My friend gave me this cheap little chinese MP3 player. I'm curious about exploring it learning more about the hardware, and potentially seeing if I could expand it's functionality in some way or run my own code on it to make it into something simple like a digital picture frame. Anything really I'm just curious about what it could potentially do but I don't know much about how feasible that would potentially be.
It doesn't have wifi or anything just a USB port, Bluetooth (audio), and an SD card slot. When I plug it in to my computer it shows up as a USB Mass Storage Gadget, which I understand is just an interface for transferring files to it. I asked the manufacturer about the processor inside and all he told me was "ATJ". My main machine is a mac with an Ubuntu dual boot.
I'd just like to get an idea of what might be feasible with this device and what might not be, as well as any tools or first steps for finding out more about the hardware or potentially being able to communicate with the device over USB or through the SD card. I don't care if I brick. I'm just curious about like, if an it was someone's job to figure out anything they could about this device, or make it run "Hello World" or something, what steps they might take to or what tools they might use to try to accomplish that. I also might be able to ask the company for more simple details but I'm not sure how much they would provide me.