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Subject: introducing the car CD changer project (your opinion, please)
From: idc-dragon_at_gmx.de
Date: 2003-03-19


Hello Rockbox world,

we are 3 guys seriously working on a car CD changer emulation since a while.
It started with my reverse engineering of the Alpine M-Bus protocol, now I
have an Atmel controller translating that to RS232 and can emulate a changer
with a PC. Changer emulation on the Atmel is subject of current work.

Diava made a new "real" serial driver for rockbox, capable of half duplex
bidirectional I/O at the remote control pin. As a spinoff he got his box
infrared remote controlled. Other usage is feasible, connect two boxes and play a
multiplayer game, etc. But it's too slow for reasonable data exchange.

The (unmodified) Archos will plug to a little controller box per headunit
brand, translating the manufacturer protocol to a generic format towards the
Archos. Please don't ask us for supporting especially yours, we're working on
my old Alpine protocol and VW/Audi. For anything else you're on your own, but
of course you'll know the rockbox end.

We can say the technical issues are cleared, are now facing the MMI
implementation. That's where we'd like your opinion. The radio should behave as
normal as possible, meaning we implement the controls of the radio (track and CD
select, search, shuffle, intro scan, etc.). We cannot display titles (only
track numbers), since our Alpine and VW gear does not support it. Some others
can, so we won't rule it out completely. We also prepare for an external
display connected to the adapter. Severe limitations are the (mostly) 6 CD buttons
and 99 tracks per CD. We have to somehow map that to the gigabytes on the
harddisk.

There is a nice concept from phatnoise, but it implies a certain directory
organization, something people can get religious about. So we don't like to go
that way.
http://www.phatnoise.com/owners/SSA_Glove_Box_Guide.pdf

We see 3 different ways, other may appear:
1. Full tree walk
We somehow abuse the 6 CD select buttons to walk the tree, like maybe 3
up/down pairs to walk the lowest directory level and the next 2 higher. Result
would depend on your tree organization, e.g. album, artist, genre. Perhaps a
bit confusing to do this "blindly".

2. Virtual CD magazines
You have to compile playlists which represent a magazine (with your PC or
maybe Rockbox). A magazine can be activated with Rockbox and then the normal
radio usage applies. Using radio controls, you cannot escape from that
magazine. Multiple magazines are possible, but you have to change them at the Archos.

3. Dynamic virtual magazine
You can compose the emulated magazine from the Archos directory browser,
like standing in front of your CD shelf and putting the disks in. I envision
pressing F1 on a directory or playlist, select CD emulator, then select which
slot to put it in.

Some more thoughts about car usage:
- We'd like a seperate (fixed?) volume/sound set for car mode, so it's
independent of how you used it last time when walking around.
- Probably you listen to different music in the car than elsewhere. So you
may not need or want to search your full collection.
- The adapter should allow a real changer to be connected behind and go to
passive mode if no Archos is connected, so you can use your regular changer
then.
- Archos powerup is problematic. The adapter cannot switch it on, so you
need to do that manually.
- In case you can mount the Archos in a nicely visible position (e.g. with a
mobile phone bracket) it would be useful to have a simplified display on it
with a large font.

Other opinions and rockbox implementation hints are welcome. We'd like to
implant this with minimum interference to rockbox, but on the other hand it's
like an alternative MMI. I'd like to have normal use of the rockbox MMI even
in changer emulation mode (so that e.g. passengers can operate it), but I'm
not shure if we can allow that. And certainly we'd like to be part of the
normal rockbox development, not an exotic spinoff.

So long,
Joerg

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