Uploaded byAnil Kumar Pugalia
Audio Drivers
The document discusses Linux audio drivers. It introduces the Linux audio subsystem, including the ALSA sound core in kernel space and its interfaces for user space applications. It describes the vertical components like the sound core and horizontal components like audio codec and controller drivers. It also covers porting an audio driver, which may involve changing pin assignments for standard codecs or implementing new codec drivers.
More Related Content
Audio Drivers
- 1. Audio Drivers © 2010Anil Kumar Pugalia <email@sarika-pugs.com> All Rights Reserved.
- 2. What to Expect? Introductionto Linux' Audio Subsystem Audio Vertical: Sound Core Audio Horizontal Putting them all together: Porting © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 2 All Rights Reserved.
- 3. Audio Subsystem ALSA conforming Apps User Space OSS conforming Apps (aplay, arecord, mplayer, ...) (rawplay, rawrec, ...) /dev/snd/pcmCXDYz, /proc/asound /dev/dsp, /dev/adsp, /dev/snd/controlCX, /sys/class/sound /dev/mixer, /dev/audio /dev/snd/timer OSS Emulation Layer (snd_pcm_oss, snd_mixer_oss) ALSA (Sound) Core Control Data Audio Codec Driver I2C Audio Controller Driver Kernel Space I2S Hardware Space MIC Audio Controller Audio Codec Speaker © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 3 All Rights Reserved.
- 4. ALSA Sound CardInterface Header: <linux/sound/core.h> Data Structure: struct snd_card APIs int snd_card_create(int idx, const char *id, struct module *module, int extra_size, struct snd_card **card_ret); int snd_card_register(struct snd_card *card); int snd_card_free(struct snd_card *card); Inverse of both the above © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 4 All Rights Reserved.
- 5. ALSA PCM Interface Header:<linux/sound/pcm.h> Data Structure struct snd_pcm struct snd_pcm_ops APIs int snd_pcm_new(struct snd_card *card, const char *id, int device, int playback_count, int capture_count, struct snd_pcm **rpcm); void snd_pcm_set_ops(struct snd_pcm * pcm, int direction, struct snd_pcm_ops *ops); int snd_pcm_lib_malloc_pages(struct snd_pcm_substream *substream, size_t size); // Typically used in hw_params int snd_pcm_lib_free_pages(struct snd_pcm_substream *substream); // Typically used in hw_free © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 5 All Rights Reserved.
- 6. struct pcm_ops int (*open)(structsnd_pcm_substream *substream); int (*close)(struct snd_pcm_substream *substream); int (*ioctl) /* Miscellaneous controls */ (struct snd_pcm_substream * substream, unsigned int cmd, void *arg); int (*hw_params) /* Set h/w params & allocate the buffer */ (struct snd_pcm_substream *substream, struct snd_pcm_hw_params *params); int (*hw_free) /* Free the buffer */ (struct snd_pcm_substream *substream); int (*prepare) /* Set audio parameters for transfer */ (struct snd_pcm_substream *substream); int (*trigger) /* Trigger the transfer */ (struct snd_pcm_substream *substream, int cmd); © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 6 All Rights Reserved.
- 7. ALSA Sound CardInterface Header: <linux/sound/control.h> Data Structure: struct snd_kcontrol_new APIs int snd_ctl_add(struct snd_card * card, struct snd_kcontrol * kcontrol); int snd_ctl_remove(struct snd_card * card, struct snd_kcontrol * kcontrol); © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 7 All Rights Reserved.
- 8. Porting a AudioDriver Standard Audio Codec Mostly involves changing pin assignments as per the Board Design New Audio Codec Complete Driver as per the preceeding discussions, need to be implemented © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 8 All Rights Reserved.
- 9. Browse some AudioDrivers ALSA driver examples: sound/ arm/aaci.c soc/soc-*.c {core, pcm, utils} Codec driver examples: sound/ arm/aaci.c soc/codecs/twl4030.c Browse & Discuss any © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 9 All Rights Reserved.
- 10. What all havewe learnt? Introduction to Linux' Audio Subsystem Audio Vertical ALSA Sound Core & its Programming I/f Audio Horizontal Audio Codec Driver Audio Controller Driver Putting them all together: Porting © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 10 All Rights Reserved.
- 11. Any Queries? © 2010Anil Kumar Pugalia <email@sarika-pugs.com> 11 All Rights Reserved.