Bus master arbitration circuitry having improved prioritization

A computer system, comprising:

• a bus for connection to a plurality of bus masters and bus slaves, each bus master requesting control of the bus by use of a bus request signal and receiving control by use of a grant signal, wherein bus masters may request a lock on a bus slave by using a lock signal, and wherein operation cycles of the bus masters can be directed to be retried by the bus slaves;
• at least one bus master connected to said bus;
• at least one bus slave connected to said bus, wherein one of said bus slaves provides an indication when a retried cycle can proceed;
• means connected to said bus for receiving the bus request signals;
• means connected to said bus for determining when an operation cycle is to be retried and if said operation cycle to be retried was directed to said bus slave which provides the retried cycle can proceed indication;
• means for determining the bus request priority of said bus masters with respect to each other;
• means connected to said bus and coupled to said bus request receiving means and said bus request priority determining means for granting control of said bus to the highest priority requesting bus master and providing the proper bus grant signal;
• and
• means coupled to said operation cycle retry means and said control granting means for masking the bus request of the retried bus master until said bus slave indicates that the retried cycle can proceed if the bus slave directing a retry to the bus master is said bus slave which provides said indication, unless the retried bus master has locked the bus slave and then the bus request is not masked.

A method for bus arbitration of a computer system, the computer system having a bus for connection to a plurality of bus masters and bus slaves, each bus master requesting control of the bus by use of a bus request signal and receiving control by use of a grant signal, wherein bus masters may request a lock on a bus slave by using a lock signal, wherein operation cycles of the bus masters can be directed to be retried by the bus slaves and wherein one of the slaves provides an indication when a retried cycle can proceed, the bus arbitration method comprising the steps of:

• receiving the bus request signals from the bus masters;
• determining when an operation cycle is to be retried and if said operation cycle to be retried was directed to the bus slave which provides the retried cycle can proceed indication;
• determining the bus request priority of the bus masters with respect to each other;
• granting control of the bus to the highest priority requesting bus master and providing the proper bus grant signal;
• and
• masking the bus request of the retried bus master until the bus slave indicates that the retried cycle can proceed if the bus slave directing a retry to the bus master is the bus slave which provides the indication, unless the retried bus master has locked the bus slave and then the bus request is not masked.