i.mx audio interfaces - freescale semiconductor

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Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2009.

i.MX Audio Interfaces

Mithra Weerakoon and John ScottApplications Engineers with the Multimedia Applications Division

July 14, 2009

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2Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2009.

What audio interfaces are in i.MX processors?

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What is covered in today’s presentation?

►Today, we are going to talk about the audio interfaces available

in the i.MX processor family.

►They are as follows:•

ESAI –

Enhanced Serial Audio Interface (John)•

SSI –

Synchronous Serial Interface (Mithra)•

AUDMUX –

Digital Audio Multiplex (Mithra)•

SPDIF –

Sony/Philips Digital Interface (John)•

ASRC –

Asynchronous Sample Rate Converter (John)•

MLB –

Media Local Bus (Mithra)►We will also touch on Audio Clock Routing and give our

recommendations on how to get the best audio performance in your system.

►We will end with a block diagram of a typical system using i.MX.

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The Enhanced Audio Serial Interface (ESAI)

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What is the ESAI used for?

►Primarily used to provide an interface between an audio source and the i.MX processor

►Source could be via an external codec (e.g. ADC) or external SPDIF receiver

►Also provides the data on the back-end, e.g. can supply the DAC which drives the loudspeaker or Digital Amplifier directly

►Optimized for multichannel support in supplying the i.MX processor (large FIFOs)

►Can handle high sample rates, e.g. up to 192kHz►Uses either an optical (Toslink) or co-ax (RCA) cable from device to

i.MX processor

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ESAI Features

►Independent (asynchronous mode) or shared (synchronous mode) Tx

and Rx sections with shared or separate int/ext clocks and frame

synchs, operating in master or slave modes►Supports many digital audio industry standards including I2S and

AC97 modes►Two dedicated TX pins and four selectable TX/RX pins►TDM network mode compatible►Up to 32 words per period in network mode►Input clock source can be system clock (not recommended) or

external oscillator, or use slave mode►Programmable internal clock divider and frame sync generation►128 word transmit FIFO shared by transmitters►128 word receive FIFO shared by receivers

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ESAI Peripheral

TX5Shift Register

RX0

TX2Shift Register

RX3TX3

Shift Register

RX2TX4

Shift Register

RX1

TX1Shift Register

TX0Shift Register

RSMARSMB

TSMATSMB

RCCRRCR

TCCRTCR

SAICR

SAISR

TSR

Clock/Frame SyncGenerators

andControl Logic

DD

B

GD

B

SDO0 [PC11]

SDO1 [PC10][P

C3]

SC

KT

[PC

4] F

ST

[PC

5] H

CK

T

[PC

1] F

SR

SDO2/SDI3 [PC9]

SDO3/SDI2 [PC8]

SDO4/SDI1 [PC7]

SDO5/SDI0 [PC6]

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The Synchronous Serial Interface (SSI)

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SSI Overview

►SSI is a full duplex serial interface that enables the chip to communicate with a variety of serial audio devices.

►These devices can be standard AD/DA converters or digital signal processors used for audio post processing (for example).

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SSI Features

►Independent transmit and receive sections

►Data clocks for the port can be internally as master or externally generated as slave*1 device

►Programmable data interface modes such as I2S, LSB, MSB aligned, and AC97 support

►Programmable word length (8, 10, 12, 16, 18, 20, 22 or 24 bits)

►Program options for frame sync and clock generation

►SSI power-down feature

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SSI Block Diagram

TMFreescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2009.

Digital Audio Multiplexer (AUDMUX)

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Digital Audio Multiplexer Features

►The Digital Audio Multiplexer (AUDMUX) enables interconnection of the two SSI interface ports to external audio devices. The data and clock signals from the SSI interface ports are always routed to the external devices via the AUDMUX.

►Total of 7 Muxers

are provided

►Three internal ports and four external ports

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Digital Audio Multiplexer Features

►Three internal ports►Four external ports►Full 6-wire SSI interfaces for asynchronous receive and transmit►Configurable 4-wire (synchronous) or 6-wire (asynchronous)

peripheral interfaces►Independent Tx/Rx frame sync and clock direction selection for host

or peripheral►Each host interface’s capability to connect to any other host or

peripheral interface in a point-to-point or point-to-multipoint (network mode)

►Transmit and receive data switching to support external network mode

►CE Bus network mode to provide synchronous switching on RxD

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Digital Audio Multiplexer Block

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The Sony/Philips Digital Interface (SPDIF)

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What is the SPDIF used for?

►Common interface used in digital audio e.g. digital output for CD players and DVD/Blu-ray players

►Can transmit uncompressed (e.g. PCM) or compressed (e.g. Dolby Digital, DTS) data

►Easy way to get stereo or multichannel audio into the i.MX processor

►Avoids the need for an external SPDIF Rx chip if integrated into

the i.MX processor (around $1 BOM cost)

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SPDIF Features

►Full SPDIF receiver and transmitter available in i.MX35►SPDIF transmitter only available in i.MX37 and i.MX51►1 input (i.MX35 only) pin and 1 output pin►16 channel FIFO data buffer►Can handle both Channel Status (CS) and User (U) data►Includes frequency measurement block for accurate measurement

of incoming sampling frequency►Supports bypass mode of SPDIF in > SPDIF out (i.MX35 only)►Supports IEC958 biphase

mark format (data, CS and U bits)

►Both Tx

and Rx clocks are sent to the ASRC

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SPDIF Rx/Tx Block DiagramSPDIFIN only on i.MX35x

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The Asynchronous Sample Rate Converter

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What is the ASRC used for?

►Allows audio sample rate conversion between sources with independent clock domains, e.g. 44.1kHz audio from CD and 8kHz audio from Bluetooth®

►Can provide a fixed sample rate output, e.g. 48kHz audio output for additional processing or playback

►Can be used for up-conversion of audio, e.g. 48kHz input up- converted to 96kHz output

►Can be used for down-conversion of audio, e.g. 96kHz input down- converted to 48kHz output

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Asynchronous Sample Rate Convertor (ASRC) Features

►Hardware co-processor requiring minimal CPU intervention (i.e. low MIPS)

►Support ratio range of between 1/24 to 8 (Fs in to out)►Up to 10 channel simultaneous conversion►Supports simultaneous conversion in up to 3 sample rates►Typical performance of -120dB THD+N►Dynamic range of 144dB►Designed for conversion between: 32kHz, 44.1kHz, 48kHz and

96kHz►Can support 8kHz to 32kHz as well with less performance (values?)►Clock inputs may by sourced from SSI Rx, ESAI Rx, S/PDIF Rx or

PLL►Clock outputs may drive the SSI Tx, ESAI Tx

or S/PDIF Tx

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(MLB)

Media Local Bus Device Interface Macro

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What is the MLB used for?

►Implements the required functionality of a media local bus (MLB) device. This logic serves as an interface between the MLB and a

customer IC, implementing the Physical-

and Link-Layer requirements outlined in the MediaLB

Specification.

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MLB Features

►Transmission of commands and data when functioning as the transmitting device associated with a Channel Address

►Reception of data and transmission of RxStatus

responses when functioning as the receiving device associated with a Channel Address

►MediaLB

lock detection

►System channel command handling

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Audio Clock Routing

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Audio Clock Routing Options

►i.MX processor configured as clock slave where audio data clocks are sent from another device

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►i.MX processor configured as clock Master and, •

Audio clock derived from the internal PLL of the i.MX

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►i.MX configured as clock Master and, •

Audio clock derived from the dedicated external crystal/oscillator

i.mx processor AD/DA converter

Audio clocks

Audio data

Dedicated audioclock

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Effects of Audio Clocking Methods

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Audio Performance

►The internal DPLL on the i.MX processor is not best suited for clocking audio peripherals. Use of the i.MX processor master mode using the internal PLL may yield degraded audio performance for some applications.

►Measured jitter on the audio master clock when the internal PLL is sourced as clock is approximately 800 ps.

►Measured jitter on the audio master clock with the dedicated external audio crystal is approximately 55 ps.

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Audio Performance

►Audio clock jitter vs. frequency when internal PLL is used as clock source

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Audio Performance

►Audio clock jitter vs. frequency when internal dedicated audio crystal used as clock source

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Audio Performance

►FFT plot for the case when internal PLL is used for clock mastering.

Elevated noise due

to clock jitter

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Audio Performance

►FFT plot for the case when an external dedicated crystal is used for clock mastering

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Audio Performance

►Noise at the fundamental and the 2nd harmonic frequency is greater when the internal PLL is used for audio clocks.

►Jitter performance is better when dedicated audio crystal is used.

►Depending on the application, either approach can be used. It is recommended to avoid use of the internal PLL as an audio clock

source on applications that call for best audio sound quality performance.

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Typical Audio System Block

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Audio System Block

►ESAI for main audio out channels and a stereo auxiliary input.

►Two SSI ports can be used for GPS and the Bluetooth®

module.

►Audio Clocks can be slave or master, depending on the application.

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i.MX Part’s Audio Features

Feature/Part i.MX23x i.MX25x i.MX27x i.MX31x i.MX35x i.MX37x i.MX51x

ESAI NO YES NO NO YES NO NO

SSI YES YES YES YES YES YES YES

ASRC NO NO NO NO YES NO NO

SDPIF YES (TX only) NO NO NO YES YES (TX only) YES (TX only)

Audio MUX YES YES YES YES YES YES YES

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Wrap up

►Today, we talked about the audio interfaces available in the i.MX processor family.

►We also spoke about Audio Clock Routing and explained how to get the best audio performance in an i.MX processor-based system.

►We showed a typical block diagram of the audio based portions of

a possible i.MX system.

►And we explained which i.MX processors have which audio peripherals.

►For more details, please contact your local Freescale sales representative or go to www.Freescale.com

http://www.freescale.com/

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Q&A

►Thank you for attending this presentation. We’ll now take a few moments to review the audience questions, and then we’ll begin the question and answer session.

i.mx audio interfaces - freescale semiconductor

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