# UTAT Device Firmware Upgrade with MCUboot

Documentation of the steps taken to implement MCUBoot for Device Firmware Upgrades.

## Environnment config
Use the environment written in flake.nix by running `nix develop`


## Set up Zephyr
Zephyr is the RTOS that uses the MCUboot bootloader being set up.

[Getting started with Zephyr](https://docs.zephyrproject.org/latest/develop/getting_started/index.html)

```sh
west init zephyrproject
cd zepyhrproject
west update

west zephyr-export

cd zepyhr
west sdk install
```

## MCUBoot POC Implementation

MCUBoot is a bootloader for Zephyr, which allows multiple firmwares to exist on a board. MCUBoot can dynamically switch which firmware is active. This is useful in the event of one firmware failing.

[Abstract MCUBoot Guide](https://docs.mcuboot.com/readme-zephyr.html)



## Configure partition sizes

The devicetree specification file declares the hardware configuration. The flash storage needs three partitions, one for boot, and two for the two firmwares it will hold.

[DeviceTree Specification documentation](https://docs.zephyrproject.org/latest/build/dts/intro-scope-purpose.html)

[Partitioning examples](https://docs.zephyrproject.org/latest/build/dts/api/bindings/mtd/fixed-partitions.html)

The board I'm using has its DeviceTree Specification in `zephyr/boards/st/nucleo_g431rb/nucleo_g431rb.dts`

I created a partition for MCUBoot, two firmware slots, and additional storage in the flash storage.

```c
&flash0 {
	partitions {
		#address-cells = <1>;
		#size-cells = <1>;
		ranges;

		boot_partition: partition@0 {
			compatible = "zephyr,mapped-partition";
			label = "mcuboot";
			reg = <0x00000000 0x0000C000>;
		};

		slot0_partition: partition@C000 {
			compatible = "zephyr,mapped-partition";
			label = "image-0";
			reg = <0x0000C000 0x0000A000>;
		};

		slot1_partition: partition@14000 {
			compatible = "zephyr,mapped-partition";
			label = "image-1";
			reg = <0x00016000 0x0000A000>;
		};
	};
};
```

(Originally my partitions were 8000B each but MCUBoot would not build as its boot partition was too small. By using direct-xip there is no need for additional storage for copying images either.)


## Enable building for MCUboot with direct-xip
Add these lines to `bootloader/mcuboot/boot/zephyr/prj.conf`

```sh
### Must be enabled to build applications for MCUboot
CONFIG_BOOTLOADER_MCUBOOT=y
### Allows in-place execution
CONFIG_BOOT_DIRECT_XIP=y
### Allows switching the image
CONFIG_BOOT_DIRECT_XIP_REVERT=y
```

Then in `zephyr/samples/basic/blinky/prj.conf` and `zephyr/samples/basic/blinkyslow/prj.conf` add the following:
```sh
CONFIG_BOOTLOADER_MCUBOOT=y
CONFIG_IMG_MANAGER=y
CONFIG_FLASH=y
CONFIG_REBOOT=y
```

## Enable switching firmware
Each time a peice of firmware is run, set the other one as the upgrade so it runs next time. Add this to the code early in main:

```c
#include <zephyr/dfu/mcuboot.h>
#include <zephyr/sys/reboot.h>

int main() {
	/* Confirm ourselves so MCUboot doesn't revert us on a later reset */
	if (!boot_is_img_confirmed()) {
		boot_write_img_confirmed();
	}

	/* Arm a permanent swap so the other image runs after the next reset */
	boot_request_upgrade(BOOT_UPGRADE_PERMANENT);
	...
}
```

Also, create an overlay for the firmware being executed in place. This is so the code jumps to addresses in the right block. Create `zephyr/samples/basic/blinkyslow/boards/nucleo_g431rb.overlay`

```
/ {
	chosen {
		zephyr,code-partition = &slot1_partition;
	};
};
```




## Set up crypto
```sh
python bootloader/mcuboot/scripts/imgtool.py keygen -k private.pem -t rsa-2048

openssl rsa -in private.pem -pubout > public.pem
```




## Build the firmware

```sh
west build -p always -b nucleo_g431rb -d build_mcuboot bootloader/mcuboot/boot/zephyr --

west build -p always -b nucleo_g431rb -d build_fast zephyr/samples/basic/blinky

west build -p always -b nucleo_g431rb -d build_slow zephyr/samples/basic/blinkyslow
```


## Sign the firmware
```sh
python bootloader/mcuboot/scripts/imgtool.py sign \
    --key private.pem \
    --header-size 0x200 \
    --pad-header \
    --align 8 \
	--pad \
    --version 1.2 \
    --slot-size 0xA000 \
    build_fast/zephyr/zephyr.bin \
    blinky-signed.bin

python bootloader/mcuboot/scripts/imgtool.py sign \
    --key private.pem \
    --header-size 0x200 \
    --pad-header \
    --align 8 \
	--pad \
    --version 1.2 \
    --slot-size 0xA000 \
    build_slow/zephyr/zephyr.bin \
    blinkyslow-signed.bin
```

## Flash the firmware

`su root` allows flashing to usb devices, run  `nix develop` again if using it.

`flash0@0x08000000` in `zephyr/dts/arm/st/g4/stm32g4.dtsi`
```sh
pyocd flash -t stm32g431rbtx build_mcuboot/zephyr/zephyr.hex
pyocd flash -t stm32g431rbtx --base-address 0x0800C000 blinky-signed.bin
pyocd flash -t stm32g431rbtx --base-address 0x08016000 blinkyslow-signed.bin
```