Installing OpenBSD on the Pomera DM250 Writerdeck

This describes how to install OpenBSD-current on the Japanese-market Pomera DM250 / DM250X / DM250XY, along with a self-built custom kernel and U-Boot image distributed together. Since upstream support is not yet finished, the installation is experimental, and there are risks such as battery drain or boot failure. It explicitly states not to use this on the DM250US yet.

Before installing, it is recommended to take a full eMMC backup if possible. The device's factory recovery Linux is entered at power-on with Right Shift + Left Alt, and this recovery path runs /_sdboot.sh from the SD card to perform initial tasks. However, once a new U-Boot is written to eMMC, it will no longer be possible to boot into the factory Linux or recovery, so you need to plan a way to revert as well.

The SD card is prepared with a GPT + EFI partition + OpenBSD partition layout. The EFI partition contains BOOTARM.EFI, the provided uboot.img, and /_sdboot.sh. The OpenBSD partition contains the install sets from the latest armv7 snapshot, the bwfm firmware, and the bsd.rd and bsd kernels. This SD card serves as both the installation media and the recovery media.

The installation process is to insert the SD card, press Right Shift + Left Alt + Power to enter recovery, and let _sdboot.sh write the new U-Boot to eMMC. After that, the new U-Boot loads the OpenBSD bootloader via EFI, and boot> b bsd.rd runs the installer. When choosing the target disk, the eMMC is usually sd1, and the installation target should use whole disk so as not to overwrite the Rockchip ID block and the U-Boot start area.

During installation, the set files are read from the SD card, and the bwfm firmware is also installed automatically. After completion, since the installer tries to relink the kernel back to the upstream version, you need to copy the custom bsd from the SD card to /bsd on the installed system and disable /usr/libexec/reorder_kernel. Otherwise, the kernel may revert on the next boot.

After the first boot, an NVRAM file for bwfm is needed. Copying the firmware/nvram_ap6212a.txt backed up on the SD card to /etc/firmware/brcmfmac43430-sdio.rockchip,pomera-dm250.txt restores Wi-Fi to normal. If desired, you can change the U-Boot boot logo by placing logo.bmp at the root of the EFI partition, and you can also control the red/green LEDs by configuring GPIO in rc.securelevel.

Additionally, it explains how to build a custom bsd.rd. You extract the filesystem from the existing bsd.rd, build a RAMDISK kernel from the rk3128 tree, and then merge it back together with rdsetroot. This process must be done either by building directly on armv7 or by cross-compiling.

Recovery paths are also provided in case something goes wrong. If the eMMC is broken and even U-Boot won't boot, you can enter Rockchip loader / MaskROM mode, connect via USB cable, load RAM with xrock, and boot u-boot-ums.bin so the eMMC can be rewritten as if it were USB Mass Storage. If only the screen turns on and then hangs, U-Boot is still alive, and you can press a key to get the => prompt. In the worst case, you may need to open the device for UART access or to force entry into the eMMC.