Ubuntu :: Access To Firmware Rockchip MP4 USB?

I have a 16GB MP4 player bought in China. It's based on the Rockchip RK27 chipset. I would like to access to the firmware through Linux, but I cannot access it. When I connect the MP4 player to my laptop it's correctly mounted, but it seems as it has two partitions but only one is mounted and accessible. The MP4 can be seen mounted as /dev/sdb

Code:
~$ mount
/dev/sda2 on / type ext4 (rw,errors=remount-ro)
proc on /proc type proc (rw,noexec,nosuid,nodev)
none on /sys type sysfs (rw,noexec,nosuid,nodev)
none on /sys/fs/fuse/connections type fusectl (rw)

[Code]...

I say that it is supposed to have two partitions, because when it's connected under Windows it takes two drive letters (one for the multimedia stuff and the other one it is not accessible either)

And in Linux in the File Explorer I can see what I assume are the two partitions (Rockchip USBDISK SD and Rockchip USBDISK User). But only the one labelled as User is mounted.