The address mapping utilities required for dma operations are not available. The FRS offers efficient, flexible support for periodic scheduling of IRIX TM processes, as required by many real-time simulation and data acquisition applications. The FRS is a kernel module that cyclically schedules processes at intervals defined by an interrupt. Instead, process scheduling is triggered by a periodic interrupt from a source selected at the time the FRS is initialized. The FRS provides general-purpose kernel support for periodic scheduling of IRIX processes Each incoming interrupt triggers a minor frame of the FRS .
Every minor frame is associated with a queue of processes to be run within that frame.
The list of processes in the queue is maintained in priority order, which specifies the order in which the processes will be run. In addition to a priority, each process is assigned an attribute which specifies its preemption behavior. For example, a process can either be required to complete execution within a minor frame, or be allowed to continue execution during the next minor frame. The selection of available attributes makes the FRS a general-purpose mechanism that can be tailored to meet a wide range of scheduling requirements. A user-defined number of minor frames comprise a major frame.