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Subject: Re: archos as a cd changer

Re: archos as a cd changer

From: Fernando Birra <>
Date: Thu, 1 Apr 2004 12:29:41 +0100

Hi Jörg,

>"[IDC]Dragon" <> escreveu na mensagem
>Fernando Birra wrote:
>> I've started from the Alpine M-BUS plugin from Jörg and modified it to
>> interact with the IBUS used in BMW cars. So now, I have an Archos "CD
>> Changer" in my car...
>Did you succeed to do IBUS directly, or are you communicating to an
>controller via RS232?

Someone designed a bidirectional level shifter using just normal NPN
transistors and resistors. I can send you the schematic if you like. This
interface is capable of sinking all the current needed to bring the car bus
down to around 0V. We are still facing some reception/transmission errors
when the radio volume is loud. It is strange but the louder the volume the
more errors we get in the comunication. However, interfacing a notebook with
an RS232-IBUS interface gives us no problems. No reception errors. But we
can also see some transmission errors coming from the archos. So, if the
radio volume is low enough everything is ok. If we turn the volume up, the
archos starts seeing lots of parity errors. And sometimes it also fails to
I don't have a scope but Richard (the person that designed the circuit) will
probably take a look at this issue during the weekend.

I tried to modify the archos to have a full duplex uart but I faced a very
strange situation. I wired the wires to the line-in plug but I started
having noise in the comunication. I tested this at the simulated bus at home
and I couldn't make the trasmission to the archos reliable. Would I need to
cut the traces from the line-in plug to the audio input pins on the mixer
chip? The wires passed quite near some coils inside the archos. Could this
be the problem?

I finally decided to unsolder the wires from the line-in connector and the
PB10 pin started to behave as normal (noise free). I left the wires there
but no more reception errors at my simulated bus.

>If it's an external controller, I once "specified" and posted a command set
>and response format to issue commands to Rockbox and query information from
>it, using the remote pin as half-duplex RS232. The command set was done in
>way that it can co-exist with the Archos remote. So this could be the basis
>for "intelligent remote controls", like a car stereo interface. There are
>several people working on similar subject, for different radio brands. It
would be
>great if you can agree on a common command set, so only the adapter needs
>be different, not the Rockbox part.

Well, since I'm interfacing it directly what I could do was to make my code
as a kind of gateway from the bmw cd changer protocol to a "future standard"
archos inteligent remote protocol. The code would read messages from the bus
and place events in the extended button queue. The responses from the archos
would then need to be translated to IBUS messages again. I think it still
could be done. In fact I think it would be a good idea to have the ability
to place some piece of code that would handle all the serial communication
of the archos. Do you think this could be done?

If the rest of the rockbox firmware, namely the part that handles button
events, could also handle the extended requests of this inteligent remote
protocol we could then select which module we would use to interface with
the world outside. A module for ALPINE mbus, another for BMW IBUS, another
one for the simple remote control, etc...

I think I have read the spec you made and found that it had a lot of
messages in common with the BMW CD changer protocol. As I guess it would
happen with all CD changer protocols.

>My Alpine interfacing is not intelligent, because I abandoned the external
>microcontroller approach. The AJB has to do the interfacing, protocol and
>changer emulation in an own module, the benefit is that I don't need
>hardware. But despite this, it will also be useful to have a common
>API for remote commands, I'd be just bypassing the RS232 command parser

That's right, the rockbox code could provide that super remote control API
and all that our emulators/gateways would need to do was to handle
input/output and protocol translation... Perhaps it could even be in the
form of a loadable plugin...

>> PS. I will make the code available to all those interested. It is just
>> that
>> there are still some quite ugly piece of code in there and a bunch of
>> bugs.
>Yes, I'm interested.

Do you want it right now (it's full of ugly test code) ? If yes, please let
me know where to send it...

Fernando Birra
Received on 2004-04-01

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