Method to Eliminate Data Bus Turnaround Penalty in a Parked Bus Utilizing a "Get Off The Bus" Signal
Original Publication Date: 2000-Mar-01
Included in the Prior Art Database: 2003-Jun-20
Method to Eliminate Data Bus Turnaround Penalty in a Parked Bus Utilizing a "Get Off The Bus" Signal Disclosed is a method for eliminating the data bus turnaround penalty when switching bus masters on a parked data bus by using a sideband "Get Off The Bus" signal. This invention allows one bus master to park on a data bus using the "bus hogging" method while not affecting data bus ownership turnaround time when other potential bus owners request the data bus. "Bus hogging" is defined as holding the data bus ownership after receiving a single data bus grant for multiple data transfers or even when merely waiting for data to transfer. This increases data throughput by eliminating request/grant sequences for subsequent data transfers from the same bus master. The downside is a turnaround latency due to the time it takes to unpark a "bus hog". This undesirable latency is eliminated by asserting the new sideband "Get Off The Bus" signal twice to the parked "bus hog", once when other potential bus owners request the data bus and again when a data bus grant is given for such a request. The "bus hog" is then obliged to release the data bus as soon as it has completed all committed data transfers after seeing this new "get off the bus" signal. The specific invention involves adding logic to a data bus arbiter between two or more devices requesting a common data bus. One of the devices has the ability to "park" itself on the data bus by holding a data bus busy signal active, thus hogging the data bus, after getting a data bus grant. A new sideband signal, "Get Off The Bus" is sent from the arbiter to the parked device for two cycles whenever another device requests the data bus and again when the arbiter grants the data bus for such a request. The parked device may finish any data transfers it has committed itself to doing and then must release the data bus after having seen this new signal go active.