> Most of the players have an Actions ATJ2085 CPU chip > http://www.actions.com.cn/en/product.aspx?id=10 and can indeed play OGG > files (though their website doesn't say this) I'd say that this CPU/microcontroller is the most limiting factor to get Rockbox on these players: Rockbox is only built for and running on 32 bit cpu cores, so this Z80 8/16? bit will require some work to get Rockbox for. We once had it buildable for a 16bit CPU (calmrisc for one of the older Archos gmini models), but that particular port was abandoned and most of the long/int cleanups of those days are likely gone by now.The data sheet says 8bit! There is a DSP that does the MP3 decoding and a DMA controller, so most likely the z80 does little besides reading the FAT filesystem and setting up the DMA to pipe data from Flash to the DSP.
It also handles keyboard and screen, loads the dac into the dsp, tells the radio what to do, and a few other trivial tasks.
