How to access Bluetooth LE features of CYW43439 on Raspberry Pi Pico W?

Question

Raspberry Pi Pico W comes with a chip, CYW43439, that is capable to do WiFi and Bluetooth (both Classic and LE). According to Chapter 2.1 in Raspberry Pi Pico W:s datasheet, GPIO24, GPIO25 and GPIO29 is used to communicate with the CYW43439 chip using SPI protocol.

Chapter 4.2 in CYW43439:s datasheet describes the generic SPI protocol interface, but Chapter 4 is the WLAN System Interface documentation. The same datasheet describes in Chapter 9.2, that UART is the interface for Bluetooth Host Controller Interface, HCI.

When programming on the RP2040 microcontroller, I should use the wired GPIO pins to use SPI to interface CYW43439, but how can I access the Bluetooth HCI from this SPI protocol?

There is a pico C SDK (that I don't really understand), but I would like to understand the interface to implement a driver in a different programming language.

Answer 1

I have now learnt that this is an undocumented area, so the only option is to use the pico C SDK (e.g. the suggestions in this issue).

I will consider to use a nRF chip instead, since they appear to be better documented when it comes to Bluetooth.