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Bluetooth HCI

Current Bluetooth Coprocessor firmware: https://github.com/lucasdietrich/zephyr-caniot-radio-coprocessor

Controller have a nrf52840 chip dedicated to bluetooth. Formerly, the bluetooth application was hosted on the BLE SoC. A custom UART protocol was used between the two chips to communicate.

With the new architecture, the bluetooth application runs on the main MCU, the BLE chip only run a HCI controller, and the two chips communicate over SPI. With this design, the bluetooth application is embedded with the main application.

This architecture is well documented in the description of the Dual-chip configuration in the Zephyr Bluetooth Stack Architecture documentation

PoC

In order to validate this architecture, following PoC was carried out:

  • Sample bluetooth/observer as HCI host with nucleo_f429zi board
  • Sample bluetooth/hci_spi as HCI controller with nrf52840dk_nrf52840 board

Wiring

Pin nrf52840dk_nrf52840 nucleo_f429zi Logic analyzer
CS P0.03 PA_4 1
MISO P0.04 PA_6 2
MOSI P0.05 PA_7 4
SCK P0.06 PA_5 3
IRQ P1.02 PF_12
RST P0.18 (RESET) PD_15

HCI Host - nucleo_f429zi

Following configuration options were added to prj.conf:

CONFIG_SPI=y

CONFIG_BT_HCI=y
CONFIG_BT_SPI=y
CONFIG_BT_CTLR=n

CONFIG_BT_DEBUG_LOG=n
CONFIG_BT_DEBUG_HCI_DRIVER=n

CONFIG_LOG=y
CONFIG_PRINTK=y

Devicetree overlay boards/nucleo_f429zi.overlay:

&spi1 {
	cs-gpios = <&gpioa 4 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>;
	status = "okay";

	hci-nrf52@0 {
		compatible = "zephyr,bt-hci-spi";
		reg = <0>;
		irq-gpios = <&gpiof 12 (GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)>;
		reset-gpios = <&gpiod 15 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>;
		spi-max-frequency = <2000000>; /* 2000000 */
	};
};

&gpiof {
	status = "okay";
};

So that the host receive BLE advertising frames continuously, scan parameters were changed to :

struct bt_le_scan_param scan_param = {
	.type       = BT_LE_SCAN_TYPE_PASSIVE,
	.options    = BT_LE_SCAN_OPT_NONE, /* No filtering on duplicates */
	.interval   = BT_GAP_SCAN_FAST_INTERVAL,
	.window     = BT_GAP_SCAN_FAST_WINDOW,
};

HCI Controller - nrf52840dk_nrf52840

Configuration file was kept as default.

Devicetree overlay boards/nrf52840dk_nrf52840.overlay:

&pinctrl {
	spi1_default_alt: spi1_default_alt {
		group1 {
			psels = <NRF_PSEL(SPIS_SCK, 0, 6)>,
				<NRF_PSEL(SPIS_MOSI, 0, 5)>,
				<NRF_PSEL(SPIS_MISO, 0, 4)>,
				<NRF_PSEL(SPIS_CSN, 0, 3)>;
		};
	};
};

&spi1 {
	compatible = "nordic,nrf-spis";
	status = "okay";
	def-char = <0x00>;
	pinctrl-0 = <&spi1_default_alt>;
	/delete-property/ pinctrl-1;
	pinctrl-names = "default";

	bt-hci@0 {
		compatible = "zephyr,bt-hci-spi-slave";
		reg = <0>;
		irq-gpios = <&gpio1 2 (GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)>;
	};
};

&uart1 {
	status = "disabled";
};

Following instruction was add at the very beginning of main function:

    /* Set GPIO voltage level to 3.3v, instead of default 1.8v*/
	NRF_UICR->REGOUT0 = UICR_REGOUT0_VOUT_3V3;

Expected result

Nucleo console expected output is:

*** Booting Zephyr OS build zephyr-v3.2.0-1-g817a0726429f  ***
Starting Observer Demo
Started scanning...
Exiting main thread.
Device found: A4:C1:38:8D:BA:B4 (public) (RSSI -50), type 0, AD data len 19
Device found: A4:C1:38:0A:1E:38 (public) (RSSI -59), type 0, AD data len 19
Device found: A4:C1:38:28:17:E3 (public) (RSSI -78), type 0, AD data len 19
Device found: A4:C1:38:EC:1C:6D (public) (RSSI -56), type 0, AD data len 19
Device found: A4:C1:38:68:05:63 (public) (RSSI -55), type 0, AD data len 19
Device found: A4:C1:38:A7:30:C4 (public) (RSSI -84), type 0, AD data len 19
Device found: A4:C1:38:68:05:63 (public) (RSSI -56), type 0, AD data len 19
Device found: A4:C1:38:E0:18:ED (public) (RSSI -72), type 0, AD data len 19
Device found: A4:C1:38:8D:BA:B4 (public) (RSSI -52), type 0, AD data len 19
Device found: A4:C1:38:0A:1E:38 (public) (RSSI -57), type 0, AD data len 19
Device found: A4:C1:38:28:17:E3 (public) (RSSI -78), type 0, AD data len 19

By monitoring the SPI bus with a logic analyzer, we can see the HCI frames exchanged between the two boards.