Linux audio for smartphones
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The document discusses the evolution of audio subsystems in smartphones, highlighting the transition from traditional embedded operating systems to the Linux ASOC audio framework. It emphasizes the benefits of the Linux solution, including reusable drivers, dynamic audio power management, and improved application integration. Future directions for smartphone audio technology are also outlined, featuring advanced features such as noise cancellation and better system calibration.
Linux audio for smartphones
- 1. Linux Audio for Smartphones A b i f i t d tiA brief introduction www.wolfsonmicro.com1 April 2011© 2011 Wolfson Microelectronics plc
- 2. Overview • Modern smartphone audio subsystems di i l b dd d l i• Traditional embedded OS solutions • ASoC – the Linux solution D i i• Design overview • Brief introduction to chip drivers • Walk through of system audio driver construction• Walk through of system audio driver construction • Future directions www.wolfsonmicro.com2 © 2011 Wolfson Microelectronics plc April 2011
- 3. Modern smartphone audio subsystems HDMI CPU Mixing Earpiece Speaker CPU Mixing Headset Dock Bluetooth Cellular dmodem www.wolfsonmicro.com3 April 2011© 2011 Wolfson Microelectronics plc
- 6. Traditional software driver model Memory Processing OutputMemory Processing Output www.wolfsonmicro.com6 © 2011 Wolfson Microelectronics plc April 2011
- 7. Traditional software model • Monolithic driver for entire subsystem • N t t f i ff CPU h d• No structure for managing off‐CPU hardware • Very little reuse • Detailed register level knowledge of componentsDetailed register level knowledge of components • Time consuming • Tight coupling between application and kernel codeTight coupling between application and kernel code www.wolfsonmicro.com7 © 2011 Wolfson Microelectronics plc April 2011
- 8. The Linux solution • ASoC embedded audio framework • P id t d d ALSA i t f t li ti• Provides standard ALSA interface to applications • Merged since 2.6.21, April 2007 • Reusable drivers for each chipReusable drivers for each chip • CPU audio interface, DMA controller and “CODEC” • Minimal per‐system drivers linking themMinimal per system drivers linking them • Automatic and transparent power management • Configuration done by applicationsConfiguration done by applications • Allows interactive tuning of system • Keeps flexibility for application layer • More reuse, less coupling www.wolfsonmicro.com8 © 2011 Wolfson Microelectronics plc April 2011
- 9. Dynamic Audio Power Management • Looks for audio paths connecting inputs to outputs l i i h• Powers only components in an active path • Automatically activates DACs and ADCs DAC Speaker Mixer FM radio Headset www.wolfsonmicro.com9 © 2011 Wolfson Microelectronics plc April 2011
- 10. ASoC CODEC driver • Four classes of control • A di i t l ( l ff t )• Audio processing controls (eg, volume, effects) • Audio routing controls (DAPM controls and routes) • Power controls (DAPM widgets, bias)Power controls (DAPM widgets, bias) • Stream control (Digital audio streaming) • Mostly direct mapping into register mapy pp g g p • SOC_DOUBLE_R_TLV("DAC1 Volume", WM8994_DAC1_LEFT_VOLUME, WM8994_DAC1_RIGHT_VOLUME, 1, 96, 0, digital_tlv), www.wolfsonmicro.com10 © 2011 Wolfson Microelectronics plc April 2011
- 11. Application layer integration • CPU audio stream management provided by the OS • A di Fli P l A di• AudioFlinger or PulseAudio • Determine and apply use case • Run external utilities simple but slow• Run external utilities – simple but slow • Call raw ALSA control APIs – maximum control, maximum effort • Apply settings with ALSA UCM – standard configuration file formatpp y g g • Stream audio • ALSA PCM API www.wolfsonmicro.com11 © 2011 Wolfson Microelectronics plc April 2011
- 12. System integration walkthrough “Baseband” Headset Speaker S3C6410 WM8996 CODEC Mics WM9081 Amplifier Subwoofer http://opensource.wolfsonmicro.com/content/speyside‐audio p http://opensource.wolfsonmicro.com/content/speyside audio www.wolfsonmicro.com12 © 2011 Wolfson Microelectronics plc April 2011
- 13. Future directions • Nicer handling of digital basebands f• Greater use of DSP • Enhanced features – ambient noise cancellation, beam forming, echo cancellation, offloaded decompression, speaker compensationecho cancellation, offloaded decompression, speaker compensation • Even more dynamic reconfiguration of the audio subsystem • Coefficient management and in‐system calibrationg y • Use case development and management • Greater adoption of UCM • User interfaces for configuration development • ASoC conference, 4th‐5th May • http://www.slimlogic.co.uk/?p=268 www.wolfsonmicro.com13 © 2011 Wolfson Microelectronics plc April 2011