While there are many requirements of an embedded operating system - the one that attracts the most attention is real time performance. Others, which can not be left out are:
Even though figures like the Interrupt latency, Context switch time are important, there are other parameters that will determine if an Operating System will make a good canidate for your real time requirements. For example a RTOS supporting many devices or networking will have more advantages than a simple very good nano-kernel.
"A real-time system is one in which the correctness of the computations not only depends upon the logical correctness of the computation but also upon the time at which the result is produced. If the timing constraints of the system are not met, system failure is said to have occurred."
According to the Comp.realtime FAQ what makes an Operating System an real time operating system are the following:
So the following figures should be clearly given by the OS manufacturer:
To determine how real time, uclinux is, we will try to provide the requirements stated above with some standard, and custom tools: