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Today's Featured Head-Fi Blog: A Japanese headfier's monologue (Sasaki)
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Yes. First of all, USB has 'host' and 'peripheral' devices. The host is responsible for mediating the bus and there must be exactly one on each bus (it's also responsible for providing power).
<Snip>
It's probably possible for a USB host stack to be written for RockBox or iPod Linux (the PortalPlayer CPU in the iPod has a USB port that can be either a host or device) that could potentially allow connection of a USB audio class device for audio playback. You're welcome to try - but tapping the I2S lines is sure to be much simpler. This would be pretty cool though.
Thanks for all of the info. That was massively helpful and what I was looking for from the start.
Two things I did pick up from that are:
1) Re: USB power - I think I found a flaw in the IS2 direct connection approach. The Pico DAC is powered by USB and not by the included battery (this powers the amp section only). Therefore to use the DAC you would need to have the Pico also plugged into a powered USB source/host. Other then cramping the portability, this may also impact functionality (unless it would still work with no audio signal being received from the USB host, just the power).
2) If it is possible to write a hoststack for Rockbox this does sound like the preferable option. I don't think it would be any "harder", it would just require different skills. The advantage to this would also be that is infinitely replicable with minimal effort on all users part (all they have to do is install the new firmware). Also re: power, the Pico would then be drawing power from your iPod and as such this would reduce battery times.
In conclusion I would love for someone to investigate the option of performing a firmware modification that would allow this kind of interaction
This thread also happens to coincide with the annoucement of the iPhone SDK. Perhaps an application could also be developed to enable this function on the iPhone
1) Re: USB power - I think I found a flaw in the IS2 direct connection approach. The Pico DAC is powered by USB and not by the included battery (this powers the amp section only). Therefore to use the DAC you would need to have the Pico also plugged into a powered USB source/host. Other then cramping the portability, this may also impact functionality (unless it would still work with no audio signal being received from the USB host, just the power).
For that, you would just make a USB cord that doesn't connect D+ and D-. After that, you'd have to wonder why portability is such a hassle. You'd have to wonder if the chips chosen for the iPod are all that bad and if it's worth the trouble replacing them. Looking at the project from the end result, it seems like it's not all that bad; wire this here and there, wire that there and here. Make your own USB cable, get on what seems to be some kind of donor transplant list to get a Headamp Pico (donor transplant list because it's long, not because Justin isn't doing a great job with what he has to deal with), wire up your iPod's silly small chip to more silly small pads. Are we forcing a cube into a circular hole?
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