Voice Over Remote Control

Application Report SWRA506 – May 2016

Voice Over Remote Control Torbjorn Sorby ABSTRACT This application report describes the voice over RF protocol used for Texas Instruments Bluetooth® low energy (BLE) and RF4CE remote control solutions.

1

Contents Introduction ................................................................................................................... 2 List of Figures

1 2 3 4 5 6

....................................................................................................................... CC2541 ....................................................................................................................... CC2650 ....................................................................................................................... RF4CE ........................................................................................................................ BLE ............................................................................................................................ Sequence Diagram .......................................................................................................... CC2533

3 3 3 4 4 7

List of Tables

..............................................................................................

1

Abbreviations and Acronyms

2

Start Frame ................................................................................................................... 4

2

3

IMA-ADPCM Data Frame ................................................................................................... 5

4

Stop Frame ................................................................................................................... 5

5

Raw PCM Data Frame ...................................................................................................... 5

6

Start Frame ................................................................................................................... 5

7

BLE ADPCM Data Frame Part #1/5 Frame .............................................................................. 5

8

BLE ADPCM Data Frame Part #2/5 Frame .............................................................................. 5

9

BLE ADPCM Data Frame Part #3/5 Frame .............................................................................. 6

10

BLE ADPCM Data Frame Part #4/5 Frame .............................................................................. 6

11

BLE ADPCM Data Frame Part #5/5 Frame .............................................................................. 6

12

Stop Frame ................................................................................................................... 6

Bluetooth is a registered trademark of Bluetooth SIG, Inc . All other trademarks are the property of their respective owners. SWRA506 – May 2016 Submit Documentation Feedback

Voice Over Remote Control Copyright © 2016, Texas Instruments Incorporated

1

Introduction

1

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Introduction Sending voice data over a low-power wireless protocol enables multiple use cases, such as, voice recognition or baby monitoring. This application report presents the fundamental concepts of the voice implementation used in Texas Instruments BLE and RF4CE remote control solutions.

1.1

Main Features • • • • •

1.1.1

16 kHz sampling rate, 16 bits resolution 4:1 compression perform on-chip Required throughput -- 64 kbps RF4CE application throughput up to 90 kbps BLE application throughput is higher than RF4CE and dependent on the system Abbreviations and Acronyms Table 1. Abbreviations and Acronyms BLE

Bluetooth Low Energy

FA

Frequency Agility

I2C

Inter-IC

I2S

Inter-IC Sound

IC

Integrated Circuit

IMA-ADPCM kbps LL

Kilo bits per second Link Layer

MAC

Medium Access Control

NWK

Network Layer

PDM

Pulse Density Modulation

RC

Remote Control

RF

Radio Frequency

RF4CE SPI

2

Interactive Multimedia Association-Adaptive Differential Pulse Code Modulation

Radio Frequency for Consumer Electronics Serial Peripheral Interface

Voice Over Remote Control

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1.2 1.2.1

Solutions Block Diagram There are multiple devices available from Texas Instruments and Figure 1 through Figure 3 show the components used in the various voice enabled Remote Controllers. In case of the CC25xx generation, an external codec is connected to an analog microphone. It is configured via inter-integrated circuit (I2C) and audio is retrieved via inter-IC sound (I2S). The master clock is provided by CC25xx, which also acts as an I2S slave. The I2S slave is implemented using the serial peripheral interface (SPI) module in slave operation, with a word clock connected to the chip select pin. In the CC26xx devices, no external codec is required as the bit stream from a digital microphone can be read directly by the device, and the PDM stream can be processed in software.

IN

3xAAA

3xAAA

LDO

LDO

VDD

MOSI

DOUT BCLK

SCLK

WCLK

CSN

IN

VDD

MOSI

DOUT BCLK

SCLK

WCLK

CSN

Audio Codec: TLV320ADC3101

Audio Codec: TLV320ADC3101

CC2541

CC2533 GPIO/Timer

MCLK

GPIO/Timer

Reset

GPIO (reset)

Reset

GPIO (reset)

I2C-S

I2C-M

I2C-S

I2C-M

MCLK

GPIOs

GPIOs

User Interface: (buttons/buzzer)

User Interface: (buttons/buzzer)

32 kHz Xtal

32 MHz Xtal

32 MHz Xtal

I2C-S

I2C-S MEMS (gyro, accel)

MEMS (gyro, accel)

Figure 1. CC2533

Figure 2. CC2541 2xAAA

VDD

ADI BCLK

CC2650 I2C-S MEMS (gyro, accel)

I2C-M

User Interface: (buttons/buzzer)

GPIOs

32 kHz Xtal

24 MHz Xtal

Figure 3. CC2650

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1.2.2

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Audio Flow Diagram Figure 4 and Figure 5 show various audio flows from the microphone via RF to speaker. Controller Node

Target Node PDM

PDM

PCM

ADPCM Encoding

RF4CE nwk + MAC Tx

ADPCM Decoding

RF4CE nwk + MAC Rx

USB Audio USB HID

Application

CC26xx RF4CE

ADC

I2S Tx

I2S/SPI

SPI Rx

Audio Codec: TLV320IDC3101

ADPCM Encoding

Any device which supports USB Audio, e.g. PC or MAC

File

CC2531 ZRC Audio Dongle Target Node

Controller Node Digital IN Filtering

USB

RF4CE to HID

RF4CE nwk + MAC Rx

RF4CE nwk + MAC Tx

CC2533 RNP

UART/SPI/I2C

NPI

ADPCM Decoding File

Application running on Host, using remoTI network interface

CC2533

Figure 4. RF4CE Audio Central / HID Host Audio Peripheral / HID Client

PDM

PCM

Vendor HID Voice over HID over GATT

Voice over HID over GATT

ADPCM Encoding

USB

. Alt

Voice over HID over GATT

BLE Audio Peripheral / HID Client Digital IN Filtering

I2S Tx

SPI Rx

I2S/SPI

ADPCM Encoding

Alt.

Voice over GATT

Voice over HID over GATT

Alt.

Audio Codec: TLV320IDC3101

ADPCM Decoding

HID Keyboard/Mouse/ Consumer Control

File

Audio Central / HID Host

CC26xx

ADC

USB

CC2540

Voice over GATT

ADPCM Decoding

Any device which supports USB Audio, e.g. PC or MAC Also include HID Keyboard/ Mouse/Consumer Control

USB

File

CC2540 Voice over GATT

Audio Central / HID Host / Mobile Device (iOS or Android)

CC2541

Voice over HID over GATT

Andro id only

ADPCM Decoding

USB

PDM

File

Voice over GATT

HTML SensorTag Application

Figure 5. BLE

1.2.3

Audio Protocol In order to transmit audio data over BLE or RF4CE, it is necessary to have a protocol in place. A protocol defines rules on how to interpret data. To save power, do not transmit audio continuously. As such, an audio stream has a finite beginning and end. In addition to indicating the audio data, the beginning of transmission can be identified as well as the end. This has the added benefit of allowing the recipient to prepare for an audio stream.

1.2.3.1

RF4CE

To improve rate, re-transmission on different channels can be removed, which is necessary to re-acquire channels in case they are changed mid-stream. Locking the RF channel removes this need. For RF4CE, there is a very easy way to transmit your own vendor specific data, which is simply called vendor specific data transmission. Since there is no official protocol to transmit audio data, vendor specific data is used. Texas Instruments already defines several vendor specific data protocols, such as an Overthe-Air-Download protocol and a latency test protocol. Table 2. Start Frame Number of Bytes Field

4

1

1

1

1

1

Protocol ID

CMD ID

Sample Frequency

Sample Width

Mode

0x50

0x00

8: 8kHz 16: 16kHz

8, 12 or 16 bits

0: RAW 1: IMA-ADPCM

Voice Over Remote Control

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Table 3. IMA-ADPCM Data Frame Number of Bytes

1

1

Protocol ID Field

Seq No

ID

[7:3]

[2:0]

0-31

0x01

0x50

1

1

1

var

Header 1

Header 2

Header 3

Audio Samples

Table 4. Stop Frame Number of Bytes Field

1

1

Prot/ocol ID

CMD ID

0x50

0x02

Table 5. Raw PCM Data Frame Number of Bytes Field

1.2.3.2

1

1

1

var

Protocol ID

CMD ID

Seq No

Audio Samples

0x50

0x03

0-255

16 bits LSB PCM

BLE

There is no standard way of transmitting audio via BLE. It is, however, quite simple to wrap the audio data into a vendor defined profile service. One such option is vendor defined characteristics where audio is transmitted over GATT. Another option is to wrap the audio data into vendor-specific HID profile service. The latter is preferred by those who are familiar with writing vendor specific HID report handlers. The performance is equal between the two options. The first byte in each of the following tables, Protocol ID, is only valid for RF4CE. Table 6. Start Frame Number of Bytes

1 CMD ID

Field

0x04

Table 7. BLE ADPCM Data Frame Part #1/5 Frame Number of Bytes Field

1 Seq No

ID

[7:3]

[2:0]

0-31

0x01

1

1

1

16

Header 1

Header 2

Header 3

Audio Samples

Table 8. BLE ADPCM Data Frame Part #2/5 Frame Number of Bytes Field

20 Audio Sample

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Table 9. BLE ADPCM Data Frame Part #3/5 Frame Number of Bytes Field

20 Audio Sample

Table 10. BLE ADPCM Data Frame Part #4/5 Frame Number of Bytes Field

20 Audio Sample

Table 11. BLE ADPCM Data Frame Part #5/5 Frame Number of Bytes Field

20 Audio Sample

Table 12. Stop Frame Number of Bytes Field

6

1 CMD ID 0x00

Voice Over Remote Control

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1.2.4

Sequence Diagram Audio Protocol Controller

Application

USER

BLE RF4CE

Target

Stack

Application

Stack

³3XVK $XGLR .H\´ Reset, configure and start audio codec

Data Frame/ Connection Event

Send 1st Start Cmd Data Cnf

Data Cnf

Data Indication/ Notification

Initialize Audio

Disable Frequency Aglity

nd

Send 2 Start Cmd (confirm channel) Data Cnf

RF4CE only Data Frame Data Cnf

Data Indication

Start Buffering Audio Frame Frame ready to be sent in audio queue

³5HOHDVH $XGLR .H\´

Send Data Request, Audio Data Frame

Data Frame / Connection Event Notification Notification

Data Indication Notification Notification

Decode frame, play audio on speaker, mic or file.

Stop Codec, empty queue. Send Data Request, Audio Stop Frame Data Frame/ Connection Event

Data Indication/ Notification

Stop Audio

Enable Frequency agility

RF4CE only

Figure 6. Sequence Diagram

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