wolfBoot/IDE/pico-sdk/rp2350

wolfBoot port for rp2350 (Raspberry pi pico 2)

Support for TrustZone

By default, TZEN=1 is enabled in the provided configuration. wolfBoot will run from the Secure domain, and will stage the application in the Non-Secure domain.

The flash memory is divided as follows:

• wolfBoot partition (0x10000000 - 0x1003FFFF), 224 KB
• Non-secure callable partition (for secure gateway) (0x10038000 - 0x1003FFFF), 32 KB
• Boot partition (0x10040000 - 0x1007FFFF), 768 KB
• Update partition (0x10100000 - 0x1013FFFF), 768 KB
• Unused flash space (0x101C1000 - 0x101FFFFF), 252 KB
• Swap space (0x101C0000 - 0x101C0FFF), 4 KB

The SRAM bank0 is assigned to the Secure domain, and enforced using both SAU and ACCESS_CONTROL registers.

• Secure SRAM0-3: 0x20000000 - 0x2003FFFF, 256 KB
• Non-secure SRAM4-7: 0x20040000 - 0x2007FFFF, 256 KB
• Non-secure stack for application SRAM8-9: 0x20080000 - 0x20081FFF, 8 KB

Requirements

External debugger

As the two images (bootloader + application) are stored in different areas in the flash memory, a SWD connector is recommended to upload the binary images into the flash, as opposed to the default bootloader, allowing to upload non-signed applications into a storage device.

The scripts used in this example expect a JLink to be connected to the SWD port as documented here.

There is documentation below on how to do this with picotool instead, the scripts to error that it cannot file the JLink if you wish to use picotool instead, but this can be ignored.

PicoSDK

Clone the repository from raspberrypi's github:

git clone https://github.com/raspberrypi/pico-sdk.git

Export the PICO_SDK_PATH environment variable to point to the pico-sdk directory:

export PICO_SDK_PATH=/path/to/pico-sdk

Configuring wolfBoot to build with pico-sdk

From wolfBoot root directory, copy the example configuration:

cp config/examples/rp2350.config .config

You can now edit the .config file to change partition sizes/offsets, algorithms, disable trustzone, add/remove features, etc.

When TZEN=0, the application will run in the Secure domain.

When the configuration is complete, run make. This will:

• Build the key tools (keygen & sign):
• Generate the configuration header target.h
• Generate a new keypair (only once), and place the public key in the keystore

The environment has now been prepared to build and flash the two images (wolfBoot + test application).

Building and uploading wolfBoot.bin

After preparing the configuration and creating the keypair, return to the IDE/pico-sdk/rp2350/ directory and run:

cd wolfboot
export PICO_SDK_PATH=...
./build-wolfboot.sh

The script above will compile wolfboot as rp2350 second-stage bootloader. This version of wolfboot incorporates the .boot2 sequence needed to enable the QSPI device, provided by the pico-sdk and always embedded in all applications.

wolfboot.bin contains the bootloader, and can be loaded into the RP2350, starting at address 0x10000000. The script will automatically upload the binary if a JLink debugger is connected.

If you do not have a JLink you can install the binary using:

picotool load build/wolfboot.uf2

Building and uploading the application

cd ../test-app
./build-signed-app.sh

The script above will compile the test application and sign it with the wolfBoot private key. The signed application is then uploaded to the boot partition of the flash memory, at address 0x10040000.

The linker script included is modified to change the application entry point from 0x10000000 to 0x10040400, which is the start of the application code, taking into account the wolfBoot header size.

The application is signed with the wolfBoot private key, and the signature is stored in the manifest header of the application binary.

The output file build/blink_v1_signed.bin is automatically uploaded to the RP2350 if a JLink debugger is connected. The application image is stored in the boot partition, starting at address 0x10040000. The entry point of the application (0x10040400), set in the linker script hal/rp2350-app.ld, is the start of the application code, taking into account the wolfBoot header size.

To use picotool instead run:

picotool load build/blink_v1_signed.bin -o 0x10040000

Testing the application

The application is a simple blinky example, which toggles the LED on the board every 500ms.

If the above steps are successful, the LED on the board should start blinking.

The code has been tested on a Seeed studio XIAO RP2350 board and a Raspberry Pi Pico 2 (non-WiFi version).