Hardware Background ------------------- ABE (Audio back end) IP on the OMAP4 SoC of TI provides digital audio signal processing features (real-time mixing, equalization, etc) on the media processor. ABE allows flexible routing of the audio paths with dedicated equalizer and acoustics protection for earphone/ headphone, hands-free and vibra paths. Typically the ABE is connected to a companion analog audio chip via a dedicated McPDM (multi-channel pulse density modulation) as show at
http://dev.omapzoom.org/?p=misael/kernel-audio.git;a=blob;f=sound/soc/codecs... ;
Proposal -------- On OMAP4, audio codec functionality is spread between ABE of OMAP4 and the companion analog audio chip. The interface between the ABE and Phoenix audio chip is proprietary McPDM interface. The proposal is to combine both ABE and Phoenix into a codec driver. OMAP4 ABE also provides other links for routing digital processed data to McBSP, McASP interfaces, which are at the same level as McPDM interface.
+---------+ +---------------------+ ALSA Library --|ASOC Core|--|OMAP4 Platform Driver| +---------+ +---------------------+ | <DMA-DAI> | +-----------------------+ |ABE--<McPDM>--Phoenix--|--o Speaker/MIC +-----------------------+
ABE provides a FIFO interface (similar to McBSP FIFO) and the audio data transfer between the audio buffers and ABE FIFO is handled through the CPU DAI. Handling of the McPDM interface between the digital audio (ABE) and analog audio chip (Phoenix) is handled internally in the codec driver as part of the codec DAI operations.
This RFC addresses the basic audio usecases using Phoenix companion chip with the OMAP4 audio IP block. Support and configuration for using different codecs (connectivity with BT/FM etc) using I2S/PCM interfaces are targeted for future enhancements.
High Level Design ----------------- Following are the files consisting of the TI OMAP4 audio driver:
sound/soc/omap/omap-pcm.c: This is the platform driver for OMAP audio. It remains the same across all OMAP chip versions.
sound/soc/codecs/abe-twl6030.c: This is the codec driver interface file for OMAP4 audio. It defines the codec DAIs for the HIFI, voice and Vibra subdevices. Handles the configuration of Phoenix companion chip using i2c control interface. Handles the initialization and configuration of ABE. All codec related widget controls are also handled in this file. Both, digital (ABE) and analog (twl6030) widgets will be contained in this same driver.
sound/soc/codecs/abe/*: This folder contains the ABE specific handlers. i.e reset, clock, configuration of ABE ports for different stream inputs/outputs etc.
sound/soc/omap/oma-abe.c: This is the DAI driver towards the abe.
sound/soc/omap/sdp4430.c: This is the machine driver for SDP4430 and defines the stream connections.
Questions --------- How to handle routing of digital audio from ABE to external devices like Bluetooth/FM connectivity devices which are usually connected using McBSP interfaces?. In these scenarios, we need another DAI between the ABE (platform codec) and an external codec.
ABE(platform Codec (Digital) -----> Phoenix audio codec | | +--> BT/FM codec