Troubleshoot control

Find the cause when a schematic, an Arc automation, or a script cannot control hardware.

Each entry starts from what you see, then gives the cause and the fix.

Schematics

The schematic has no control button

Cause

Your role is Viewer, or the schematic is a snapshot. A viewer cannot control hardware, and nobody can control a snapshot.

Fix

Ask an administrator for the Operator role or higher. For a snapshot, open the schematic that the snapshot came from.

A click on a valve does nothing

Cause

One of these:

• Editing is on, so the click selects the symbol.
• The schematic does not have control. Another writer with a higher authority holds the channel, or one with the same authority got it first.
• The command channel has no write task, or the symbol has no state channel, so the valve never shows as open.

Fix

1. Turn off editing, and take control.
2. Look at the control legend to see which writer controls the channel. To take over, see take absolute control.
3. Check the channels of the symbol. See what each symbol writes.

No symbols control any channels.

Cause

No symbol on the schematic has a command channel. The notification shows “Failed to acquire control”, with this text in the description.

Fix

Turn on editing, and set a channel in the Control tab of each symbol.

The schematic has no Control tab

Cause

Your role is Operator, or the schematic is a snapshot. Operators cannot edit schematics, so they write at authority 1.

Fix

Ask an administrator for the Engineer role.

Authority

Synnax drops commands with no error

Cause

Another writer controls the channel. Synnax drops writes from a writer that does not have control. It reports an error only when the writer opens, and only if the writer asks for it.

Fix

See which writer controls the channel. Then lower its authority, or raise yours above it.

<writer> has no control authority - it is currently held by <writer>

Cause

The writer asked for an error when it opens without control, and another writer holds the channel. The Python client.write method asks for it.

Fix

Stop the other writer, or open yours with a higher authority.

Authority 255 does not take control

Cause

On a channel with an index, a tie goes to the writer that got control first. A writer at 255 does not take control from another writer at 255. On a virtual channel, every writer at the controlling authority or above it writes.

Fix

Give automations a lower authority, such as 100, so that operators can take over at 255. See control authority.

An operator takes a channel from an automation, but commands do nothing

Cause

The automation sets a per-channel authority with no default, such as authority (vent_vlv_cmd 100). Its index channels stay at 255. The schematic also writes the index channel and loses it, so Synnax drops its writes to every channel on that index.

Fix

Give the authority line a default: authority (100 vent_vlv_cmd 200).

Arc automations

The stage indicator shows a running sequence, but the valves do not move

Cause

The automation has a lower authority than the schematic. A click on any button takes control of every actuated symbol on the schematic, valves included. Synnax then drops the commands from the sequence.

Fix

Keep the automation authority above the schematic authority, or put the start button on a separate schematic. See start a sequence from a schematic.

The abort stage runs at the end of a normal run

Cause

A write, a wait, or a gate step moves on to the next step in the code, also when the next step is a named stage. An abort stage right after such a step runs when the steps before it finish.

Fix

Put the abort stage where no step leads into it, such as after a stage that only leaves by name. See steps of a sequence.

The sequence runs once and never starts again

Cause

The sequence ends in a stage, so it never stops. A start command to a running sequence does nothing.

Fix

End the sequence with a write, a wait, or a gate, such as 0 -> vent_vlv_cmd. See when a sequence stops.

A transition does not fire when the stage starts

Cause

A stage reacts only to values that arrive after it starts. A condition such as tank_pt > 300 waits for the next tank_pt value, even when the last value was 400.

Fix

No fix is necessary when the sensor streams. See entering a stage.

The <type> node failed: WASM execution failed in node <key> at sample <i>/<n>: ...

Cause

A runtime error, such as an index out of bounds. On a Driver, the status shows “Failed to run Arc program” with this text in the description, and the automation stops. On the Core, the status shows “Node failed”, and the Core drops the cycle and keeps running.

Fix

Fix the code. See errors while it runs.

The automation list shows Stopped for a running automation

Cause

A known bug. The list shows Stopped when a running automation has a warning.

Fix

Open the automation to see its real status and the warning.

A Driver is not in the list

Cause

The list shows only Drivers with the arc integration turned on. All Drivers have it by default, but a Driver configuration can remove it.

Fix

Add arc to the integrations of the Driver. Deploy stays off until you choose a Driver.

undefined symbol: <name>

Cause

No channel, variable, or function has that name. Channel names are case sensitive.

Fix

Create the channel, or correct the name.

numeric conditions are deprecated; use an explicit comparison like x != 0

Cause

A number is used as a condition, such as start_cmd => press.

Fix

Compare it: start_cmd == 1 => press.

Graph editor

A block appears in the top-left corner

Cause

A click on a block in the menu puts it at the top-left corner of the graph.

Fix

Drag the block from the menu to where you want it.

An Add, Subtract, Multiply, Divide, or Not block does not compile

Cause

A known bug in these blocks.

Fix

Write the expression in a text automation. See compute values from channels.

A Change status block fires on every value

Cause

Graph edges pass every value, true or false.

Fix

Connect a Select block, and connect each Change status block to its true or false output. See build an alarm.

Python

Controller commands do nothing and raise no error

Cause

Another writer controls the channel. A Controller does not ask for an error, so Synnax drops its writes.

Fix

See Synnax drops commands with no error.

authorities: authority count must be 1 or equal to channel count

Cause

write_authorities has more than one value. The controller adds the index channels to its write channels, so the counts do not match.

Fix

Give one authority for all channels. Change it per channel with set_authority after the controller opens.

Channel ... not found in controller state

Cause

The code reads a channel that is not in the read list of the controller, or that has no value yet.

Fix

Add the channel to read, or wait for its first value with wait_until_defined.

The sequence goes on before the condition is true

Cause

wait_until returns False at the timeout. It raises no error.

Fix

Check the return value, and abort when it is False.