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Introduction

RootCanal is a virtual Bluetooth Controller. RootCanal aims reducing the overhead of writing and deploying end-to-end tests on Bluetooth devices by taking away the physical layer.

Feature emulation

The emulation of Bluetooth features on RootCanal is limited to features that have direct consequences on connected hosts. The accurate implementation of HCI commands and events is thus critical to RootCanal's goal, while accurate emulation of the scheduler and base-band is out of scope.

Usage

Emulator integration

RootCanal is natively integrated in the Cuttlefish and Goldfish emulators. Bluetooth is enabled by default on these platforms. External hosts can connect to the HCI port 7300 to interact with the emulated device.

Standalone tool

RootCanal can be built and started as a standalone tool. Instructions to build and run root-canal from an AOSP instance:

source build/envsetup.sh
lunch aosp_cf_x86_64_phone-userdebug
m root-canal
./out/host/linux-x86/bin/root-canal

Note: You can also find a prebuilt version inside cvd-host_package.tar.gz from Android CI The following configuration options are implemented:

  • --test_port (default 6401) Configure the TCP port for the test channel.

  • --hci_port (default 6402) Configure the TCP port for the HCI server.

  • --link_port (default 6403) Configure the TCP port for the link server.

  • --link_ble_port (default 6404) Configure the TCP port for the BLE link server.

  • --controller_properties_file (default "") Configure the path to a custom Controller configuration file. All properties defined in model/controller/controller_properties.h can be edited to test with a specific controller setup.

  • --enable_hci_sniffer (default false) Capture PCAP traces for all connected HCI hosts. The PCAP traces are saved in the current directory.

  • --enable_baseband_sniffer (default false) Capture PCAP traces for all base-band packets exchanged between connection HCI hosts. The PCAP traces are saved in the current directory. This option is useful to inspect and debug RootCanal's implementation.

Architecture

All RootCanal instances expose four TCP ports:

  • HCI channel
  • Test channel
  • BR_EDR Phy channel
  • LE Phy channel

HCI Channel

The HCI channel implements the Bluetooth UART transport protocol (a.k.a. H4) over TCP. Each new connection on the HCI port spawns a new virtual controller.

Test Channel

The test channel uses a simple custom protocol to send control commands to RootCanal. You can connect to it using scripts/test_channel.py.

Phy Channels

The physical channels use a custom protocol described in packets/link_layer_packets.pdl. The protocol simplifies the LL and LMP protocol packets defined in the Bluetooth specification to abstract over negotiation details.

Warning The protocol can change in backward incompatible ways, be careful when depending on it.

Controllers can exchanges link layer packets only when they are part of the same phy. One controller can be added to multiple phys, the simplest example begin BR/EDR and LE dual phys.

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