At this point I'm 99% sure that disabling DMA is the "solution". I've run into no issues since disabling it and using the heck out of my iPod. Battery life doesn't appear to be
noticeably worse. Whatever decrease in battery life there may be (I might measure it one of these days) is arguably worth it to assure data integrity. As a nice (maybe not so surprising) side effect, it appears that Rockbox's USB mass storage functionality, which I'd avoided before in favor of the OF, also seems to finally have become reliable – although it may be too early to tell at this point.
I'm not sure why there would be issues with DMA (only?) on this device specifically – maybe there is someone reading this who is able to shed some light on that. But as I wrote in the other thread, my suggestion to any Rockbox developers reading this, would be to disable DMA on all iPod 4Gs for the time being. I.e.
removing line 234 from the file firmware/export/config/ipod4g.h The current implementation does not, in my experience, work reliably even on stock hardware. My bet would be that the only reason we haven't heard from more people about this is that there are
a) few people still using the target
b) even fewer using it extensively (like me and
the OP from the other thread)
c) they may be ascribing corruption issues to different causes or
d) can't be bothered to leave feedback about it.
Maybe I'm wrong, in which case, I'd be very interested in hearing from anyone who is using an unpatched version of Rockbox >= 3.13 on an iPod 4G target, who has not run into any issues after regularly using the device for many hours at a time (including database functionality)
Even better of course, would be making DMA work reliably on this model, but I'm not sure that is a realistic outcome in the short term (or possibly even long term).