Device Interfaces

The XVF3800 supports a range of interfaces which allows integration of the device into multiple applications.

Audio Interfaces

Audio Master Clock (MCLK)

The XVF3800 uses a master audio clock (MCLK) to drive the internal pipeline processing.

The MCLK signal can be derived from one of two sources.

1 - Internal MCLK

The MCLK signal is generated internally in the XVF3800 using a Phase Locked Loop (PLL) that uses the I²S clock or USB frame clock as the timing reference.

Table 4 Signal in internal MCLK mode

Signal	Description	Comment	Pin	I/O
MCLK_INOUT	Master audio clock output	Output - Connect to pin 41	14	O
MCLK	Master audio clock	Connect to pin 14	41	I
I2S_BCLK	I2S bit synchronisation clock	Configurable for 16 kHz (1.024 MHz) and 48 kHz (3.072 MHz) sample rates	13	I
I2S_LRCK	I2S Left/Right clock		10	I
USB_DM	USB data	UA configuration only	28	I
USB_DP	USB data	UA configuration only	29	I

Note

This mode is the only clock mode supported in the UA configurations. The audio output stream provides the reference signal for the internal PLL.

2 - External MCLK

The host system can supply a master clock to the XVF3800. This signal must be synchronised to the I²S clock for correct operation. A 12.288 MHz clock frequency is recommended, but this can be modified in the system firmware if required.

Table 5 Signals in external MCLK mode

Signal	Description	Comment	Pin	I/O
MCLK_INOUT	Master audio clock input		14	I
MCLK	Master audio clock	Connected to pin 14	41	I
I2S_BCLK	I2S bit synchronisation clock	Configurable for 16 kHz (1.024 MHz) and 48 kHz (3.072 MHz) sample rates	13	I
I2S_LRCK	I2S Left/Right clock		10	I

Note

The XVF3800 requires 32b clocks per sample on the I²S interface.

PDM Microphone Inputs

Four standard PDM MEMS microphones should be connected to the MIC_DATA[0..3] pins. The XVF3800 outputs a clock at 3.072 MHz on the MIC_CLK output, which must be fed directly to all microphones. This clock is derived from the MLCK and must be used to clock the microphone PDM output to avoid undefined artefacts in the processed audio stream.

The XVF3800 voice processor has been tested and characterised with microphones in a linear array placed with a 33 mm separation and a square array with a 66 mm spacing. Other spacings with a maximum spacing of 100 mm are possible, but uncharacterised.

These microphones should be connected to the product enclosure in such a way that the acoustic path to each microphone from outside the product is independent. The XVF3800 algorithms are configured as part of the firmware build configuration.

Audio Interface

The XVF3800 supports a flexible set of audio interface types. The specific interfaces of a device is set by the configuration chosen when the firmware image is built.

In INT-Device configurations the XVF3800 operates as an I²S slave receiving a reference audio signal from the host and returning processed microphone signals to the host. This bidirectional flow of audio samples must be synchronised to a single set of I²S clocks, see the table below:

Table 6 I²S signals in INT-Device configurations

Signal	Description	Comment	Pin	I/O
MCLK	Master audio clock		14	I/O
I2S_BCLK	I2S bit synchronisation clock	Configurable for 16 kHz (1.024 MHz) and 48 kHz (3.072 MHz) sample rates	13	I
I2S_LRCK	I2S Left/Right clock	48 kHz or 16 kHz clock derived as I2S_BLCK/64	10	I
I2S_DATA0	I2S Data In	Reference audio data from I2S device	9	I
I2S_DATA1	I2S Data Out	Audio data out to host processor	39	O
I2S_DATA2	I2S Data Out	Audio data out to DAC	53	O

The I²S audio samples are transmitted serially with a delay of one I2S_BCLK cycle between the change of I2S_LRCK phase and the start (MSB) of the audio sample for that channel. This the standard alignment for I²S systems.

In UA configurations the audio signals to and from the host system are carried over a USB connection. The XVF3800 operates in USB Adaptive Mode to synchronise with the host. In this configuration the I²S interface operates in master mode to supply the far end audio signal to the DAC driving the speaker.

Table 7 I²S signals in UA configurations

Signal	Description	Comment	Pin	I/O
MCLK	Master audio clock		14	I/O
I2S_BCLK	I2S bit synchronisation clock	Configurable for 16 kHz (1.024 MHz) and 48 kHz (3.072 MHz) sample rates	13	O
I2S_LRCK	I2S Left/Right clock	48 kHz or 16 kHz clock derived as I2S_BLCK/64	10	O
I2S_DATA0	I2S Data Out	Audio data out to DAC	9	O
I2S_DATA1	I2S Data In	Optional reference audio data in	39	I

Integrated USB Interface

The XVF3800 includes an integrated USB 2.0 PHY supporting Audio Class 2.0 running at High Speed (480 Mbps). This interface is used by the USB host to output a far end signal to a DAC and loudspeaker, to receive processed microphone signals from the XVF3800 audio pipeline and to allow the host to control the operation of the device. In this mode the adaptive USB Audio endpoint is used to generate an MCLK synchronised to the USB host output stream rate. This is provided via the MCLK output on the device. In the case of no output stream being available, the MLCK output is set to a nominal 12.288 MHz.

The table below shows the signals required to implement a USB interface using the XVF3800.

Table 8 USB connections

Name	Description	Pin
USB_DP	Connect to USB connector	29
USB_DM	Connect to USB connector	28
USB_VDD18	1.8V supply for USB-PHY - May be left floating if the USB interface is not used	31
USB_VDD33	3.3V supply to the USB-PHY May be left floating if the USB interface is not used	30
USB_VBUS _DET	Note: Self-powered operation is not supported by current device firmware	N/A

System firmware

QSPI Boot Mode

When QSPI boot mode is enabled (default), the XVF3800 enables six QSPI pins and drives the QSPI clock as a QSPI Master.

For further information about the boot sequence refer to the XU316-1024-QF60B datasheet.

Host boot via SPI

The SPI interface can be utilised by a host controller to download the XVF3800 firmware to boot the device. Details of the SPI boot protocol can be found in the XVF3800 User Guide.

To enable the SPI boot from an external host processor, the QSPI_D1/BOOTSEL should be pulled to VDDIO on power-up. This activates the SPI interface, which operates as a slave to the host processor for the transfer of the boot image, which is clocked in with the least significant bit first in each transferred byte.

This is an alternative to using an attached QSPI flash to automatically transfer boot data on start-up.

The SPI pins are shown in the table below.

Table 9 SPI signals

Signal	Description	Comment	Pin	I/O
SPI_CLK	SPI Clock		5	I
SPI_CS_N	SPI Chip Select	Pull high externally to the device using a 4.7k ohm resistor	6	I
SPI_MOSI	SPI Master Out Slave In		7	I
SPI_MISO	SPI Master In Slave Out	May be left floating if not required for control	47	O

Device Control Interface

The XVF3800 has a control framework that can be used to update device parameters and read data from the audio pipeline and the I/O pins.

Three protocols options are supported - USB, SPI or I²C. The protocol is set as a compile time option when the firmware image is built. Only one protocol can be active in a specific configuration, but the same control commands are available via all interface types.

Warning

Some commands have no effect on device operation if they are not valid for the configuration in use.

A host control application is provided in the firmware release package that implements the control protocol and provides a user interface for the XVF3800 device.

Note

Only one control protocol, USB, SPI or I²C can be used in a specific implementation. This choice is set in the firmware and cannot be changed during operation of the device.

USB Control Interface

In the UA configuration of the XVF3800, the control interface is available via the USB Endpoint 0.

I²C Control Interface

The I²C slave interface is used to control and configure the parameters on the XVF3800.

The interface operates with the following specifications:

• 100 kbps SCL clock speed

• Register read/write

• Up to 60 byte I²C read/write

The device I²C address is 0x2C, and the pin connections are shown below.

Table 10 I²C slave connections

Signal	Description	Comment	Pin	I/O
I2C_SCL	I2C serial clock line for receiving control command from I2C host		44	I/O
I2C_SDA	I2C serial data line for receiving control command from I2C host		45	I/O

SPI Control Interface

The SPI slave interface can used to control and configure the parameters on the XVF3800.

Note

Only one control protocol, SPI or I²C can be used in a specific implementation. This choice is set in the firmware and cannot be changed while the device is operating.

SPI pin connections appear in Table 9. For more information on control and configuration of the XVF3800 please refer to the User Guide.

General Purpose Input/Output

Two input and five output pins are provided to allow general-purpose I/O (GPIO) such as LEDs and button controls. Input pins can be individually read by the host using the control interface and configured to detect edge events. The output pins can be individually set, and they have configurable Pulse Width Modulated (PWM) brightness control with blinking sequences.

The INT_N pin provides a hardware interrupt to the host system to indicate if a GPI has been triggered. The behaviour of this pin, e.g. which GPI, which edge etc, can be configured via the control interface.

The standard allocation of the GPIO pins in the XK-VOICE-SQ66 development kit is shown in the table below, but these can be adapted in the device firmware for other uses if required for a specific design.

Table 11 GPIO pin table

Name	Description	Pin	I/O
P_BUTTON_0	Input for ‘Mute’ button	11	I
P_BUTTON_1	Input for ‘Action’ button	32	I
CODEC_RST_N	GPO for driving reset of conected DAC or digital amplifier	40	O
SQ_nLIN	GPO for selecting topology mode of microphones	54	O
INT_N	GPO for signalling an interrupt to the host	55	O
LED_R	Red element of tri-colour LED	56	O
LED_G	Green element of tri-colour LED	57	O

For more information on configuring these inputs and outputs, please refer to the XVF3800 User Guide.

I²C-to-IO expander

The number of input and output pins can be extended using an I²C-to-IO expander. The IO expander can be attached to the XK-VOICE-SQ66 development kit, and the XVF3800 firmware can be configured to use the additional pins for GPIO over I²C.