Bus protocol and method for controlling a data processor
First Claim
1. A microprocessor implemented bus protocol method for controlling a bus transfer with a bus controller, the method comprising the steps of:
- granting bus ownership to a master circuit by asserting a first control signal from a bus controller wherein the granting is conditioned only on the first control signal;
transferring data between the master circuit and a device external to the master circuit in response to the assertion of a second control signal which indicates that the bus transfer is to initiated;
sending a third control signal from the bus controller to the master circuit wherein the third control signal indicates to the master circuit whether the master circuit bus ownership should be relinquished at the termination of a current bus cycle when the first control signal is deasserted or should be terminated at the discretion of the master circuit when the first control signal is deasserted;
deasserting the first control signal to indicate to the master circuit that the bus ownership should be relinquished;
relinquishing the bus ownership at either the termination of the current bus cycle or at the discretion of the master circuit as determined by the third control signal; and
communicating external to the master circuit that the master circuit has terminated its bus ownership by asserting a fourth control signal wherein the fourth control signal is asserted by the master circuit, the fourth control signal being asserted at a time which is determined by the state of the third control signal and the first control signal, the fourth control signal being tri-stated during bus ownership by the master circuit, being tri-stated during lack of bus ownership by the master circuit, and only being asserted when bus ownership is being transitioned between a granted state and an ungranted state with respect to the master circuit.
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Accused Products
Abstract
A bus protocol uses signals to designate a bus transfer termination (BTT*) and a bus grant relinquish (BGR*). The BTT* signal is an output which is asserted by a bus master which currently has ownership of a bus to indicate to other potential bus masters that a bus transfer is complete and that bus ownership may be transferred to another bus master. The BGR* signal is an input to a bus master. When BGR* is asserted, a bus arbiter/controller is informing the current bus master that the bus must be relinquished as soon as possible, after the deassertion of the Bus Grant signal, with no regard for locked sequences. If BGR* is deasserted, the bus arbiter is informing the current bus master that the bus can be relinquished at a time which is convenient for the current bus master. In general, BGR* is a bit which indicates the urgency of a pending bus ownership transfer.
26 Citations
25 Claims
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1. A microprocessor implemented bus protocol method for controlling a bus transfer with a bus controller, the method comprising the steps of:
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granting bus ownership to a master circuit by asserting a first control signal from a bus controller wherein the granting is conditioned only on the first control signal; transferring data between the master circuit and a device external to the master circuit in response to the assertion of a second control signal which indicates that the bus transfer is to initiated; sending a third control signal from the bus controller to the master circuit wherein the third control signal indicates to the master circuit whether the master circuit bus ownership should be relinquished at the termination of a current bus cycle when the first control signal is deasserted or should be terminated at the discretion of the master circuit when the first control signal is deasserted; deasserting the first control signal to indicate to the master circuit that the bus ownership should be relinquished; relinquishing the bus ownership at either the termination of the current bus cycle or at the discretion of the master circuit as determined by the third control signal; and communicating external to the master circuit that the master circuit has terminated its bus ownership by asserting a fourth control signal wherein the fourth control signal is asserted by the master circuit, the fourth control signal being asserted at a time which is determined by the state of the third control signal and the first control signal, the fourth control signal being tri-stated during bus ownership by the master circuit, being tri-stated during lack of bus ownership by the master circuit, and only being asserted when bus ownership is being transitioned between a granted state and an ungranted state with respect to the master circuit. - View Dependent Claims (2, 3, 4)
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5. A data processing system having a bus protocol for allowing a first circuit to interface to a second circuit through a bus, the data processing system comprising:
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circuitry for providing a first control signal as an output from the first circuit to indicate that ownership of the bus is requested; circuitry for receiving a second control signal as an input to the first circuit which is used to indicate whether the first circuit is granted ownership of the bus; and circuitry for providing a third control signal as an output from the first circuit wherein the third control signal is asserted only when the first circuit is ready to relinquish ownership of the bus, the third control signal being tri-stated during a first time period when the first circuit has control of the bus, being tri-stated during a second time period when the first circuit lacks control of the bus and being asserted to both a high voltage and a low voltage in a time sequential and mutually exclusive manner in two clock cycle time period when transitioning in time from the first time period to the second time period. - View Dependent Claims (6, 7, 8, 9, 10)
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11. A microprocessor implemented bus protocol for allowing a first circuit to interface to a second circuit through a bus, the bus protocol comprising:
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means for providing a first control signal as an output from the first circuit to indicate that ownership of the bus is requested; means for receiving a second control signal as an input to the first circuit which is used to indicate whether the first circuit is granted ownership of the bus; and means for receiving a third control signal as an input to the first circuit wherein the third control signal is set to a first logic state to indicate that the first circuit must relinquish bus ownership in response to deassertion of the first control signal at the end of a current bus cycle being performed by the first circuit when the deassertion of the first control signal occurs and wherein the third control signal is set to a second logic state to indicate that the first circuit is to relinquish bus ownership in response to deassertion of the first control signal at a convenient time determined by the first circuit when the deassertion of the first control signal occurs. - View Dependent Claims (12, 13, 14, 15, 16)
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17. A microprocessor implemented bus protocol for allowing a first circuit to interface to a second circuit through a bus, the bus protocol comprising:
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means for providing a first control signal as an output from the first circuit to indicate that ownership of the bus is requested; means for receiving a second control signal as an input to the first circuit which is used to indicate whether the first circuit is granted ownership of the bus; means for receiving a third control signal as an input to the first circuit wherein the third control signal is set to a first logic state to indicate that the first circuit must relinquish bus ownership at the end of a current bus cycle being performed by the first circuit and wherein the third control signal is set to a second logic state to indicate that the first circuit is to relinquish bus ownership at a convenient time determined by the first circuit; and means for providing a fourth control signal as an output from the first circuit wherein the fourth control signal is asserted only when the first circuit is ready to relinquish ownership of the bus, the fourth control signal being tri-stated during a first time period when the first circuit has control of the bus, being tri-stated during a second time period when the first circuit lacks control of the bus, and being asserted to both a high voltage and a low voltage in a time sequential and mutually exclusive manner in a two clock cycle time period when transitioning in time from the first time period to the second time period. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24)
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25. A microprocessor implemented bus protocol method for allowing a first circuit to interface to a second circuit through a bus, the bus protocol method comprising the steps of:
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providing a first control signal out from the first circuit to indicate that the first circuit is requesting ownership of the bus; providing a second control signal into the first circuit which is used to indicate whether the first circuit is granted ownership of the bus; and providing a third control signal into the first circuit wherein the third control signal is set to a first logic state to indicate that the first circuit must relinquish bus ownership at the end of a current bus cycle being performed by the first circuit and wherein the third control signal is set to a second logic state to indicate that the first circuit is to relinquish bus ownership at any time which is subsequent to deassertion of the second control signal, said time being a convenient time determined by the first circuit, the first control signal only performing bus granting functions where the first control signal is not used to communicate information identical to the third control signal.
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Specification