I am developing an embedded real time system software (in C language). I have designed the s/w architecture - we know various objects required, interactions required between various objects and IPC communication between tasks. Based on this information, i need to decide on the operating system(RTOS), microprocessor and memory size requirements.

(Most likely i would be using Quadros, as it has been suggested by the client based on their prior experience in similar projects)

But i am confused about which one to begin with, since choice of one could impact the selection of other.

Could you also guide me on parameters to consider to estimate the memory requirements from the s/w design (lower limit and upper limit of memory requirement) ?

(Cost of the component(s) could be ignored for this evaluation)