Disclaimer: This blog applies to following Cypress devices: CYW20706, CYW20719, CYW20735 and BT/BLE modules based on these devices.
Q. Using A2DP, how much is the expected minimum BT audio latency?
A. BT audio latency depends on many parameters like buffering on both source & sink sides, time required for PCM signals to playout, etc. The jitter buffer can be lowered to 4.1kB to give 50ms latency, but this comes with a cost of reduced audio quality. Therefore, in WICED, the jitter buffer is set to 116ms to avoid music interruptions caused by Wi-Fi and other radio sources. Setting it below 60ms will cause the buffer to overrun, a condition in which the buffer is fed with data at a slower rate than required, resulting in loss of audio.
Q. How to connect external host to Cypress BT chips?
A. Cypress BT chips can be used in host mode, where BT controller is controlled by an external host. We have a combo chip CYW943907WAE3 (check the workspace 43xxx_Wi-Fi), where CYW20707 gets programmed via 43907 MCU. In short, 43907 MCU acts as an external MCU for CYW20707. It takes the BT firmware from /43xxx_Wi-Fi/libraries/drivers/bluetooth/firmware/20706A2/40MHz/bt_firmware_controller.c and executes API bt_firmware_download().
To connect external MCU as host, host and controller should be connected via UART and then BT controller can be programmed by sending commands from Host. Cypress provides tools like ClientControl, CyBluetool for programming the device. Please refer <WICED workspace>/doc/WICED-HCI-Control-Protocol.pdf document for more details.
Note: CYW20707 is not a broad-market chip, but our module vendors like Murata use this chip to integrate it in a SiP along with other Wi-Fi chips. You can use CYW20706 to achieve similar functionalities.
Q. Do Cypress supports AT commands?
A. Cypress devices do not support AT commands. But we have EZ-Serial support for BT/BLE modules like CYBT-343026, CYBLE-022001 and more. Please refer following link for further details: https://www.cypress.com/documentation/software-and-drivers/ez-serial-ez-ble-module-firmware-platform
Q. How can I perform RF testing on Cypress BT devices/modules?
A. You can use mbt (<WICED workspace>/wiced_tools/mbt) or wmbt (<WICED workspace>/wiced_tools/wmbt) tools available in WICED SDK for RF testing. You can also use CyBluetool to allow DUT to enter different modes for regulatory test. Please refer attached pdf for more details.
- For BLE, you need to put device in HCI mode to accept commands through UART interface. For classic BT, put the device in Test mode to accept the commands through RF interface. Please refer section “Test Mode Setup” in attached pdf.
- MBT uses standard HCI commands and WMBT uses WICED HCI commands defined by Cypress.