop)
- [nrfx](https://github.com/NordicSemiconductor/nrfx)

Note that `tinyusb` also includes `nrfx` as a submodule, so you need
to initialize and update  submodules with the `--recursive`` flag.

Clone this repo with following commands, or fork it for your own development

```
git clone https://github.com/adafruit/Adafruit_nRF52_Bootloader
cd Adafruit_nRF52_Bootloader
git submodule update --init --recursive
```

## Features

- DFU over Serial and OTA ( application, Bootloader+SD )
- Self-upgradable via Serial and OTA
- DFU using UF2 (https://github.com/Microsoft/uf2) (application only)
- Auto-enter DFU briefly on startup for DTR auto-reset trick (832 only)

## How to use

There are two pins, `DFU` and `FRST` that bootloader will check upon reset/power:

- `Double Reset` Reset twice within 500 ms will enter DFU with UF2 and CDC support (only works with nRF52840)
- `DFU = LOW` and `FRST = HIGH`: Enter bootloader with UF2 and CDC support
- `DFU = LOW` and `FRST = LOW`: Enter bootloader with OTA, to upgrade with a mobile application such as Nordic nrfConnect/Toolbox
- `DFU = HIGH and `FRST = LOW`: Factory Reset mode: erase firmware application and its data
- `DFU = HIGH and `FRST = HIGH`: Go to application code if it is present, otherwise enter DFU with UF2
- The `GPREGRET` register can also be set to force the bootloader can enter any of above modes (plus a CDC-only mode for Arduino).
`GPREGRET` is set by the application before performing a soft reset.

On the Nordic PCA10056 DK board, `DFU` is connected to **Button1**, and `FRST` is connected to **Button2**.
So holding down **Button1** while clicking **RESET** will put the board into USB bootloader mode, with UF2 and CDC support.
Holding down **Button2** while clicking **RESET** will put the board into OTA (over-the-air) bootloader mode.

On the Nordic PCA10059 Dongle board, `DFU` is connected to the white button.
`FRST` is connected to pin 1.10. Ground it to pull `FRST` low, as if you had pushed an `FRST`  button.
There is an adjacent ground pad.

For other boards, please check the board definition for details.

## Burn & Upgrade with pre-built binaries

You can burn and/or upgrade the bootloader with either a J-link or DFU (serial) to a specific pre-built binary version
without the hassle of installing a toolchain and compiling the code.
This is preferred if you are not developing/customizing the bootloader.
Pre-builtin binaries are available on GitHub [releases](https://github.com/adafruit/Adafruit_nRF52_Bootloader/releases)

Note: The bootloader can be downgraded. Since the binary release is a merged version of
of both bootloader and the Nordic SoftDevice, you can freely upgrade/downgrade to any version you like.

## How to compile and build

You should only continue if you are looking to develop bootloader for your own.
You must have have  a J-Link available to "unbrick" your device.

### Option 1: Build with Makefile

Prerequisites

- ARM GCC
- Nordic's [nRF5x Command Line Tools](http://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.tools%2Fdita%2Ftools%2Fnrf5x_command_line_tools%2Fnrf5x_installation.html)

To build:

```
make BOARD=feather_nrf52840_express all combinehex
```

To flash the bootloader:

```
make BOARD=feather_nrf52840_express flash
```

To flash SoftDevice (and chip erase):

```
make BOARD=feather_nrf52840_express sd
```

To erase all of flash:

```
make BOARD=feather_nrf52840_express erase
```

For the list of supported boards, run `make` without `BOARD=` :

```
$ make
You must provide a BOARD parameter with 'BOARD='
Supported boards are: feather_nrf52840_express feather_nrf52840_express pca10056
Makefile:90: *** BOARD not defined.  Stop
```

### Common makefile problems

#### 1. `arm-none-eabi-gcc`: No such file or directory

If you get the following error ...

```
$ make BOARD=feather_nrf52840_express all 
Compiling file: main.c
/bin/sh: /usr/bin/arm-none-eabi-gcc: No such file or directory
make: *** [_build/main.o] Error 127
```

... you may need to edit the `Makefile` and update `GNU_INSTALL_ROOT` to point to the root path of your GCC ARM toolchain.

#### 2. `mergehex: No such file or directory`

Make sure that `mergehex` is available from the command-line. This binary is
part of Nordic's nRF5x Command Line Tools.

#### 3. `make: nrfjprog: No such file or directory`

Make sure that `nrfjprog` is available from the command-line. This binary is
part of Nordic's nRF5x Command Line Tools.

On POSIX-type systems you can temporarily add the path to `nrfjprog` via a
variation on the following command:

```
$ export PATH=$PATH:/location/of/nRF5x-Command-Line-Tools_9_7_2_OSX/nrfjprog
```

### Option 2: Build using Segger Embedded Studio

For easier debugging you can also use [SES](https://www.segger.com/products/development-tools/embedded-studio/).
The project file is located at `src/segger/Adafruit_nRF52_Bootloader.emProject`.

> **Note**: SES only flashes the bootloader when you click download, not the SoftDevice.
You need to flash the SoftDevice beforehand if you haven't already done so.
As mentioned above do something like:

```
make BOARD=feather_nrf52840_express sd
```