Canonical Service - A coding style template used for a real-time service provided by an RTOS task or thread. This style may vary, but at a minimum includes a main loop which executes as long as the service is “in service” and has a code section which either polls for input or synchronously or asynchronously waits for a service request.
Ceiling - The ceiling is a mathematical operation that can be performed on a real number (floating point) - the ceiling(n) is the closest integer whole number greater than or equal to n - e.g. ceiling(1.1) = 2. (note that floor(1.0) = ceiling(1.0) assuming that the significance is 1, which is the the typical definition of floor and ceiling unless otherwise noted).
CFD - Control Flow Diagram, a diagram used in Structured Analysis/Design which indicates where control signals in the system originate, where they terminate and how they change the flow of data and/or the processing of data in a DFD. (Note that a CFD is typically a subset of a DFD which shows both data flow and control flow).