Currently I abondoned preparing firmware for my player. It causes too many problems, the firmware executes and enables upgrade mode but non of the devices are working properly.
look at this thread:
Google Tłumacz
the only thing which pushed me into own firmware is the support of opening external files. But in this thread SWIRL is saying that it can be done in RKP file, so if it works, there is no need to do this.
Also I ve been working on RKP platform and I am pretty close to MP3 support INSIDE RKP file, so I will be able to make my own mp3 player with AlbumArt support, spectrum analyzer and much more just by using RKP file.
The funny thing about original firmware is a huge loss of performence because of lazyness of programmers. The original firmware works in a way that graphics are displayed directly from flash data, so everytime something needs to be displayed, it looses a lot of time to read from flash.
What I noticed is that when the graphics are preloaded into SDRam the performence of displaying graphics raises up to 10x faster. Spectrum analyzer will work like a charm, and everything should work a lot of faster even during mp3 playback.