| 摘要 |
<p>A computer system comprises a plurality of devices (10), a CPU (11) which includes scheduling means (12) for scheduling the servicing of the devices by the CPU. Each device produces a priority level signal indicating the urgency with which that device needs servicing. There are 3 device status registers (20) and associated round robin registers (21), one for each possible priority level. A priority signal from a device sets the corresponding bit in the corresponding device status register. A priority determining circuit (22) determines the highest active priority level. The associated round robin register then determines which device the CPU should service next, and its bit is advanced to the next device (if any) at that priority level, i.e. to the next device in the corresponding device status register. Thus devices are normally processed in round robin fashion, but the system operates at a plurality of priority levels; only devices at the highest active priority level are eligible for servicing, but no device is ever locked out indefinitely,</p> |
