On Friday 10 April 2009 08:48, Jorge Pinto aka Casainho wrote:

> Hello :-)
>
> As I said before, we are working on Lyre project, a Free/Open hardware
> audio player (DAP) and recorder, for use with RockBox firmware.
>
> We will probably use an SD Card for hold the audio files and for easy
> the life of users for sharing music (I mean music with Creative Commons
> license and the recorded by users).
>
> My question is: is the USB really need if we have an SD Card? would
> users still miss the USB?

Yes.

People are very familiar with using USB mass storage devices, every computer
these days has USB sockets, whereas only some have SD card slots, and USB
cables are much more straighforward than fiddling around with inserting &
removing SD cards from devices.

> 2nd question: if we need to use USB, does we need to pay royalties for
> use it?

I have no idea about this aspect of things.

> I think we will need USB for an easy way to flash the Rockbox bootloader
> + firmware on internal flash player memory..

You could achieve this requirement by putting a specially-named file on an SD
card and starting the machine with the SD card inserted, so it recognises the
file and does whatever it would have done with a file arriving by USB.

However, USB is so much more convenient that I think it should be regarded as
an essential part of the spec for such a project.

Bear in mind that many flash-based MP3 players have an integrated USB plug,
and the ones which also have an SD card slot often present this device as a
second drive/partition on the USB connector - therefore people are familiar
with talking to the SD card through the USB plug, which I suspect is used far
more often than removing the SD card and connecting that to the computer by
another means.

Personally I would regard USB as the way to talk to the device, and SD as a
way of expanding its storage capacity, but once an SD card it inserted, it
would very seldom be removed.

Regards,

Antony.

-- 
"The problem with television is that the people must sit and keep their eyes 
glued on a screen; the average American family hasn't time for it."
 - New York Times, following a demonstration at the 1939 World's Fair.
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