Gameboy Advance is what really got me into embedded stuff. Might be a good "stepping stone" between regular PC game development, and direct fiddling with microprocessors and sensors and such. After you get used to working with memory mapped hardware registers, managing RAM by hand, writing ARM assembly and putting it in RAM instead of ROM so it runs faster, etc. you'll know how it is for programs to interact with hardware directly.

And at least for me, starting to play with stuff like AVR microprocessors after that, it all makes perfect sense how you can connect things up to do whatever you want. Programs read/write to hardware registers, where each bit of the register corresponds to a pin on the physical chip to either read from some other component, or set the pin's value to control another component... value being either positive voltage or negative voltage, representing binary 1 or 0. Although some pins can read a variable voltage value as an 8 or 16 bit number using some special circuitry to convert it, and some have pulse-width-modulator circuitry to toggle on and off at high speed according to a register value, effectively creating variable output voltage. And then you have the fun interaction between programming and physical routing of processor pins to other hardware :)

ARM assembly would definitely be good to learn. It's pretty straightforward. Practically like writing in a high level language compared to 6502 :) AVR assembly would be good too, and is sort of half way between ARM and 6502 (lots of general purpose CPU registers, but few opcodes)

I am looking for some advice from any embedded software engineers and/or mainframe programmers out there. Where should someone looking to develop real time systems really begin? I am turning 20 in August, figured I would really try and buckle down on something and this is it. I haven't gone to university at all because I still need to get my GED so until then specialized schooling is not an option. Since leaving high school I managed to pick up Perl, C, Lua, x86 (to some extent) and 6502 assembly but I'm not exactly interested in programming for video games anymore despite finding some small successes there. I find engine development and optimization on microprocessors to be much more fulfilling despite the mundane aspects of such tasks. The real question is, is there anything else I sould be doing to try and accomplish this? Are there any excersises I should be trying or particular languages (like learning to write ARM asembly?) I should highlight? Any other tips would be greatly appreciated, thanks!

Ah this really depends on where you want to go with embedded software. Do you want to develop for an embedded device like a phone or are you looking to develop your own systems from the ground up. When I got involved in embedded as a hobby I wanted to go ground up.

Some people suggested Arduino and in all honesty it is a great platform but it is exactly that a bloated platform that will hinder your growth at some point. It is great for just getting started but you will want to move away from it quickly.

In the current perspective assembler is not really needed C can do just fine but I prefer the assembler for 8 bit chips because there are quite a few gotchas you that will bite you at some point with C. For instance real time systems including video and time keeping are not really something C does well in the embedded process. One such example was my alarm clock built with a 8 bit PIC micro controller. I started with C and all was good but the C actually caused some issues when dealing with timing. C is not a 1 to 1 instruction setup and the actual generated assembler was throwing of my clock by quite a bit and with all the optimization I could possibly do it just was not accurate enough so I converted the important code to assembler to solve the timing issues.

As for Assembler every chip has it's own Assembler suite and non of them are identical. PIC is different then AVR which is different then ARM. From a assembly perspective PIC is much easier to learn and the chips are quite a bit cheaper as well.

This is of course assuming you want the ground up approach that I took. In which case you need to learn some electronics theory for circuit design, as well as programming a particular micro controller.

My recommendation would be AVR or PIC 8 bit chips to start. My opinion stands strong that Arduino is a waste of time if you really want to learn it is just wrappers on top of wrappers and bloat. The only advantage is rapid prototyping. I disliked it so much I pulled the chip and erased it and through the board away and kept the chip for a different project. But to each his own it might be what you want so don't rule it out because I said it is bad.

Embedded is a deep hole to swim in if you have no clue the direction you want to go but there are tons of people that can help you out. My suggestion is to get an account over at www.eevblog.com watch some of Dave's videos on youtube. Ask every question you can even if it is stupid you will get tons of valuable information. Just don't ask about ASM vs C because it is about as heated at C++ vs <insert language here> gets on these forums. Actually it is even worse just pick one and go for it don't worry about what others say.