Bus arbitration

Details Bus arbitration Bus arbitration

1999-07-29

2003-11-25

Lefkowitz, Sumati (Department: 2181)

Electrical computers and digital data processing systems: input/

Intrasystem connection

Bus access regulation

C710S116000, C710S117000, C710S123000, C710S124000, C710S244000

Reexamination Certificate

active

06654833

ABSTRACT:

BACKGROUND
The invention relates to bus arbitration, such as arbitration on a local bus, for example.
Referring to
FIG. 1
, a typical computer system
8
may include a local bus
16
that may be owned for a particular bus operation by one of several bus agents. Because only one bus agent may own the local bus
16
at any particular time, the computer system
8
may use an arbitration scheme to determine which bus agent is granted ownership of the local bus
16
for the scenario in which multiple bus agents concurrently request ownership of the local bus
16
. In this manner, the arbitration scheme may classify a particular bus agent as being either a priority bus agent
14
(a system controller, for example) or a symmetrical bus agent (processors
12
a
,
12
b
,
12
c
and
12
d
, as examples).
The symmetrical bus agents have the same priority level, and if multiple bus agents request ownership of the local bus
16
for the next bus operation, then the arbitration scheme awards ownership of the local bus
16
to the bus agent that has least recently used the local bus
16
. To accomplish the above-described arbitration scheme, the local bus
16
may include bus request lines
17
that communicate bus request signals (called BREQ
0
#, BREQ
1
#, BREQ
2
# and BREQ
3
#, as examples), each of which may be driven by a different one of the processors
12
to request ownership of the local bus
16
.
The priority bus agent asserts a signal (called BPRI#) to request ownership of the local bus
16
. As its name implies, the priority agent
14
has a higher priority level than the symmetrical agents. Thus, if a symmetrical agent and the priority agent
14
concurrently request ownership of the local bus
16
, the arbitration scheme ensures that the priority agent
14
is granted ownership of the local bus
16
.
A difficulty with the above-described arrangement is that the priority agent
14
may become effectively parked on the local bus
16
and consume a substantial amount of the available bandwidth of the local bus
16
. As a result, the symmetrical agents may be deprived from adequate use of the local bus
16
.
Thus, there is a continuing need for an arrangement that addresses one or more of the above-stated problems.
SUMMARY
In one embodiment of the invention, a method for use with a computer system includes permitting a first bus agent to access a bus during predetermined windows of time and preventing a second bus agent from accessing the bus outside of the windows. The first bus agent has a higher priority than the second bus agent. Use of the bus by the second bus agent is monitored during the windows, and the duration of the windows are selectively regulated based on the use.
In another embodiment, a method for use with computer system includes permitting a first bus agent to access a bus during predetermined windows of time and preventing a second bus agent from accessing the bus outside of the windows. The first bus agent has a lower priority than the second bus agent. The second bus agent is prevented from accessing the bus during the windows, and use of the bus by the first bus agent is monitored during the windows. The durations of the windows are selectively regulated based on the use.
In yet another embodiment, a computer system includes a local bus, a processor that is coupled to the local bus, a system controller that is coupled to the local bus, and a circuit. The system controller has a higher priority than the processor for bus arbitration, and the circuit is adapted to permit the system controller to access the bus during windows of time and prevent the system controller from accessing the bus outside of the windows to permit the processor to access the bus, monitor use of the bus by the system controller during the windows, and selectively regulate the durations of the windows based on the use.


REFERENCES:
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patent: 5241632 (1993-08-01), O'Connell et al.
patent: 5499345 (1996-03-01), Watanabe
patent: 5560016 (1996-09-01), Fiebrich et al.
patent: 5581782 (1996-12-01), Sarangdhar et al.
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patent: 5822549 (1998-10-01), LaBerge
patent: 5845097 (1998-12-01), Kang et al.
patent: 5905878 (1999-05-01), LaBerge
patent: 5948094 (1999-09-01), Solomon et al.
patent: 6058450 (2000-05-01), LaBerge
patent: 6145040 (2000-11-01), LaBerge et al.

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