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LogScope Docs

HCI Packet Decoding

LogScope can decode Bluetooth LE HCI (Host Controller Interface) packets in real-time when using J-Link RTT with Zephyr firmware that has the BT Monitor enabled.

Enabling HCI Tracing

Section titled “Enabling HCI Tracing”

Add these to your Zephyr firmware’s prj.conf:

CONFIG_BT_DEBUG_MONITOR_RTT=y

This enables the BT Monitor protocol on RTT Channel 1, which streams HCI packets alongside your regular log output on Channel 0.

What You’ll See

Section titled “What You’ll See”

HCI packets appear in the log viewer with:

  • Purple “HCI” severity label and purple left border
  • Module column showing the packet direction: CMD (host to controller), EVT (controller to host), ACL (data)
  • Message column with a decoded summary (e.g., “LE Set Advertising Parameters (interval: 48-96, type: 0)“)

Expandable Detail Views

Section titled “Expandable Detail Views”

HCI rows with decoded data show a small triangle icon. Click to expand and see:

  • Field table: Named fields with decoded values (e.g., “Adv Interval Min: 48”, “Adv Type: 0”)
  • Color-coded values: Status fields are colored (green for success, red for errors)
  • Raw hex dump: Click “Show raw hex” to see the raw packet bytes in a formatted hex dump

Click the row again to collapse.

HCI vs MON

Section titled “HCI vs MON”

The BT Monitor protocol carries two types of data:

  • HCI packets (CMD, EVT, ACL) - Real Bluetooth LE protocol traffic between the host and controller
  • MON messages - Debug strings that the Bluetooth stack mirrors to the monitor channel

By default, MON messages are hidden. Use the MON toggle button in the filter bar to show them. The sidebar “HCI Packets” counter only counts real HCI protocol packets, not MON messages.

Exporting HCI Packets

Section titled “Exporting HCI Packets”

Export captured HCI packets in Wireshark btsnoop format for detailed protocol analysis:

  1. Click Export in the connection bar
  2. Select Wireshark (.btsnoop)
  3. Open the file in Wireshark

The btsnoop export includes only HCI packets (not regular log entries or MON messages).

Supported Packets

Section titled “Supported Packets”

LogScope decodes common HCI commands and events including:

  • LE Set Advertising Parameters/Data/Enable
  • LE Set Scan Parameters/Enable
  • LE Create Connection
  • LE Connection Complete
  • LE Connection Update
  • LE Read Remote Features
  • Disconnect
  • Read BD ADDR
  • Set Event Mask
  • Command Complete/Status events

Packets with unknown opcodes are displayed with the raw opcode value and can still be expanded for hex dump inspection.