Escape

Batman — Wi-Fi HaLow mesh on Raspberry Pi 4

Field notes from getting a Morse Micro MM6108 Wi-Fi HaLow (802.11ah) radio working over SPI on a Raspberry Pi 4, and building it into a batman-adv mesh node.

Hardware: Raspberry Pi 4 Model B + Seeed WM1302 Pi HAT + Seeed Wio-WM6108 mPCIe card (Quectel FGH100M-H / Morse Micro MM6108A1).

TL;DR — the finding

The Morse Micro morse_spi driver fails to probe on a stock Raspberry Pi OS kernel:

morse_spi spi0.0: failed to init SPI with CMD63 (ret:-71)

The driver's SPI init sequence must send 144 training clocks with chip-select deasserted. It does that by temporarily setting SPI_CS_HIGH to invert CS polarity.

On kernels ≥ 6.1 with GPIO-descriptor chip-selects (cs-gpios, which the Pi 4 base device tree always uses), the SPI core sets SPI_CS_HIGH itself and handles polarity through the GPIO descriptor flags. The driver's |= SPI_CS_HIGH therefore becomes a no-op, and the training clocks go out with CS asserted. The chip counts them as real bus traffic and its bit counter ends up exactly 2 bits out of phase for the rest of the session.

Fix: use SPI_NO_CS instead, so the core skips CS toggling entirely and the pin stays high during training. → patches/0001-spi-use-SPI_NO_CS-for-training-sequence.patch

This is only needed because stock Raspberry Pi OS does not carry Morse Micro's kernel patch (the one that defines SPI_CONTROLLER_ENABLE_CS_GPIOD). Their own OpenWrt / MorseMicro/rpi-linux builds do.

Three things were required, all necessary:

1. Driver from the MM6108 product line — tag mm6108-2.0.1, not mm8108-*
2. The SPI_NO_CS patch above
3. Module parameters enable_ext_xtal_init=1 bcf=bcf_fgh100mhaamd.bin

Result:

morse_spi spi0.0: Loaded firmware from morse/mm6108.bin, size 468304, crc32 0xbe7b5c8f
morse_spi spi0.0: Loaded BCF from morse/bcf_fgh100mhaamd.bin, size 1251, crc32 0x941b2a82

Then: the shortcut we should have found first

After all of the above, the driver worked — but a HaLow link still could not be established, because Debian's stock wpa_supplicant (v2.10) contains zero S1G / 802.11ah support, and hostapd / morse_cli were not present at all.

It turns out OpenMANET publishes a prebuilt OpenWrt image for exactly this hardware combination — it lists "Seeed WM1302 + Wio-WM6108" as a supported SPI setup, and the image ships wpa_supplicant_s1g, hostapd_s1g, morse-bcf-info and batctl alongside the driver, with 802.11s + BATMAN-V already wired up.

Its mm610x-spi.dtbo uses the identical GPIO mapping we had arrived at by hand.

Lesson: search for prebuilt firmware before rebuilding a vendor driver. The SPI_NO_CS finding still stands for anyone running the Morse driver on a stock, unpatched kernel — but if you just want a working mesh node, flash OpenMANET.

See docs/openmanet.md.

Contents

Also worth reading

If you flash OpenWrt to SD cards with dd, docs/flashing-and-recovery.md is the most generally useful thing here. The image covers only the boot partition and the squashfs — the rootfs_data overlay after it is never written, so the device boots with its entire previous configuration restored while every verification you would normally run comes back green.

Status

• ✅ Driver probes, firmware + BCF load, netdev appears
• ✅ Root cause understood and patched
• ✅ OpenMANET 1.7.0 rpi4-mm6108-spi flashed, overlay wiped, booted and verified
• ✅ HaLow radio up under OpenMANET: RPI RPI4-MM6108 (SPI), wlan0, 923 MHz @ 2 MHz BW, 27 dBm
• ✅ Node 1 configured: 802.11s mesh + SAE, BATMAN_V, hostname manet01, 2.4 GHz off
• ✅ Two-LED field status indicator installed and verified — docs/led-indicator.md
• ✅ Node 2 built by cloning node 1's uci config, no wizard — docs/cloning-a-node.md
• ✅ Second MM6108 set probes and loads firmware, radio up at 923 MHz / 2 MHz
• ⏳ Two nodes not yet powered simultaneously, so the mesh has not been formed
• ⏳ TX still not proven to radiate — the first batctl n neighbour will settle it
• ⏳ meshtest written but not yet run against a real peer

License

Repository content is MIT (see LICENSE). The patch in patches/ applies to Morse Micro's driver, which is GPL-2.0-or-later; the patch is offered under the same terms as the code it modifies.