Detecting the presence of a device on a computer system bus by measuring the response time of data signals on bus, and maximizing system performance based on that response time

摘要

A computer system determines the presence of a device attached to a system bus that responds to I/O or memory reads by driving the data lines of that bus to values normally present on an undriven bus. The data bus is first driven to a value other than its undriven value, such as to 00h. Then, circuitry measures the time it takes on an I/O or memory read for the data bus to return to its normally undriven value. If the response time is less than the time it takes for an undriven data bus to return to its undriven state, then an expansion board is driving the data bus to its normally undriven value. This indicates that the expansion board is responding to an I/O or memory read on the data bus, even though it is responding by driving that bus to its normally undriven value. Further, by determining the maximum response time of a device, system performance is then improved by tuning cycle time to correspond to that maximum response time.