Sercomm NA502

The Sercomm NA502 is a ZigBee/Z-Wave gateway sold under various brands (e.g. A1 Smart Home Gateway in Austria). It is based on the MediaTek MT7621 SoC with a Gigabit Ethernet port.

Important Some variants, like the Vera or Hornbach gateway, seem to have a crippled U-Boot that don't allow loading code to SDRAM via TFTP (password prompt when interrupting autoboot). The workaround for these devices is as follows:

1. Boot the device in download/recovery mode (keep reset button pressed on startup)
2. Use the sercomm-recovery utility to flash a dummy image; using the initramfs image has worked; this will not get the minimal system up and running, however, but it will seemingly corrupt the U-Boot parameters
3. After the flash, reboot the device, it will appear “bricked” and always try booting in download mode; press 2 in the U-Boot menu to load an image into flash via TFTP; you will again be prompted for a password, but you can simply press Enter to proceed, and now you can indeed configure the TFTP parameters; a full sysupgrade image can be loaded from here, booting via TFTP and loading the image into SDRAM and then upgrading with a sysupgrade image via the GUI has not worked, the device reverts to the initial initramfs after a reboot
4. When this process is done, you may need to adjust the U-Boot parameters manually so that it doesn't try booting via TFTP each time; choosing option 3 in the menu and using printenv to verify currently set parameters will reveal whether this is the case

Important: You need to attach a serial console to the unpopulated PIN header on the main PCB in order to install OpenWrt from U-Boot. There is a recovery mode, but the image format is currently unknown!

You need to attach a serial console to the unpopulated 4-pin header near the LEDs. With the front of the device facing towards you, the pinout is: GND - TXD - ? - RXD. The settings are 57600 8N1 and you should see a bunch of messages immediately after start.

• Using the terminal, select option 1. Load system code to SDRAM via TFTP.
• Put the initramfs OpenWrt image on your TFTP server and boot it.
• You can then use SSH to connect to the OpenWrt running from RAM.
• Transfer the OpenWrt squashfs image to the device (for instance to /tmp/openwrt.bin)
• Run sysupgrade -n /tmp/openwrt.bin to install the image to your device.

The device contains a recovery image in the first partition. If the device is brand new, connect it to the Internet so that it auto-updates the second image. Afterwards, the device boots always from image 2 as longs as its checksum is correct.

If you don't install a valid OEM firmware to image 2 first, the auto-update stored in image 1 overwrites OpenWrt right away.

There are Z-Wave and ZigBee modules. Both can be exposed using ser2net so that another gateway solution can connect to it.

• The Z-Wave module is at /dev/ttyS1 with 115200 8N1
• The ZigBee module is at /dev/ttyS2 with 57600 8N1

How to add tags