Accessing my music via the USB port on car stereo

[rockrockrock]

I have a Sansa Zip+ device with a recent version of RockBox installed.  I took the device on a long car trip, and wanted to access my music via the USB port on the car stereo.  I was hoping the stereo would see the device like a USB stick and be able to play my music.  It could see the device, but not my music.

Instead, I was stuck in my car for close to 24 hours with nothing to listen to but a stupid Slot Radio ad that came with the device.

Is there a way to access stored music from a radio via a USB cable?

Thanks!

[saratoga]

Is there a way to access stored music from a radio via a USB cable?

This is really a question for the company that made your car stereo, since you're basically just using your clip as an oddly shaped USB stick. 

[soap]

Is your music on the player itself, a SD card, or some combination thereof?

[rockrockrock]

The music is mostly (entirely?) on the SD card.

I disagree with the notion that this is primarily a car stereo issue.  When the device is connected via USB cable, it turns on and activates in some sort of slave mode.  I believe it is the music player and not the car stereo that selects what data is available in that mode.  My question is can I override the default Sansa behavior with RockBox.

[evilnick]

Have you tried booting your player to Rockbox and then plugging it into your car stereo?

It sounds as if you're plugging it in when the player is off, which will (?) boot the Original Firmware.

[saratoga]

When the device is connected via USB cable, it turns on and activates in some sort of slave mode.

That would be USB mode.

I believe it is the music player and not the car stereo that selects what data is available in that mode.

Its USB mode.  All the data is available.  Its up to your car stereo to figure out what to do with it though.

[Crafty]

The computer sees the SD as another storage device.  I dout a car stereo is going to read it.

Your car stereo does access the root-folder and\or 1 folder.  Maybe your car stereo stops searching for music files when it sees 1 or more empty sub folder.  It was programed this way to speed up access on cd's and memory stick with mixed music and data.
 
I would try putting a mp3 file in the root and all the sub-folder in the path.

[Crafty]

Found it.

to access the SD card:
setting->general setting->system->USB hide internal disk

[soap]

The music is mostly (entirely?) on the SD card.

I disagree with the notion that this is primarily a car stereo issue.  When the device is connected via USB cable, it turns on and activates in some sort of slave mode.  I believe it is the music player and not the car stereo that selects what data is available in that mode.  My question is can I override the default Sansa behavior with RockBox.

Let's be clear.  This appears to be a problem with your head unit.  I'm sure your head unit is functioning as it was intended, but the apparent inability to handle a USB device which presents multiple endpoints (which are not that uncommon) is the most likely cause.  Crafty has most likely posted the solution to your problem.  Don't let Rockbox show the internal drive and the SD card at the same time and the head unit will most likely play nice.