This HOW-TO will help you easily set up a PogoPlug to run NetBSD without needing to disassemble the device and solder on a serial adapter. When you're done, your PogoPlug will still be able to be booted into GNU/Linux but will automatically boot into NetBSD using the SD card slot as the root filesystem. 

You can choose to use a serial port, if you prefer. If you won't be using a serial port, skip the next part.

Pins on the PogoPlug (Mobile and Series 4) are numbered one through four immediately behind the SD card (where behind means towards the rear where the plugs are). One is farthest back and four is closest to the SD card slot. TxD is really transmit and RxD, receive. Connect at 115200 baud.

1: power (3.3 volts)
2: TxD
3: RxD
4: ground

If you're not using a serial connection, you'll have to create an account at http://my.pogoplug.com/, activate the device at https://my.pogoplug.com/activate/, then navigate to Settings (starting with the tiny gear icon in the top right of the web interface), select Security, then enable ssh for your PogoPlug. Choose your own ssh password. Then, ssh as user root to the IP of your PogoPlug.

Connect ethernet to a network where the PogoPlug can get a DHCP lease and access to the Internet. Either with a serial console or via ssh, you're at a root prompt. Paste in these lines to get tools and the NetBSD kernel.

cd /tmp
wget http://download.doozan.com/uboot/nandwrite
wget http://download.doozan.com/uboot/nandwrite
chmod +x nandwrite flash_erase
wget http://ftp.netbsd.org/pub/NetBSD/misc/jklos/netbsd.pogo.ub

If you like, you can get nanddump (via wget http://download.doozan.com/uboot/nanddump) and back up mtd3 before overwriting and scp it somewhere else. Something like this would work:

./nanddump -f pogov4mtd3.dump -o /dev/mtd3

Now we flash the actual NetBSD kernel. mtd3 is labeled "failsafe" in the mtd map and is 8 megs from the start of flash and 8 megs long. The block size on the PogoPlug is 131072 bytes, so 64 blocks of 128k each works out to 8 megs. The "-p" option of nandwrite is to pad the kernel to fit whole blocks.

Note that at this point we begin running commands which write to the internal flash. A mistake here could brick your PogoPlug, so proceed with caution!

./flash_erase /dev/mtd3 0 64
./nandwrite -p /dev/mtd3 netbsd.pogo.ub

Next, we write the environment variable bootcmd. Note that the mw commands in init_mmc are necessary so that NetBSD can use the SD card slot (many thanks to Lwazi for that). Enter the following as continuous lines (keep spaces where it wraps):

/usr/local/cloudengines/bin/blparam bootcmd='if ping 192.168.58.254; then run boot_nand; fi; run boot_bsd'
/usr/local/cloudengines/bin/blparam boot_bsd='run init_mmc; nand read.e 0x800000 0x800000 0x500000; bootm 0x800000'
/usr/local/cloudengines/bin/blparam init_mmc='mw f1010004 11113311; mw f1010008 551111'

For PogoPlug Pink, the beginning of mtd3 is 0x2500000, so use:

/usr/local/cloudengines/bin/blparam bootcmd='if ping 192.168.58.254; then run boot_nand; fi; nand read.e 0x800000 0x2500000 0x500000; bootm 0x800000'

Note that the kernel's current size is 4888832 bytes (but it may change, so please check), or 0x4a9900 in hex, so we can round up to 0x500000 in the nand read.e command like so. If you make a custom kernel, be sure to make sure the read.e command loads the entire kernel.

nand read.e 0x800000 0x800000 0x500000

We decide whether to boot NetBSD or GNU/Linux based on whether the PogoPlug can ping a machine on the local network. This gives us the option to flash a new kernel using GNU/Linux, if we like, without a serial console. In order to have the PogoPlug boot into GNU/Linux, create an IP alias at address 192.168.58.254 on any other machine on the same network. An example would be:

ifconfig usmsc0 inet 192.168.58.254 netmask 0xffffff00 alias

Once back in GNU/Linux, you can rerun the above but with a new kernel or your own custom kernel. Just copy and paste the wget of nandwrite and flash_erase, chmod them, wget or scp your own kernel, then flash_erase and nandwrite your kernel.

A sample kernel configuration file for NetBSD-current or NetBSD 7 is here:

http://ftp.netbsd.org/pub/NetBSD/misc/jklos/POGO

These notes can also be found here:

http://ftp.netbsd.org/pub/NetBSD/misc/jklos/pogoplug_notes

You can use another NetBSD machine to install NetBSD to an SD card and the kernel you just installed will use that as the root filesystem. A link for a quick NetBSD installation how-to will come soon.