# Flash the Radxa CM5 > Install the flashing tool, enter MaskROM mode, and write the image to the Radxa CM5. - Page: https://docs.menlo.ai/asimov/1/build/assembly-preparations/software-setup/flash-rpu - Section: Asimov › Asimov 1 › Assemble Asimov 1 › Preparation › Firmware & Software Flashing The Radxa CM5 (part `100_15X`) has no SD card slot. You flash its onboard storage over USB-C through the RPU, with the CM5 in a special MaskROM mode. ## Instructions 1. ### Install the Flashing Tool The tool differs by operating system. Windows uses a graphical tool; macOS and Linux use a command-line one. Open the section for your computer. > [!NOTE] > > **macOS and Linux: run the commands from your home folder** > > Before installing, run `cd ~` so the terminal is in your home folder. Running the install from a protected folder such as `~/Documents`, `~/Desktop` or `~/Downloads` can fail with a permission error. **Linux:** On Ubuntu 22.10 or newer, and current Debian: ```bash sudo apt install rkdeveloptool ``` On older distributions the package may not exist, in which case build it from source: ```bash sudo apt install -y libudev-dev libusb-1.0-0-dev dh-autoreconf pkg-config build-essential git git clone https://github.com/rockchip-linux/rkdeveloptool cd rkdeveloptool && autoreconf -i && ./configure && make -j"$(nproc)" sudo cp rkdeveloptool /usr/local/sbin/ ``` Check it worked: ```bash rkdeveloptool -V ``` No driver is needed. You will need `sudo` for the flashing commands. **macOS:** Install via Homebrew — no compiling required: ```bash brew tap IgorKha/rkdeveloptool brew install rkdeveloptool ``` If you encounter an untrusted tap error: ```text Error: Refusing to load formula igorkha/rkdeveloptool/rkdeveloptool from untrusted tap igorkha/rkdeveloptool ``` Fix it via the recovery instructions and run: ```bash brew trust igorkha/rkdeveloptool ``` Check it worked: ```bash rkdeveloptool -V ``` If the tap is unavailable, build from source instead: ```bash # We must use g++ on MacOS when building brew install automake autoconf libusb pkg-config gcc@15 # Clone and build git clone https://github.com/rockchip-linux/rkdeveloptool cd rkdeveloptool && autoreconf -i && CXX=/opt/homebrew/bin/g++-15 ./configure && make ``` **Windows:** Windows uses RKDevTool, a graphical tool, plus a USB driver. Both come from Radxa: 1. Download and extract DriverAssistant v5.14, then run `DriverInstall.exe` as administrator. Without this driver Windows will not recognise the board. 2. Download and extract [RKDevTool v2.96](https://dl.radxa.com/tools/windows/RKDevTool_Release_v2.96-20221121.rar), then launch `RKDevTool.exe`. 3. You will also need [7-Zip](https://www.7-zip.org/) to decompress the `.img.xz` image into a plain `.img` before flashing. The commands in [Write the Image](https://docs.menlo.ai/asimov/1/build/assembly-preparations/software-setup/flash-rpu.md#write-the-image) below are for macOS and Linux. For the RKDevTool click-through, follow [Radxa's RKDevTool guide](https://docs.radxa.com/en/som/cm/cm5/low-dev/rkdevtool-use) — with the board in [MaskROM mode](https://docs.menlo.ai/asimov/1/build/assembly-preparations/software-setup/flash-rpu.md#put-the-board-in-maskrom-mode) it will show “Found One MASKROM Device”, and you write the loader and image from there. If you have access to a Mac or Linux machine, we recommend using it — that is the path we test against. 2. ### Put the Board in MaskROM Mode ![RPU showing the USB-C connection, MaskROM button, and battery power connection order](https://docs.menlo.ai/manual/v1/images/firmware-flashing/rpu-maskrom.webp) Video: [Putting the RPU in MaskROM mode](https://static.asimov.inc/manual/v1/videos/rpu-maskrom-mode-97c08ad5f551.mp4) The order matters — the button must already be held down when the board first receives power. Connect power last. 1. Plug the USB-C cable provided from your laptop into the USB-C port on the RPU shown above. 2. Hold down the MaskROM button on the RPU. 3. While still holding it, press the on button on the battery to power the RPU. 4. Release the MaskROM button. 5. Confirm the laptop sees it: ```bash rkdeveloptool ld ``` You should see `Mode=Maskrom`. For example: ```text DevNo=1 Vid=0x2207,Pid=0x350b,LocationID=202 Maskrom ``` If the list is empty, re-seat the cable and repeat — the button must be held as the board is first powered, and the cable must carry data. 3. ### Write the Image The bootloader file `rk3588_spl_loader.bin` is the `rk3588_spl_loader_v1.15.113.bin` you downloaded in [Get the Images](https://docs.menlo.ai/asimov/1/build/assembly-preparations/software-setup.md#get-the-images) — rename it to match, or use its full name in the commands below. Writing takes a few minutes. **macOS and Linux:** ```bash rkdeveloptool db rk3588_spl_loader.bin # You should see: Downloading bootloader succeeded. xz -dk asimov-rpu-.img.xz rkdeveloptool wl 0 asimov-rpu-.img # The write process will begin. After a few minutes it will reach: # Write LBA from file (100%) rkdeveloptool rd # You should see: Reset Device OK. ``` On Linux these need `sudo`. The `xz -dk` line decompresses the image and keeps the original; the write itself needs the plain `.img`. **Windows:** In RKDevTool, with the board showing “Found One MASKROM Device”, load `rk3588_spl_loader.bin` as the loader and the decompressed `asimov-rpu-.img` as the image, then start the write. Step-by-step screens are in [Radxa's RKDevTool guide](https://docs.radxa.com/en/som/cm/cm5/low-dev/rkdevtool-use). Decompress the `.img.xz` with 7-Zip first — RKDevTool cannot read the compressed file. 4. ### Disconnect the RPU When it finishes, you should see an LED blinking blue on the RPU. You can now unplug the USB-C data cable and remove the battery power. **Previous:** [Get the Images](https://docs.menlo.ai/asimov/1/build/assembly-preparations/software-setup.md) · **Next:** [Flash the Raspberry Pi 5](https://docs.menlo.ai/asimov/1/build/assembly-preparations/software-setup/flash-raspberry-pi.md)