On 10/09/2012 02:21 PM, Clemens Ladisch wrote:
The three possibilities to store little-endian signed 24-bit samples in memory are (where L=LSB, M=MSB):
0padding LLLLLLLL MMMMMMMM HHHHHHHH S32_LE LLLLLLLL MMMMMMMM HHHHHHHH 0padding S24_LE LLLLLLLL MMMMMMMM HHHHHHHH S24_3LE
The first two require the DMA controller to transfer four bytes, the last one, three bytes.
All three use (at least) 24 bits on the wire.
Oh, I always assumed that S32_LE was just a 32-bit format. That's what I've been assuming so far, and the resulting data files from "arecord -f {S32_LE|S24_LE|S24_3LE}" were perfectly understood by audio programs. Basically, what you're claiming here is that S24_LE must store the audio data in the lower 3 bytes? Because in my experiments so far I concluded I had to fill the high order bits for both S24_LE and S32_LE formats.
Hence Mike would be right that S24_LE has to use a 4-byte dma transfer size, no?
Yes.
It's not strictly what I wrote, but it's what I meant, yes.
Now we're on the topic of DMA controllers: When reading multiple channels (e.g. 2 or more codecs on the serializers either using TDM or multiple AXR pins), the DMA controller must always read 32 bits per sample from the serializer, regardless of the sample format used. Currently I implement this by enforcing S32_LE or S24_LE formats, and denying all others when multiple serializers are involved. Would it be possible to instruct the davinci's DMA controller to read 32 bits but write only 8, 16 or 24 bits to memory for each sample?
Met vriendelijke groet / kind regards,
Mike Looijmans
TOPIC Embedded Systems Eindhovenseweg 32-C, NL-5683 KH Best Postbus 440, NL-5680 AK Best Telefoon: (+31) – (0)499 - 33.69.79 Telefax: (+31) - (0)499 - 33.69.70 E-mail: mike.looijmans@topic.nl Website: www.topic.nl
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