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Subject: Re: WAV Codec for Archos

Re: WAV Codec for Archos

From: Christoph Niedeggen <Niedeggen_at_gmx.net>
Date: 2006-01-25

>> It's a shortcoming of the serial interface. It streams the
>> bits in UART order (LSB first), but internal serial interfaces
>> are SPI, which is MSB first. Since the order can't be
>> programmed, we have to twist every byte, can't DMA it
>> directly.
>
> This is only true for playback, as the CPU is hooked to the
> MAS serial input. Recording uses a parallel interface, so no
> bitswap necessary.
>
>> A similar problem exists for the disk I/O, here we have to
>> endian swap byte pairs. Archos unfortunately wired the 16 bit
>> data bus directly 1:1, not taking into account that IDE is
>> little endian and the SH CPU is big endian.
>
> Not a big issue though; the asm-optimised routines transfer
> ~4MB/sec. :-)

> Fortunately rockbox uses DMA for these serial transfers, and
> we can drop the double bitswap if we make special provisions
> in the filesystem and MMC driver

So from your point of view the CPU should be able to manage everything
necessary for playing back and recording PCM data in the standard WAV
format? That would be great!

Did you do some testing with the codec yet, Jens? What are your results?

Regards
Christoph
Received on Thu Jan 26 00:04:43 2006


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