Do you mean that there is no test program to verify the implementation is correct ?
Some sound card 's hardware has FIFO buffer.
For example , au88x0
according to patent 6167465
Additionally, a first-in-first-out (FIFO) buffer is established for the DMA channel. Then a DMA request is generated in order to begin filling the FIFO buffer with data from the first data segment 150(0) using the information provided by CPU 210.
The FIFO buffer may be any suitable size capable of handling bus latencies while small enough such that the memory requirement is not overly burdensome. In one embodiment of the present invention, the FIFO buffer is 32 samples or words in depth, which would withstand a maximum bus latency of about 4 microseconds. By way of example, if 48 DMA channels trigger simultaneously, with a trigger level set at half the buffer size (16 samples), each DMA channel can wait 16 samples (20 microseconds per sample), or approximately 320 microseconds before running out of data.
It seem that alsa-lib should not allow application to rewind the application pointer to hardware pointer since you cannot write the next sample because of FIFO buffer even using mmap read/write
or bug in *snd_pcm_rewindable() ?*
2009/9/24 Takashi Iwai tiwai@suse.de
At Thu, 24 Sep 2009 13:04:24 +0530, Anuj Aggarwal wrote:
Hi,
I want to try the forward/rewind APIs supported by the ALSA library. Can someone point to an ALSA application which exercises these APIs?
Pulseaudio is using snd_pcm_rewind(). About snd_pcm_forward(), I don't know of...
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