Paul Braeckel, in Advances in Computers, 2011 1.7 Protocol Stack and Profiles Some, however, do not support audio across HCI. When you make a choice of silicon, be aware that not every chip/chip set supports audio, so obviously you need to work with a chip/chip set that does! Of those that do support audio, most provide direct access to the baseband. However, if you are lucky enough to be involved in the choice early on, then in choosing a chip/chip set you should be aware of the potential impacts of choosing different interfaces to get audio into the Bluetooth subsystem. Often, by the time the application developer gets involved, hardware choices have already been made-which means you really have no choice of audio interface, and must work within the limitations of what you have.
BLUETOOTH STACK ANDROID SERIAL
To solve the problem of flow control affecting audio quality on serial links, the Bluetooth Special Interest Group (SIG)'s HCI working group is currently working on a new serial interface which will allow audio and data to be flow controlled separately.
BLUETOOTH STACK ANDROID DRIVERS
The problem does not arise if the USB transport is used for HCI, as this transport provides a separate channel for voice packets however, USB requires complex drivers and is not appropriate for all products. Buffering in the baseband chip could be used to prevent loss of data, but in practice, since audio signals are time-sensitive, any late samples are simply discarded, leading to gaps in the audio signal. If the Universal Asynchronous Receiver Transmitter (UART) HCI transport is used, there is no way to separately flow control voice and data, so when data transport is flow controlled, the flow of voice packets across the HCI will also stop. However, there is a second factor that can cause severe delays and lead to loss of SCO packets: this is flow control of the HCI interface. The time taken for the Bluetooth subsystem's microcontroller to transfer the audio data from the baseband into HCI packets introduces some delay, but this is imperceptible. The only difference between the two routes through the system is that all packets passing through HCI experience some latency. Audio Is Part of the Baseband Protocol Stack
0 kommentar(er)
