Linux audio for smartphones
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A brief introduction to the Linux audio stack for smartphones. Presented at ELC/Android Builders Summit 2011
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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