Em 16/7/2011 15:30, Jacopo Monegato escreveu:
> Hello,
> i hope the tag is correct. I was wondering about this for a while. a coup=
le of years ago i bought a portable speaker, with cable and ipod dock, powe=
red both via batteries and usb. I crossed my fingers and one day i linked t=
he speaker with my pc. nothing. only power... but why? Unfortunately i don'=
t know much about USB protocol, but since it is a serial port it shouldn't =
be hard to write a software that sends the sample... or calculate the PW fo=
r a "simulated" class D then send only the 1 and the zeros... am I mad o_O?=
??? because i haven't found anything yet and my old teacher told me "good l=
uck if you want to learn usb by yourself, it's very hard to find technical =
resources of any kind"
>
> Jacopo Monegato


It seems that you do not understand how USB is supposed to work.

USB is a packet oriented master/(multiple)slave bus/protocol. There are
addressing, error checking, control packets and so on.

First, each slave device must identify itself as belonging to a "device
class". The host must "slice" the data and send it in packets to the
slave. The slave must receive the packets, regroup the data and use it
as supposed.


So, your device must identify itself as some sort of "audio playback
class" and adhere to the established standards/protocols for that class.
Remember, it is not simply starting pushing PCM audio samples, there is
a lot of other control information flowing too.


Isaac

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