ALSA音频驱动源代码

Advanced Linux Sound Architecture - Driver Jaroslav Kysela <perex@suse.cz> v0.0.1, 12 May 1998 This document describes, in full detail, the Advanced Linux Sound Architecture driver. ______________________________________________________________________ Table of Contents 1. Introduction 1.1 Source files 1.2 Devices 1.3 Memory allocation 1.4 Basic coding 1.5 Upper level (/cards) 1.6 Private data/values 1.7 CLI/STI & spin locking 1.8 Examples 2. Soundcard 2.1 Variables and functions 2.1.1 Examples 2.2 Resources 2.2.1 Examples 2.3 ISA DMA 2.4 PCI bus 2.4.1 Examples 3. File operations 3.1 Variables and functions 3.2 Examples 4. Mixer 4.1 Variables and functions 4.2 Exaples 5. PCM - Digital Audio 5.1 Variables and functions 5.2 Examples ______________________________________________________________________ 11.. IInnttrroodduuccttiioonn This document describes the ALSA driver and kernel API. Application programmers should use the library API rather than kernel API. The ALSA Library offers 100% of the functionally of the kernel API, but add next major improvements in usability, making the application code simpler and better looking. In addition, some of the some fixes/compatibility code in, may be placed in the library code instead of the kernel driver. 11..11.. SSoouurrccee ffiilleess Source files are separated to: //iinncclluuddee Directory contains all header files which are included from more sources. //kkeerrnneell Directory with kernel code and abstract layers (middle level code and library). //lloowwlleevveell Generic lowlevel code for chip(set)s. //ccaarrddss Upper level for soundcards and specific lowlevel code. //ddeetteecctt Detection layer (_/_p_r_o_c_/_a_s_o_u_n_d_/_d_e_t_e_c_t - to make installation easy). 11..22.. DDeevviicceess Devices should use abstract code from sound kernel, but it should use own code and register minors separetely (with snd_minor_register and snd_minor_unregister functions). This method totaly bypass all abstract code, so code for these soundcards must handle all things. 11..33.. MMeemmoorryy aallllooccaattiioonn +o vvooiidd **ssnndd__mmaalllloocc(( uunnssiiggnneedd lloonngg ssiizzee )) +o vvooiidd ssnndd__ffrreeee(( vvooiidd **ppttrr,, uunnssiiggnneedd lloonngg ssiizzee )) +o cchhaarr **ssnndd__mmaalllloocc__ssttrrdduupp(( cchhaarr **ssttrriinngg )) +o vvooiidd ssnndd__ffrreeee__ssttrr(( cchhaarr **ssttrriinngg )) These routines use their own memory allocation algoritm. It should be removed in the future and replaced with kmalloc and kfree calls, but for now I need to trace all allocation problems to make code clean... Note: ALSA driver heavily uses dynamic allocation for most things. For debugging you should use command './configure --with-debug=full' for configuration. This enables trace of allocated memory with above functions and this makes debugging a little bit easier. 11..44.. BBaassiicc ccooddiinngg All things are made as objects (which encapsulates data and functions) and are referenced in this way. I don't prefer to pass index to some array of structure or something like this. Objects contain both data and functions. Pointers to these objects are passed around (like C++). All main structures should have snd_xxxx_new, snd_xxxx_free, snd_xxxx_register, snd_xxxx_unregister functions. +o ssnndd__ccaarrdd__tt is a basic structure which contains info about a soundcard, index and resource tracking variables. Look at _i_n_c_l_u_d_e_/_d_r_i_v_e_r_._h for all things related to this structure. +o ssnndd__ppccmm__tt is a basic structure for a PCM device. +o ssnndd__ppccmm__cchhaannnneell__tt is a basic structure for a PCM channel (direction). +o ssttrruucctt ssnndd__ssttrruu__ppccmm__hhaarrddwwaarree is a structure which must be filled by lowlevel code. Look at _i_n_c_l_u_d_e_/_p_c_m_._h for all things related to these structures. +o ssnndd__kkmmiixxeerr__tt is a basic structure for a MIXER device. +o ssnndd__kkmmiixxeerr__cchhaannnneell__tt is a basic structure for a MIXER channel. +o ssttrruucctt ssnndd__ssttrruu__mmiixxeerr__cchhaannnneell__hhww is a structure which must be filled by lowlevel code. Look at _i_n_c_l_u_d_e_/_m_i_x_e_r_._h for all things related to these structures. 11..55.. UUppppeerr lleevveell ((//ccaarrddss)) Code for soundcards should contain these things: 1. Support for more than one of the same soundcard (up to SND_CARDS)... +o it isn't really possible due to HW limitations 2. Autodetection/autoconfiguration feature (if it's possible)... +o if lowlevel code is specific for soundcard type - it should be here, too.. 3. Initialization code for soundcard +o snd_card_new +o snd_card_free (frees all hardware resources) 4. Allocate/free hardware resources for soundcard +o snd_register_ioport +o snd_unregister_ioports (frees all ioports) +o snd_register_interrupt +o snd_unregister_interrupts (frees all interrupts) +o snd_register_dma_channel +o snd_unregister_dma_channels (frees all DMA channels) 5. Initialize other layers (PCMs, Mixers etc.) +o snd_pcm_new +o snd_pcm_free +o snd_pcm_register +o snd_pcm_unregister (calls snd_pcm_free) +o snd_mixer_new +o snd_mixer_free +o snd_mixer_register +o snd_mixer_unregister (calls snd_mixer_free) 6. Register soundcard +o snd_card_register +o snd_card_unregister (doesn't call snd_card_free) NNoottee:: Due to module dependency you should separate code for soundcards from the same manufacture which have slightly different hardware. Example: The GUS Extreme has an ESS ES-1688 chip. This chip isn't in the GUS Classic. For GUS Classic, the generic code in the snd-es1688.o module isn't needed. So there are two upper level modules (snd- gusextreme.o and snd-gusclassic.o). 11..66.. PPrriivvaattee ddaattaa//vvaalluueess Some structures have pointers to private data and values. These variables aren't used with the abstract layers and are intended for low-level code use only. ______________________________________________________________________ snd_card_t -> private_data snd_card_t -> private_free (called from snd_card_free if not NULL) ______________________________________________________________________ ______________________________________________________________________ struct snd_stru_pcm_hardware -> private_data struct snd_stru_pcm_hardware -> private_free (called from snd_pcm_free if not NULL) snd_pcm_t -> private_data snd_pcm_t -> private_free (called from snd_pcm_free if not NULL) ______________________________________________________________________ ______________________________________________________________________ struct snd_stru_mixer_channel_hw -> private_value snd_kmixer_channel_t -> private_data snd_kmixer_channel_t -> private_free (called from snd_mixer_free if not NULL) snd_kmixer_t -> private_value snd_kmixer_t -> private_data snd_kmixer_t -> private_free (called from snd_mixer_free if not NULL) _______________________________________________________