We are using EM8623 for the development of set-top-box and digital signage applications.
In order to develop for that platform, an SDK must be purchased directly from Sigma Designs.
However, the linux kernel is open source so companies need to release the source if they modified it in their products.
For example, you could download the GPL source released by Kiss Technology – http://www.kiss-technology.com/files/firmware/GPL.zip. This is only the GPL source for your reference, after that there are also sigma linux drivers (not released by sigma) and not GPL, and the MRUA package that needs to be purchased from Sigma Designs.
One the challenge of using EM862X platforms (EM8620L, EM8621L, EM8622L, EM8623L etc..) is that it has no MMU (Memory Management Unit) and that may make the software debugging very interesting.. You may experience spectacular crashes, kernel panic without any apparent reason. But most of the time this is due to a stack overflow of the main process or one the threads used. Having nommu also introduces some limitations such as the absence of fork, dynamic libraries and memory fragmentation. There is a lot of literature about those on the internet and I strongly recommend reading the links below if you develop applications for a nommu platform based on ucLinux.