Kỹ thuật này có thể được sử dụng, tuy nhiên, kết hợp với các thông tin bổ sung từ kinh nghiệm thực tế và báo cáo của bên thứ ba. Hãy xem xét các tiêu chí lựa chọn mười ba, m1 · · · M13, mỗi có một phạm vi mi ∈ [0, 1] nơi mà sự thống nhất đại diện cho sự hài lòng cao nhất có thể về tiêu chuẩn và không đại diện cho nonsatisfaction hoàn thành. | MEMORY MANAGEMENT 135 technique can be used however in conjunction with supplemental information from actual experience and third-party reports. Consider thirteen selection criteria m1 m13 each having a range mị G 0 1 where unity represents the highest possible satisfaction of the criterion and zero represents complete nonsatisfaction. 1. The minimum interrupt latency m1 measures the time between the occurrences of hardware interrupt and when the interrupt s service routine begins executing. A low value represents relatively high interrupt latency while a high value represents a low latency. This criterion is important because if the minimum latency is greater than that required by the embedded system a different operating system must be selected. 2. This criterion m2 defines the most processes the operating system can simultaneously support. Even though the operating system can support a large number of tasks this metric may be further limited by available memory. This criterion is important for systems that need numerous simultaneous processes. A relatively high number of tasks supported would result in m2 1 while few task supported would suggest a lower value for m2. 3. Criterion m3 specifies the system memory required to support the operating system. It does not include the amount of additional memory required to run the system s application software. Criterion m3 1 suggests amin-imal memory requirement while m3 0 would represent a larger memory requirement. 4. The scheduling mechanism criterion m4 enumerates whether preemptive round-robin or some other task-scheduling mechanism is used by the operating system. If many mechanisms were supported then a high value would be assigned to m4. 5. Criterion m5 refers to the available methods the operating system has to allow processes to communicate with each other. Among possible choices are mutual exclusion mutexes binary and counting semaphores POSIX pipes message queues shared memory FIFO buffers control .
