Bus Master Mode of PCI-Bus. Part V

Use the parameter “PCI Latency Timer” (PCI Clocks) to specify the time during which the other devices control the bus operation. This parameter allows specifying (in cycles of PCI-bus) for how long some PCI-device that supports bus master-mode may retain control over the bus if it is requested by another device. After the time has expired, a bus conflict resolver forcibly takes a bus from the current bus host and sends it to another device. This parameter may have values from 16 cycles (16 CLK) to 128 cycles (128 CLK) with a step folded to 8 (16, 24, 32, …) and also the value “Auto Configured” that allows a system automatically setting the required control time. It is clear that the lower the set value is, the quicker another PCI-device would get the required access to a bus. But the time for controlling a bus depends on individual features of used devices and is determined by selecting an optimal value.