Method and apparatus for controlling a master abort in a computer system

A method of controlling a transaction in a computer system having a bridge coupled to a first bus and a second bus, the system including a first initiator device and a first target device coupled to the first bus and a second initiator device and a second target device coupled to the second bus, the first initiator device having a higher priority than the second initiator device, the method comprising the steps of:

• determining whether the first initiator device is allowed to access the first bus, when the second initiator device has been allowed to access the first target device;
• transmitting a target retry from the bridge to the first initiator device, when the second target device is specified as a target of a transaction of the first initiator device, in response to the determining step;
• and
• deasserting a bus access enable signal granted to the second initiator device, when the first initiator device is allowed to access the first bus.

An apparatus for controlling transactions in a system having a first bus, a second bus, a first agent coupled to the first bus, a second agent coupled to the second bus, a first target device coupled to the first bus, and a second target device coupled to the second bus, the first agent having a higher priority than the second agent, comprising:

• bus arbiter means, coupled to the first bus, for arbitrating bus accesses by transmitting bus access request signals and corresponding bus access enable signals to devices on the first bus;
• bridge means, coupled to the first bus and the second bus, for transmitting a bus access request signal from the second agent to the bus arbiter means on the first bus and for receiving, from the bus arbiter means, a bus access enable signal corresponding to the bus access request signal to allow the second agent to access the first bus;
• means, coupled to the first bus and the second bus, for determining whether the first agent transmits a transaction to the second target device before the second device completes a transaction in which the first target device has been accessed;
• means, responsive to the determining means, for transmitting a target retry to the first agent when it is determined that the first agent transmits a transaction to the second target device;
• means for determining whether a bus access enable signal corresponding to the second agent is deasserted;
• and
• means for terminating the second agent's access to the first target device, when the bus access enable signal is deasserted.

A method of controlling transactions between a first bus and a second bus via a bridge, comprising the steps of:

• arbitrating bus accesses by transmitting bus access request signals and corresponding bus access enable signals to devices on the first bus;
• first transmitting a bus access request signal from the second agent to the first bus;
• first determining that a first agent coupled to the first bus has a higher priority than a second agent coupled to the second bus;
• receiving a bus access enable signal corresponding to the bus access request signal to allow the second agent to access the first bus;
• second determining whether the first agent has initiated a transaction for execution by a second target device coupled to the second bus, before the second agent completes a transaction in which a first target device coupled to the first bus has been accessed;
• second transmitting a target retry to the first agent when the first agent has initiated a transaction for execution by the second target device;
• third determining whether a bus access enable signal corresponding to the second agent is deasserted;
• and
• terminating the second agent's access to the first target device, when the bus access enable signal is deasserted.