Unless you are manufacturing your own line of products, embedded development starts with a customer wanting to create or improve a new or existing product.
Then follows a lot of question and answer and,l usually, research to identify the possible range of solutions, from off-the-shelf to fully-custom, and consider their respective strengths and weaknesses.
If it seems to both parties that a custom solution is the best option, you may have work to do, if the business matters are agreeable to you both.
Then, in theory, begins the thinking and design of a possible solution, although in practice quite a few possibilities will usually have occurred to the designer during the discovery phase.
The next step is fleshing out the component parts of the overall solution, which may start as no more than a few quickly drawn ideas, like so -
These rough ideas are frequently tested by the designer, either as components, or as a part of a whole solution. Whilst the older method is to build test hardware, a lot of people opt for simulation nowadays.
In order to produce the prototype, the schematic designs must be entered into the design tool and parts created and added to the library if it does not contain the required part, or not one in the required physical package.
When the complete schematic is entered and verified for electrical consistency, the board layout can be performed. An important first step here is entering the manufacturing capabilities of the PCB company as a set of design rules that your board must conform to.
When the layout is complete, a set of files can be sent to the PCB manufacturer and a small batch of prototype boards ordered. It can typically take 5-10 days to receipt of the finished boards, although speedier options exist for higher prices.
This board is mostly Surface-Mount, apart from power devices all lined up to share a common heatsink and the much cheaper through-hole electrolytic capacitors. The hardest-to-solder ARM processor goes on first to give unimpeded access to it!
Once the prototype is fully debugged, actual assembly will be performed at the PCB manufacturers, but for the prototype it's a job for a good eye and a steady hand.
Once all parts are fitted, the board can be fitted into the prototype hardware and then the software programming and debugging can commence!
In this case, a JTAG port makes software development and testing much easier.
Larger size photo's can be viewed in this Flickr set.