Where should I start on embedded learning?

lingfeng_li

I have been working on firmware for more than 10 years, mainly on communication, multimedia and DSP, and I use only systems developed by my company.But once I look outside, I found I am not familiar to most comecial RTOS system and it will be difficult for me to get a new job outside my company.
My question:
1. What HW and RTOS is most widely used in industry? I know there are ARM/MIPS/POWER PC/X86 in hardware, and uc-os, nucleus, linux in RTOS, I think these are majorly used in industry.
2. Which one is easier to learn? I know nothing is easy.  But give my experiece, I hope I can find one easier for me.  I have ARM programing experice, I am good at assembly (80x86, ARM) and c coding.  No experience on Java and C++.  I am familiar to communication protocal (GSM/CDMA, physical layer only),I am familiar to video codec (MPEG-4 and H.264) and I am good DSP programmer.
3. Which is better - reading linux source code? reading some typical books? 
Any suggestions from you experts?
Thanks in advance.