Architecture of bluetooth low energy tws earbuds apple

link layer

The link layer is the most complex part of the Bluetooth low energy architecture. It is responsible for broadcasting, scanning, establishing and maintaining connections, as well as ensuring that data packets are organized in the correct way, checksums and encryption sequences are calculated correctly, etc. In order to realize the above functions, the following three basic concepts are defined; channel, message and process. www.bjbjaudio.com

There are two types of link layer channels: broadcast channels and data channels. Devices that are not connected use the broadcast channel to send data. There are three broadcast channels - again, this number is a compromise between low power consumption and robustness. Devices use this channel to broadcast to advertise themselves as connectable or discoverable, and perform scans or initiate connections. After the connection is established, the device utilizes the data channel to transmit data. There are 37 data channels in total, controlled by an adaptive frequency hopping engine for robustness. In a data channel, one end is allowed to send data to the other, acknowledging it, and retransmitting it if needed, in addition to encrypting and authenticating each packet.

Data sent on any channel (including broadcast channels and data channels) are small packets. The data packet encapsulates a small amount of data from the sender to the receiver, and a checksum to ensure the correctness of the data. Whether in broadcast channel or data channel. The basic packet format is the same. Each data contains a minimum of 80 bits of address, header and check information. www.bjbjaudio.com

Host/Controller Interface

For many devices, the advent of the host/controller interface (HCI) provides a standard interface for the host to communicate with the controller. This structural division is prevalent in classic Bluetooth. More than 60% of Bluetooth controllers use the HCI interface. It allows the host to send commands and data to the controller, and it allows the controller to send events and data to the host. The host/controller interface actually consists of two separate parts: the logical interface and the physical interface. www.bjbjaudio.com

Logical interfaces define commands and events and their associated behaviors. The logical interface can be delivered to any physical transport, or to the controller via a native application programming interface (API) located on the controller, which can contain an embedded host protocol stack.

The physical interface defines how commands, events, and data are transferred through different connection technologies. The defined physical interfaces include USB, SDIO, and two UART@ variants. For most controllers, they only support one or two interfaces. Considering that implementing a USB interface requires a lot of hardware and is not a low-power interface, it usually does not appear on single-mode controllers for Bluetooth low energy. Because the host controller interface exists within the controller and host, the portion that resides in the controller is often referred to as the lower portion of the host controller interface: the portion that resides in the host is typically referred to as the upper portion of the host controller interface. www.bjbjaudio.com