SILICON LABS UG513 BT122 HCI Mode User Guide
- June 6, 2024
- SILICON LABS
Table of Contents
UG513: BT122 HCI Mode User’s Guide
The document contains general assumptions of the HCI model implementation.
KEY FEATURES
- HCI Mode support
- DFU over UART possible in HCI mode
- Bluetooth host flexibility
General Assumptions
Connection to the Host
In the HCI mode, the BT122 module acts as a Bluetooth controller (according to the Bluetooth Core nomenclature). HCI mode also requires a connection to a host device, which is achieved using UART interface as the main way of communication and control of the BT122 module.
General Rules
BT122 module is based on two main parts:
- Texas Instruments CC2564C Bluetooth Dual Mode controller
- Silicon Labs microcontroller
After restart, the microcontroller initializes the TI radio chip by sending all needed vendor settings and configurations. Next, the microcontroller provides Silicon Labs Bluetooth Stack (the BT Host implementation) and uses that to communicate with the TI controller via the HCI protocol, as described in the Bluetooth Core Specification. In the HCI mode, the microcontroller is also responsible for the TI chip initialization and handling vendor commands. However, after that routine, all HCI commands, events, and responses will be passed to and from the main BT122 UART port.
The Initial Proposal for the HCI Mode Firmware Preparation
To create any BT122 project, prepare XML configuration files that are used by BGBuild.exe to generate end firmware. The same concept is used to generate the HCI mode firmware, as follows:
-
Update the UART setting in hardware.xml file, for example:
-
Include a proper library in project.xml file:
Additionally, it is possible to turn on a sleep mode.
For more details, see UG496: BT122 Project Configuration User’s Guide.
HCI Mode Comparison for iWRAP and BT122
Table 2.1. Comparison of HCI Mode on iWRAP and BT122
| Feature | iWRAP | BT122 |
|---|---|---|
| HCI protocol | BCSP, H4 | H4 |
| Interfaces | UART, USB | UART |
| UART baud rate | Configurable, up to 3686400 bps | Configurable, up to 3 Mbps |
| A way of launching the HCI mode | iWRAP command; the setting of a proper value | |
| in a dedicated PSKey | The setting of the HCI mode in an XML configuration file |
before building the firmware
Using BT122 Module with Host Bluetooth Stack
Custom Module Configuration
Three API commands are available in HCI mode, as follows:
- dumo_cmd_system_reset
- dumo_cmd_hardware_set_uart_configuration
- dumo_cmd_system_get_info
See BT122 Dual Mode API Reference for detailed command documentation. To
configure the serial port, type expected parameter values into the hardware
configuration (see UG496: BT122 Project Configuration User’s Guide) or use the
dumo_cmd_hardware_set_uart_configuration command.
To update firmware, reset the module in DFU mode with the
dumo_cmd_system_reset command. Next, update firmware according to section 4.3
of UG497: BT122 User’s Guide.
BlueZ Stack Example
BT122 module, flashed with HCI firmware, is ready to work with the host
Bluetooth stack, for example, BlueZ stack. The following are example
configuration steps on the code snippet below.
Because of resource limitations, set the maximum ACL packet length up to 350
bytes.
The highest stable serial port baud rate (for HCI mode) is 2 Mb/s. A higher
serial port baud rate is not recommended for host Bluetooth stacks.
$ sudo attach /dev/ttyUSB0 any 2000000
$ sudo hciconfig hci0 aclmtu 350:3
$ sudo hciconfig hci0 up
After correct configuration, BT122 works as Bluetooth dual-mode device.
$ hciconfig
hci0: Type: Primary Bus: UART
BD Address: C4:64:E3:63:8A:AE ACL MTU: 350:3 SCO MTU: 180:4
UP RUNNING
RX bytes:21035348 acl:1089757 sco:0 events:722081 errors:0
TX bytes:79735765 acl:1137257 sco:0 commands:96 errors:0
References
- Silicon Labs, BT122 Dual Mode API Reference, 2021
- Silicon Labs, UG496: BT122 Project Configuration User’s Guide, 2021
- Silicon Labs, UG497: BT122 User’s Guide, 2021
Version History
Revision 1.0
October 2021
- Initial release.
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