Given how big I'm into music (particularly game, anime, and movie soundtracks), it'll probably come as a complete shock to most people to know that I've never had a portable CD or MP3 player (other than the CD player in my car). Probably the biggest reason for this is that I'm cheap - I save most of the money I make, and spend very little of it, even on things you'd expect me to buy (like a computer that's less than 6 years old). Well, yesterday I just bought a digital audio player: the SanDisk Sansa c250 2 gig, on sale at a price I couldn't refuse (cheaper than Amazon).
So, I spent some time playing with it yesterday, in preparation of today, when I drive my grandma to a doctor's appointment and various errands (she's had severe eye problems for the last couple months). Not a bad little sucker; though just as you might guess from the price, it didn't take long to run into problems. Naturally, as I'm too impatient to call tech support, and too inquisitive to give up on a technical challenge, this meant I had to debug the thing.
After loading almost 2 gigs of music onto it and disconnecting from the computer, it proceeded to promptly lock up on database refresh (after you modify the contents of the flash memory it scans all the files and indexes them). Wonderful. I could turn it off and on, but every time it turned on it immediately performed a database refresh, and promptly locked up. Worse, it would no longer connect to the computer, as the database refresh preempted other things, like USB port communication, meaning I couldn't delete anything that might be causing it to freeze (specifically, if you plugged it into the USB port while it was performing the database refresh, Windows would say "unrecognized USB device" after a couple seconds).
A substantial amount of experimentation revealed that it was possible to override this. Specifically, you had to have the computer send a USB signal to the device BEFORE it starts its database refresh. As the database refresh is the first thing it does when you turn it on, and plugging the USB cable in automatically turns the device on, this takes rather precise timing, and more or less requires pressing the button required to make it connect in mass storage mode*, insert the USB cable, and press "Scan for hardware changes" in Device Manager at essentially the same time (I'd say about 1/3 of a second). This will cause the USB signal from the computer to preempt the scheduled database refresh, and put it into USB storage mode.
Now that I was able to access the contents again, I spent some time fumbling around with trial and error, trying to figure out what was causing it to break; as it was 1 AM by this point, my brain wasn't in peak working condition, and this took some time. Searches on Google revealed that quite a few people had this problem and there are quite a few hypotheses as to what causes it and how to fix it, but no definitive explanation or solution (nor has Sandisk addressed this problem, despite people asking for help on their forums). As well, many of the "solutions" involved wiping the memory of the thing, and sometimes bricking it.
Through trial and error, I managed to burn through a number of hypotheses (which were either incorrect or simply not applicable to me). It appeared to be false that spaces in directory and file names caused lockups (or that bug only occurred in older versions of the firmware). I also did not observe any instances of odd characters in song titles or artists that caused this problem; to my surprise, the device even correctly handled and displayed the Japanese characters in some song and artist names (when I had first opened the package, I tried copying a single album onto it, which worked without incident; this album happened to have Japanese ID3 info). Lack of free space did not appear to cause it (I tried taking it down to 2 megs free space with good files, and it still worked fine). ID3v1 tags seemed to work fine. Even this one funky MP3 at "0 kbps" (what Explorer reports for it; I haven't looked at it with a hex editor to figure out why this is) did not cause the problem.
What ultimately ended up being the problem, at least in my instance, was that one of my game soundtrack MP3s was mislabeled as 'hard rock'. The significance of this, according to one person, is that it has a space in the genre name. Changing this to the proper genre corrected the freeze. I can't say for certain that the space in the genre is what causes the bug, but it's true that when none of my songs have a space, the player works fine, and it froze in that one case.
*The Sansa has two USB connection modes: MTP and MSC. MTP mode interfaces with media players such as Windows Media Player. This mode allows you to store media library files on the player, and make use of various features like tagging and playlists. MSC mode causes the player to act like a vanilla memory stick, allowing you to directly access the flash file system. I'd imagine it's only necessary to refresh the database in MSC mode; that's the only mode I've ever used.
Judging from Google, there are two different methods of switching between modes, which depend on what firmware you have. One method is that a USB mode option appears in the settings menu on the device. The other method (what mine has) is that the player is always in MTP mode, but connects in MSC mode if you hold the rewind button when you plug it into the USB port.
Found another bug while playing around with putting DRMed WMAs on the critter (my dad also got one, and he has a bunch of DRMed WMAs to put on it, unlike my MP3s). It's only possible to load DRMed files onto the device in MTP mode, so I had to learn how to use that. It appears that my assumption was correct, that database refreshes are only necessary after adding files in MSC mode; after files are added in MTP mode, they appear in the player immediately after the player is disconnected from the computer.
While the player automatically turns on and goes into USB storage mode when you plug the USB cable in, it's possible to turn off the player by holding the power button (the same way you turn it off when it's not connected to the computer) while in USB storage mode. This is not a good idea. If you add some files to the device and then turn it off before unplugging it, it will lose track of those files, and they will not show up in the list of songs on the player (though they will still show up in the file list when it's connected to the computer in MTP mode). Adding additional files later will not cause this problem to be corrected; it is necessary to delete the files from the player and then transfer them from computer again