Takashi Iwai wrote: >At 04 Apr 2002 15:41:36 +0200, >Leif Lindholm wrote: > >>Hello >> >>I'm working on a set-top-box based on the National Semiconductor SC1200 >>Geode integrated microprocessor. >> >>National have been nice enough to write an Alsa-driver for the built-in >>AC97-controller/audio thingy - unfortunetaly it is written for 0.5.10b. >> >>So now I need to modify this one to use with 0.9. >> >>Can someone give me a few tips/hints or is there possibly a document >>about this that I failed to google up? >> > >unfortunatley (as always :) there is no documentation about the kernel >stuff yet. >since you have already a working 0.5.x driver, it's not too difficult, >though. > >as far as i can remember.. > >- renaming > > fragment -> period > channel -> stream > voice -> channel > snd_pcm_subchannel -> snd_pcm_substream > >- renaming of constants > > generally: > SND_XXX -> SNDRV_XXX > > some other changes, too: e.g. > SND_PCM_TRIGGER_GO -> SNDDRV_PCM_TRIGGER_START > >- snd_assert() is used instead of snd_debug_check() > (note that the argument is opposite, assert(x) means that "x" is true .) > >- no longer difference of stream/blocking modes > >- general hardware information is stored in snd_pcm_hardware_t > and passed to the runtime struct in open(). > the information is intuitive, look at other sources. > >- abstracted ops. > > open(substream) > - open the device > - copy the substream->runtime->hw parameter > (not pass the pointer) > - set up the constraints (if any) > > hw_params(substream, hw_params) > - allocate a buffer > usually via snd_pcm_lib_malloc_pages > > prepare(substream) > - set up the hardware parameters (like 0.5.x) > > note that parameters in runtime struct are > stored in frames, not in bytes. > there are functions, snd_pcm_lib_buffer_bytes() > and snd_pcm_lib_period_bytes() > > trigger(substream, cmd) > - start, stop, pause (like 0.5.x) > > pointer(substream) > - returns the current pointer where the hw refers. > (in frames!) > > hw_free(substream) > - free the buffer > usually via snd_pcm_lib_free_pages(substream) > > close(substream) > - close the device, clean up. > > copy, silence > - needed only if you don't (can't) use mmap. > > they are defiend in snd_pcm_ops_t struct and set up in > pcm initizliation routine via snd_pcm_set_ops(). > >- when the interrupt occurs at period (fragment), call > > snd_pcm_period_elapsed(substream) > > just once per interrupt. > >- no longer snd-xxx functions for allocating port, dma and irqs. > you need to use standard functions. > for releasing struct resources *, you have to use kfree_nocheck() > to avoid malloc-wrapper. > >- definitions of pci id table, probe(), remove() (suspend() and > remove() if possible) on struct pci_driver. > >- finally and best way - look at drivers on a same chip of both 0.5.x > and 0.9.0, and compare them :) > > > >Takashi > This is a very good start at some documentation!
In case Leif does not understand the concept of a frame, here is what I understand by it. Audio stream is 16 bit samples, 2 channels = 4 bytes (2 bytes of each sample, and 2 channel=2*2) = 1 frame Audio stream is 16 bit samples, 6 channels = 12 bytes = 1 frame Audio stream is 8 bit samples, 2 channels = 2 bytes = 1 frame So, no matter what the sample bits, or number of channels, there is always 1 frame. If the stream is 48000 Hz, it will contain 48000 frames. If the stream is 44100 Hz, it will contain 44100 frames. If the stream is 48000 Hz, 16 bit samples, 6 channels 5.1(surround) audio, it will contain 48000 frames. Hopefully, by these examples, you get an idea of what a frame is. Cheers James _______________________________________________ Alsa-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/alsa-devel
