Wb Mod Slots

wb-mod-slots

Operate the per-slot hardware configuration on WB6/WB7/WB8 controllers — MOD1..MOD4 (internal WBE2 slots) and rs485-1..rs485-2. The slot's mode (RS-485, raw UART, bit-banged I2C, CAN, ...) is selected at runtime by loading a device-tree overlay through wb-hwconf-helper. Sister skill to wb-serial, which handles Modbus on top of the default RS-485 mode.

CRITICAL RULES

> Don't write /etc/wb-hardware.conf blindly. The file is the persistent config consumed at boot. A bad JSON or a wrong slot-id locks the slot into a non-working state on every reboot. For testing, prefer the runtime init/deinit path — it doesn't touch the conf file.

> init and deinit need the FULL board-prefixed slot-id (e.g. wb85-mod3, not mod3). The short mod3 form only works through config-apply against /etc/wb-hardware.conf. If wb-hwconf-helper complains "Slot definition file …/slots/mod3.def not found", you forgot the prefix.

> After init, expect a brief glitch on the slot's lines. Don't switch modes while another MCU on the wire is mid-transaction — pinmux flips can clock random bits and corrupt the peer's state.

> **` in examples** means wirenboard-.local` (substitute the controller's mDNS name).

When to load this skill

• User wants to expose raw UART or I2C on a MOD slot for a custom device, MCU programming, GPIO bit-bang, or one-off bench work.
• stty -F /dev/ttyMOD3 returns Input/output error even though the device file exists (= pinmux not applied yet).
• wb-mqtt-serial is configured to use /dev/ttyMODx but the port refuses to open.
• User mentions wb-hwconf-helper, /etc/wb-hardware.conf, wbe2x-generic-uart, wbe2x-generic-i2c, i2c-gpio, MOD slot mode, repurpose MOD3 / MOD4.
• User asks where /dev/i2c-modN came from or how to make one appear.

Stay out and hand off when:

• It's actually a Modbus/RS-485 diagnostics question on the default mode → wb-serial.
• Network adapters / WiFi / 4G → wb-network.

Architecture — what a MOD slot is

A MOD slot is an internal WBE2 connector on the controller. The CPU exposes a UART (or alternate functions: I2C, SPI, GPIO) on the slot's pins. What runs on those pins is decided at boot by an applied device-tree overlay. No overlay → pins are bare GPIOs in input mode → /dev/ttyMODx exists as a udev symlink but the underlying 8250 UART driver fails to talk to dead pinmux.

Layout on disk:

/etc/wb-hardware.conf                              # persistent user config (JSON)
/var/lib/wirenboard/hardware.state                 # current slot→module mapping (runtime)
/usr/share/wb-hwconf-manager/
├── boards/.conf                            # default modules per slot for this board
├── slots/-.def                       # slot pin map (e.g. wb85-mod3.def)
└── modules/.dtso  +  .sh          # overlay sources + add/remove hooks
/sys/firmware/devicetree/base/model                # current board hint

Board hint examples: Wiren Board rev. 8.5.1 (T507) → boards/wb85xm.conf. The mapping from DT compatible to boards/*.conf is in wb-hwconf-manager/config.py.

Tool: wb-hwconf-helper

wb-hwconf-helper init     # apply overlay now (non-persistent)
wb-hwconf-helper deinit            # roll back the active overlay on a slot
wb-hwconf-helper config-apply               # diff /etc/wb-hardware.conf vs current, apply
wb-hwconf-helper load-overlay        # apply a standalone DTS overlay
wb-hwconf-helper unload-overlay      # remove one
wb-hwconf-helper confed-tojson              # for the web editor
wb-hwconf-helper confed-fromjson            # for the web editor

` for init/deinit is the **full** id from boards/.conf (wb85-mod3, wb84-rs485-1, wb67-w1, …). The web editor uses the short form (mod3`) and resolves it through the board file; the CLI does not.

Workflow: switch a MOD slot's mode (runtime, recommended)

Switch MOD3 from default RS-485 to raw UART:

ssh root@ sudo wb-hwconf-helper init wb85-mod3 wbe2x-generic-uart
ssh root@ stty -F /dev/ttyMOD3        # should succeed now

Switch the same slot to bit-banged I2C:

ssh root@ sudo wb-hwconf-helper deinit wb85-mod3
ssh root@ sudo wb-hwconf-helper init wb85-mod3 wbe2x-generic-i2c
ssh root@ ls /dev/i2c-mod3 /dev/i2c-*  # the slot now appears as an i2c-gpio adapter

This path does not write to /etc/wb-hardware.conf. On the next reboot the slot reverts to the board default — desirable for bench tests, not for production use.

Workflow: persistent change (production)

Edit /etc/wb-hardware.conf:

{
  "slots": [
    { "slot_id": "mod3", "module": "wbe2x-generic-uart" }
  ]
}

Note: short slot_id here ("mod3"), not the board-prefixed form. The board file resolves it.

Apply:

ssh root@ sudo wb-hwconf-helper config-apply

config-apply diffs the new config vs /var/lib/wirenboard/hardware.state, calls deinit+init for each changed slot, and runs module add/remove hooks. Survives reboot.

Module catalogue (most common)

Names match files in /usr/share/wb-hwconf-manager/modules/. List the full set per board with ls /usr/share/wb-hwconf-manager/modules/ on the controller.

| Module | Exposes | Notes | | ----------------------- | -------------------------------------------------------- | ----- | | wbe2x-generic-uart | /dev/ttyMODn — raw UART on the slot's TX/RX | CPU UART, 3.3 V LVCMOS on T507. Check schematic for older boards. | | wbe2x-generic-i2c | /dev/i2c-modN — bit-banged i2c-gpio | TX→SDA, RX→SCL per wbe2-i2c.dtsi. ~100 kHz, no internal pull-ups. | | wb67-can-rs485 | RS-485 on rs485-1/2 slots | Default for rs485-* slots. | | wbe2-i-rs485-iso | Isolated RS-485 via WBE2-I-RS-485-ISO | For external WBE2 ISO modules. | | wbe2-i-rs232 | RS-232 | | | wbe2-i-can | CAN | Slot must be wbe2-i-can compatible (check boards/.conf). | | wbe2-i-knx | KNX | | | wb6-wx-1wire | 1-Wire on w1/w2 terminal mode | | | wbe2-i-w1 / -w1-gpio| 1-Wire on MOD slot | | | wbe2-i-opentherm | OpenTherm | |

If init fails with a DTS parse error, the slot likely doesn't match the module's compatible-slots — see the capability check below.

Slot capabilities — what fits where

Slots on the same board are NOT all equivalent. Each slot has a compatible: [...] list of tags; each module declares a single compatible-slots = "" string. A module loads on a slot iff the module's tag is in the slot's list.

Example on wb8.5 (/usr/share/wb-hwconf-manager/boards/wb85x.conf):

| Slot | Compat tags | I2C? | UART? | | ----------------- | --------------------------------------------------------------------------------- | :--: | :---: | | mod1 / mod2 | wbe2, wbe2-gpio, wbe3-reduced-uart, wbe3-wbec-only, wbe2-i-can | ✗ | ✓ | | mod3 / mod4 | wbe2, wbe2-gpio, wbe2-i2c, wbe3-reduced, wbe3-reduced-uart, wbe2-i-can | ✓ | ✓ | | rs485-1 / -2 | wb67-rs485 | ✗ | RS-485 only |

So wbe2x-generic-i2c (compatible-slots = wbe3-reduced) loads on mod3/mod4 but fails on mod1/mod2 — the agent must check capability before suggesting a slot. Same for analog modules (wbe2-ai-cm-1, wbe2-ao-10v-2) and RTC.

Run this on the controller to print the per-slot compatibility matrix for the current board:

ssh root@ python3  {', '.join(fitting) or '(none)'}")
PY

get_board_config_path() from wb-hwconf-manager/config.py resolves the right boards/.conf for whatever board you're on — don't hardcode the path. The CLI's ` is the value of the id field (e.g. wb85-mod3); the persistent-config short form is the slot_id field (mod3`).

Connector pinout (paste to user when they ask where to wire something)

Top view of the controller PCB. Pin 1 of the UART/I2C/GPIO block is the top-left of that block (3.3 V); odd numbers on the left column, even on the right.

MOD1..MOD3 on WB6.7–6.9 / WB7.x, MOD1..MOD4 on WB8.x:

       OUT1  ●  ●  OUT2
             ●  ●  OUT3
       ── 1 ─── 2 ──
       3.3V  ●  ●  5V
     TX/SDA  ●  ●  RTS
     RX/SCL  ●  ●  GND
       ═══ UART / I2C / GPIO ═══

MOD4 on WB6.7–6.9 / WB7.x (extra SPI block instead of OUTs):

       ── 1 ── SPI ── 2 ──
       MISO  ●  ●  MOSI
        SCK  ●  ●  CS
       ───────────────────
       3.3V  ●  ●  5V
     TX/SDA  ●  ●  RTS
     RX/SCL  ●  ●  GND
       ═══ UART / I2C / GPIO ═══

Pin function depends on the loaded module:

• wbe2x-generic-uart → TX (controller out), RX (controller in), RTS.
• wbe2x-generic-i2c → TX→SDA, RX→SCL (per wbe2-i2c.dtsi; remember external pull-ups, ~4.7 kΩ to 3.3 V).
• GPIO modules → bare digital lines.
• OUT1..OUT3 are passive contacts on the slot connector — they're routed to the controller's external (front-panel / terminal-block) connector. The installed WBE2 module decides what flows through them (e.g. relay contacts on a wbe2-do-* module). When you load wbe2x-generic-uart / -i2c there's nothing on them from the SoC side.
• SPI block (MOD4 on WB6.7–6.9 / WB7.x only) is a separate hardware SPI — wbe2-i-* SPI modules tap it.

Power rails per module (from the wiki): 3.3 V up to 0.5 A, 5 V up to 1 A. Wiki doesn't clarify whether the budget is per slot or shared across all four — assume shared and don't push it.

Signal lines are 0–3.3 V CMOS without overvoltage protection. Driving them from 5 V logic damages the controller — use a level shifter for any external 5 V peripheral.

Verify the switch worked

ssh root@ stty -F /dev/ttyMOD3              # OK = pinmux applied; Input/output error = no overlay
ssh root@ ls -l /dev/i2c-* /dev/ttyMOD*     # check expected device files exist
ssh root@ cat /sys/class/i2c-adapter/i2c-*/name | grep -i mod   # find which i2c-N is i2c-gpio
ssh root@ gpioinfo | grep -i "MOD3"         # if "unused input" — pinmux NOT applied
ssh root@ udevadm info -q all -n /dev/ttyMOD3   # which raw device backs the symlink
ssh root@ cat /var/lib/wirenboard/hardware.state    # what wb-hwconf-helper thinks is active

gpioinfo will keep showing MOD3 TX / MOD3 RX labels regardless of mode — the labels are static. Look at the third column: unused input means no overlay; an active overlay shows the pin as used by the kernel driver.

Pitfalls

• stty: Input/output error on a fresh /dev/ttyMODx — pinmux not applied. Run init for the slot or check /etc/wb-hardware.conf.
• wb-mqtt-serial config has the port with "enabled": false — the daemon does NOT set up pinmux for disabled ports. The port is "released" only in the wb-mqtt-serial sense; the kernel UART is still unmuxed until an overlay loads.
• Slot definition file …/slots/mod3.def not found on init — using short slot-id; needs the board-prefixed form (wb85-mod3).
• init errors with a DTS overlay parse error — the module's compatible-slots doesn't match the slot's compatible list. Run the capability matrix above to see which slots accept the module. Classic case on wb8.5: wbe2x-generic-i2c works on mod3/mod4 but fails on mod1/mod2.
• init succeeds but gpioinfo still says unused input — gpioinfo only sees pins that the kernel exposed as GPIOs. Pinmuxed pins (UART/I2C/...) leave the GPIO subsystem; the static labels stay. Check stty / /dev/i2c-* instead.
• wbe2x-generic-i2c is i2c-gpio (bit-banged), not hardware I2C. ~100 kHz max, no clock stretching support beyond what the kernel emulates. For real I2C performance use the SoC's hardware bus (/dev/i2c-1 etc.) on the side connector instead of MOD.
• No internal pull-ups on i2c-gpio. Add external pull-ups (4.7 kΩ to 3.3 V typical) on SDA and SCL.
• Switching modes while a device is connected can clock garbage during the brief transition between deinit and init. Power down the peer (or disconnect) before mode-switching if it's stateful.
• /etc/wb-hardware.conf = {} is normal — defaults from boards/.conf apply. The conf file only stores deviations from defaults.
• After deinit, /dev/ttyMODx symlink stays, but stty fails again. The symlink is created by udev based on the platform UART regardless of pinmux.

What the agent does NOT do

• Don't edit /etc/wb-hardware.conf for a one-off test. Use the runtime init/deinit path so a reboot returns to the board default.
• Don't replace an active rs485-1/rs485-2 module without checking what's on the bus. Existing Modbus devices will disconnect.
• Don't load an arbitrary .dtso via load-overlay from the internet. Only ship overlays from /usr/share/wb-hwconf-manager/modules/ or vetted local files; the kernel device-tree subsystem will happily activate dangerous configs.
• Don't claim that init+deinit cycle preserves bus signals. It doesn't — pins glitch.

When to ask the user

• The board model is uncertain (no /sys/firmware/devicetree/base/model or it doesn't map to a known boards/*.conf) — confirm the controller model before guessing the slot-id prefix.
• The target slot is currently rs485-* running production Modbus traffic — confirm before deinit (will break wb-mqtt-serial).
• The new mode requires extra hardware (pull-ups for I2C, isolation, level shifters) — surface that before flipping the mode and finding out the hard way.
• About to write /etc/wb-hardware.conf (persistent change) — confirm it should survive a reboot, not just one bench session.

Documentation

• WB hwconf-manager source:
• WB extension modules + pinouts + power specs (canonical):
• Linux i2c-gpio binding: kernel Documentation/devicetree/bindings/i2c/i2c-gpio.yaml
• Sister skill: wb-serial (Modbus/RTU on the default RS-485 mode).

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: wirenboard
• Source: wirenboard/wb-ai-skills
• License: MIT

Install and usage instructions live in the source repository linked above.