Method and apparatus of allocating minimum and maximum bandwidths on a bus-based communication system with redundant communication circuits
Access to a bus is granted to one of a number of requesting communication circuits that each submitted a bus control request during a request period of an arbitration period in response to grant information which can be stored in a primary and a backup priority table. If a requesting communication circuit has an identity and priority that match the identity and priority of a communication circuit stored in a row of the primary or backup priority table that corresponds with the arbitration period, and the identities stored in the tables match only one requesting communication circuit, access to the bus is granted to the requesting communication circuit.
1. A method of granting access to a bus to one of a plurality of requesting communication circuits that each submitted a bus control request during a request period of an arbitration period, the method comprising:
determining a first and a second stored identity associated with the arbitration period, the first stored identity identifies a first communication circuit, the second stored identity identifies a second communication circuit; and
determining whether any requesting communication circuit has an identity that matches the first or the second stored identity.
2. The method of claim 1 , further comprising:
identifying a matching communication circuit when a requesting communication circuit has an identity that matches the first or the second stored identity,
reading a stored priority associated with the matching communication circuit, the stored priority indicating a priority level of a data cell of the matching communication circuit; and
determining whether a priority of the matching communication circuit matches the stored priority.
3. The method of claim 2 , further comprising when the priority of the matching communication circuit matches the stored priority, determining if the first and second stored identities both match the identity of the matching communication circuit.
4. The method of claim 3 wherein when the identity of the matching communication circuit matches only the first or the second stored identity, outputting a grant to the matching communication circuit.
5. The method of claim 4
wherein the bus has a plurality of first control lines and a plurality of second control lines; and
further comprising when the first stored identity and the second stored identity both match the identity of the matching communication circuit, determining whether a bus control request with an identity that matched the first stored identity and a bus control request with an identity that matched the second stored identity came in on a same control line.
6. The method of claim 5 , and further comprising when the bus control requests came in on the same line, outputting a grant to the requesting communication circuit that has a lowest stored identity.
7. The method of claim 5 , further comprising when the bus control requests did not come in on the same control line, outputting a grant to the requesting communication circuit that sent a request in on the first control lines.
8. The method of claim 2 , further comprising when a requesting communication circuit does not have an identity that matches the first or the second stored identity, determining a selected communication circuit from the plurality of requesting communication circuits.
9. The method of claim 8 wherein the selected communication circuit is determined with a round robin.
10. The method of claim 2 wherein the priority of the requesting communication circuit is the priority of a data cell to be transmitted onto the bus by the requesting communication circuit.
11. A communications circuit comprising:
a transmit circuit to transmit information onto a cell bus;
a receive circuit to receive information from the cell bus;
a memory to store grant information regarding a plurality of arbitration periods, the grant information for each arbitration period including a first stored identity that identifies a first communication circuit, and a second stored identity that identifies a second communication circuit; and
a logic circuit connected to the transmit circuit, the receive circuit, and the memory to determine whether any communication circuits requested control of a bus during an arbitration period, the logic circuit to determine a first and a second stored identity associated with the arbitration period, and whether any requesting communication circuit has an identity that matches the first or the second stored identity.
12. The communications circuit of claim 11 wherein when a requesting communication circuit has an identity that matches the first or the second stored identity, the logic circuit identifies the requesting communication circuit as a matching communication circuit, reads a stored priority associated with the matching communication circuit, and determines whether a priority of the matching communication circuit matches the stored priority, the stored priority indicating a priority level of a data cell of the communication circuit.
13. The communications circuit of claim 12 wherein when the priority of the matching communication circuit matches the stored priority, the logic circuit determines if the first and second stored identities both match the identity of the matching communication circuit.
14. The communications circuit of claim 13 wherein when the identity of the matching communication circuit matches only the first or the second stored identity, the logic circuit outputs a grant to the matching communication circuit.
15. The communications circuit of claim 14
wherein the bus has a plurality of first control lines and a plurality of second control lines; and
further comprising the step of when the first stored identity and the second stored identity both match the identity of the matching communication circuit, the logic circuit determines whether a bus control request with an identity that matched the first stored identity and a bus control request with an identity that matched the second stored identity came in on a same control line.
16. The communications circuit of claim 15 wherein when the bus control requests came in on the same line, the logic circuit outputs a grant to the requesting communication circuit that has a lowest stored identity.
17. The communications circuit of claim 15 wherein when the bus control requests did not come in on the same control line, the logic circuit outputs a grant to the requesting communication circuit that sent a request in on the first control lines.
18. The communications circuit of claim 12 wherein when a requesting communication circuit does not have an identity that matches the first or the second stored identity, the logic circuit determines a selected communication circuit from the plurality of requesting communication circuits.