BTstackTeensy -- Arduino library for Teensy 4.x + Murata Type 1YN (CYW43439)

An Arduino library packaging of BTstack for the Teensy 4.x family, talking to a Murata Type 1YN Wi-Fi+BT module (Cypress/Infineon CYW43439 silicon) over a 4-wire H4 UART. Provides:

• BLE Central & Peripheral (GAP/GATT), with the same wrapper API style as BlueKitchen's original port/arduino (BTstackManager/BTstack) -- renamed BTstackTeensyManager/BTstackTeensy here so both libraries can be installed side by side.
• Classic Bluetooth: A2DP Sink + AVRCP (audio out over Teensy Audio Library I2S1, e.g. an SGTL5000 Audio Shield) and HFP Hands-Free (voice audio bridged directly between the module and Teensy over its PCM interface, bypassing the host).

This packages the port as a modern "recursive src/" layout Arduino library, unlike the original port/arduino's flat/legacy layout.

Wiring

Signal	Teensy pin	Notes
HCI UART TX	35	Serial8 (LPUART6) TX -> module RX
HCI UART RX	34	Serial8 RX <- module TX
HCI UART RTS	36	hardware flow control, Teensy -> module CTS
HCI UART CTS	33	hardware flow control, module -> Teensy
BT_ON	28	module REG_ON / power enable, active high
BT_PCM_SYNC	3	SAI2 frame sync (LRCLK), module is clock master
BT_PCM_CLK	4	SAI2 bit clock (BCLK), module is clock master
BT_PCM_OUT	5	SAI2 TX data: Teensy -> module (mic path)
BT_PCM_IN	2	SAI2 RX data: module -> Teensy (speaker path)

Pins 2/3/4/5 are Teensy 4.x's second SAI block (SAI2, "I2S2" in Teensy Audio Library terms), wired in slave mode -- the CYW43439 drives the PCM clock (see ENABLE_SCO_OVER_PCM/ENABLE_BCM_PCM_WBS in src/btstack_config.h). This is separate from A2DP playback, which is decoded on the Teensy and sent out over I2S1 (the standard Teensy Audio Shield pins) via src/hal_audio_teensy.cpp.

All pins are overridable by defining BTSTACK_TEENSY_UART_PORT, BTSTACK_TEENSY_UART_RTS_PIN, BTSTACK_TEENSY_UART_CTS_PIN, BTSTACK_TEENSY_BT_ON_PIN and BTSTACK_TEENSY_BT_ON_SETTLE_MS as build flags before the library sources are compiled, if your wiring differs.

Firmware (patchram)

The CYW43439 needs its Bluetooth init script (patchram) loaded over HCI before it does anything. src/firmware/cyw43_btfw_1yn.h + src/firmware/cyw43_btfw_1yn_patchram.c provide a 1YN firmware blob from georgerobotics/cyw43-driver (the open-source Infineon/Raspberry Pi driver package that also backs the Pico 2 W's Bluetooth support -- see the file header there for provenance). This firmware blob is Murata/Infineon IP redistributed for use with their modules; it is not part of BTstack and isn't covered by this repository's license. Read Murata's or cyw43-driver's license/README before shipping a product with it. If you'd rather build your own from Murata's cyw-bt-patch repository instead, see chipset/bcm/convert_hcd.py in the main BTstack repository and replace the two files in src/firmware/ with its output.

Building the library

From this directory (port/arduino-teensy), with GNU Make, zip and a checkout of the full BTstack repository (the Makefile pulls BTstack's core, Classic, BLE and BCM chipset sources directly out of ../../src, ../../chipset etc. -- nothing is vendored into this folder):

make            # assemble build/BTstackTeensy and zip it to
                 # ../../btstack-arduino-teensy-<version>.zip
make install    # also copy build/BTstackTeensy into
                 # ~/Documents/Arduino/libraries/BTstackTeensy
make clean      # remove build/ and any previously built archives

Then, in the Arduino IDE: Sketch -> Include Library -> Add .ZIP Library... and select the generated archive (or just use make install and restart the IDE). Select a Teensy 4.x board (Tools -> Board -> Teensyduino) before compiling an example.

Examples

• BLEPeripheral, BLECentral, iBeacon, iBeaconScanner -- ported from port/arduino's BLE examples; the API is unchanged, only the global object name (BTstackTeensy instead of BTstack).
• A2DPSinkHFP -- Classic Bluetooth demo: A2DP Sink + AVRCP audio playback (wire an I2S DAC to Teensy's I2S1 pins to hear it) plus HFP Hands-Free call control over USB Serial (a answer, h hang up/reject, d<number> dial).

Known limitations

• Not yet run against real 1YN hardware as part of this port -- BT_ON timing, UART bring-up baud rate and PCM clock polarity/justification all need bring-up and debugging on your board. Start by watching the USB Serial log during hci_power_control(ON).
• No persistence: link keys and LE bonds live in RAM only -- every reboot forgets paired devices.
• A2DP only decodes SBC, and hal_audio_teensy.cpp doesn't resample: a source that negotiates 48/32/16 kHz instead of 44.1 kHz will play back at the wrong pitch/speed.
• AVRCP Target is a stub: the SDP record and connection are there, but volume/play-pause commands from the phone aren't wired to anything (avrcp_target_packet_handler in src/BTstackTeensy.cpp).