DDO Shows No Data

When a DDO displays its default value (0, empty, or no needle movement) instead of live data, follow these steps to diagnose the issue.

Quick Checklist

1. ✅ Is the Gateway running?
2. ✅ Is the SAMMI RTE running (s2_sysinit)?
3. ✅ Is the peer (data source) running?
4. ✅ Does the DDO have a Read Key configured?
5. ✅ Does the DDO have a Logical Server configured?
6. ✅ Does the logical server name match s2_config.dat?

Diagnosis Steps

Step 1: Check Gateway Connection

Look at the connection indicator in RuntimeWeb’s menu bar:

If disconnected, see Gateway Connection Issues.

Step 2: Verify the Peer is Running

The peer must be running and registered with SAMMI:

# Check if peer_fast is running
ps aux | grep peer_fast

# Verify RPC registration
rpcinfo -p localhost | grep 20000010

If the peer isn’t running, start it:

cd $SAMMI/contrib/peer_fast
./peer_fast -r 0x20000010 -E 1 &

Step 3: Check DDO Data Bindings

In StudioWeb, select the DDO and verify the HDA properties:

Step 4: Check s2_config.dat

The logical server name in the DDO must match an entry in SAMMI’s configuration:

# In $SAMMI/data/s2_config.dat:
logical_server  peer_fast   0x20000010    1   localhost   40  20

Common mismatch: DDO says peer_fast but config says Peer_Fast (case matters).

Step 5: Check Browser Console

Open browser DevTools (F12 → Console tab) and look for:

• WebSocket errors — connection refused, timeout
• Subscription messages — subscribe messages being sent
• Live value messages — liveValue messages being received

If you see subscriptions going out but no values coming back, the issue is on the SAMMI/peer side.

Step 6: Check DFD Number

For converted ASC pages, verify the DDO’s dfdNumber property matches SAMMI’s internal numbering. A mismatch causes values to route to the wrong DDO.

Common Causes

See Also

• Configuring Data Bindings
• Gateway Connection Issues
• Navigating RuntimeWeb