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Subject: Re: archos as a cd changer
From: jobarjo (jobarjo78_at_yahoo.fr)
Date: 2004-04-01


Fernando Birra wrote:

>Hi Jörg,
>
>
>
>>"[IDC]Dragon" <idc-dragon_at_gmx.de> escreveu na mensagem
>>
>>
>news:25439.1080811588_at_www63.gmx.net...
>
>
>>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
>>
>>
>external
>
>
>>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
>transmit...
>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.
>
>
this is surely a ground noise problem. try to use a separate ground
signal which is not connected to the power amplification.
Use of coaxial or shielded cables might also help?

>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.
>
>
you should remove unnecessary connections, since they could bring noises.

>
>
>>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
>>
>>
>a
>
>
>>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
>>
>>
>to
>
>
>>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.
>
>
>
this spec cannot apply in your case because you have a direct connection
to the CDC.
however, yes we can share a common interface through the button queue
for one way.
and simply use memory directly for retrieving status?
This way we can work with interrupts, and we are all free to implement
any protocol...

>>My Alpine interfacing is not intelligent, because I abandoned the external
>>microcontroller approach. The AJB has to do the interfacing, protocol and
>>
>>
>CD
>
>
>>changer emulation in an own module, the benefit is that I don't need
>>
>>
>external
>
>
>>hardware. But despite this, it will also be useful to have a common
>>
>>
>internal
>
>
>>API for remote commands, I'd be just bypassing the RS232 command parser
>>
>>
>part.
>
>
>
>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...
>
>
>
beware that this API should work in an interrupt handler...
The problem of the plugin is that it has to be loaded...
definitly, it should be simpler to select the module at compile time, or
implement an autoload feature with a terminate and stay resident (TSR)
feature...

>>>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...
>
>
>
>>Jörg
>>
>>
>>

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