High level message priority assignment by a plurality of message-sending nodes sharing a signal bus

• US 20060098682A1
• Filed: 12/22/2005
• Published: 05/11/2006
• Est. Priority Date: 02/06/2001
• Status: Active Grant

• Current Assignee: Ademco Inc. (Resideo Technologies, Inc.)
• Original Assignee: Honeywell International Inc.
• Inventors: Nichols, Steven C.
• Granted Patent: US 7,664,133 B2
• Time in Patent Office: Days
• US Class Current: 370/447
• CPC Class Codes: G06F 13/374 using a self-select method with individual priority code comparator
• CPC Class Codes: G06F 13/376 using a contention resolving method, e.g. collision detection, collision avoidance

Abstract

A system has a plurality of nodes communicating with each other on a serial data path using dominant and recessive signal levels. A dominant signal level sent on the data path by any of the nodes creates a dominant signal level on the data path irrespective of the number of recessive signal levels sent by other nodes. The dominant and recessive signal levels form a series of bits organized into messages by the nodes. Each sending node senses the signal level on the data path bit by bit, and if different from that sent by that sending node, halts further sending of signal levels by that sending node. A priority value generator in each node provides a priority signal encoding a value whose magnitude indicates a relative priority. A message priority module in each node receives the priority signal, and stores the priority value in predetermined leading bits of the message to be sent.

Claims

1. A node operable in a data processing arrangement including a plurality of the nodes that are capable of communicating with one another via a serial bus, the node comprising:

a send register for storing a message for transmission on the serial bus, wherein the message comprises at least a data ID including a content identifier inherently exhibiting a first bus arbitration priority;

a message priority module configured to store a second bus arbitration priority contiguous with the data ID of the message; and

a transmitter coupled to the message priority module to receive the message, and to serially transmit onto the serial bus the message as dominant and recessive signal levels in a bit format ordered from the second bus arbitration priority to the first bus arbitration priority.

2. The node as in claim 1, further comprising a monitor circuit coupled to the serial bus to monitor the dominant and recessive signal levels on the serial bus, and configured to disable further transmission of the message if a dominant signal level is present on the serial bus when a recessive signal level is being transmitted by the node onto the serial bus.

3. The node as in claim 2, wherein the monitor circuit comprises:

an input interface coupled to the serial bus and configured to convert the dominant or recessive signal level on the serial bus to a logic state; and

a data processor coupled to the input interface to receive the logic state and to disable further transmission of the message if the logic state represents a dominant signal level when a recessive signal level is being transmitted by the node onto the serial bus.

4. The node as in claim 2, wherein the monitor circuit is further configured to enable further transmission of the message if a dominant signal level is present on the serial bus when a dominant signal level is being transmitted by the node onto the serial bus.

5. The node as in claim 4, wherein the monitor circuit comprises:

an input interface coupled to the serial bus and configured to convert the dominant or recessive signal level on the serial bus to a logic state; and

a data processor coupled to the input interface to receive the logic state and to enable further transmission of the message if the logic state represents a dominant signal level when a dominant signal level is being transmitted by the node onto the serial bus.

6. The node as in claim 1, wherein the second bus arbitration priority represents a relative priority to access the serial bus by a relative placement of dominant bits corresponding to dominant signal levels.

7. The node as in claim 6, wherein the dominant bits placed in more signficant bits of the second bus arbitration priority represent higher relative priorities than the dominant bits placed in less signficant bits of the second bus arbitration priority.

8. The node as in claim 1, wherein the first bus arbitration priority represents a relative priority to access the serial bus by a relative placement of dominant bits corresponding to dominant signal levels.

9. The node as in claim 8, wherein the dominant bits placed in more signficant bits of the second bus arbitration priority represent higher relative priorities than the dominant bits placed in less signficant bits of the second bus arbitration priority.

10. The node as in claim 1, further comprising a priority value generator coupled to the message priority module to generate the second bus arbitration priority for use by the message priority module in storing the second bus arbitration priority contiguous to the data ID.

11. The node as in claim 1, wherein the message priority module is configured to store the second bus arbitration priority immediately preceding the data ID of the message.

12. The node as in claim 1, wherein a plurality of the messages are provided at the node, and wherein the send register comprises a plurality of storage locations to store the plurality of messages for transmission on the serial bus.

13. The node as in claim 12, wherein the plurality of messages are stored in the send register in a transmission order ranging from the messages associated with a highest of the second bus priorities to the messages associated with a lowest of the second bus priorities.

14. The node as in claim 13, wherein the transmitter is further configured to serially transmit the plurality of messages according to the transmission order onto the serial bus.

15. The node as in claim 1, wherein second bus arbitration priority comprises two priority bits.

16. The node as in claim 1, wherein the second bus arbitration priority comprises two priority bits representing priorities ranging from a lowest priority of binary 11 and a highest priority of binary 00.

17. A system for enabling a plurality of nodes to arbitrate for access to a serial bus by which the nodes communicate, comprising:

(a) a sending node comprising;

(i) a send register for storing a first message for transmission on the serial bus, wherein the first message comprises at least a data ID including a content identifier inherently exhibiting a first bus priority;

(ii) a message priority module configured to store a second bus priority contiguous with the data ID of the first message;

(iii) a transmitter coupled to the message priority module to receive the first message, and to serially transmit onto the serial bus the message as dominant and recessive signal levels in a bit format ordered from the second bus priority to the first bus priority; and

(b) a receiving node comprising a monitor circuit coupled to the serial bus to monitor the dominant and recessive signal levels on the serial bus, and configured to disable firther transmission of a second message being transmitted from the receiving node if a dominant signal level is present on the serial bus when a recessive signal level is being transmitted by the receiving node onto the serial bus.

18. A method for communicating via a serial bus at least one message from a source node to one or more recipient nodes, comprising:

assembling a message at the source node, wherein the message includes at least a data ID field for providing a content identifier inherently exhibiting a first bus priority, and a priority field for providing a variable priority, and wherein the priority field is assembled immediately preceding the data ID field in an order from leading bits to trailing bits;

transmitting the assembled message bit by bit from the source node onto the serial bus as dominant and recessive signal levels in a bit format ordered to transmit the priority field immediately prior to the data ID field in the order from leading bits to trailing bits;

monitoring the dominant and recessive signal levels on the serial bus;

disabling further transmission of the message from the source node if a dominant signal level associated with the variable priority of at least one of the recipient nodes is present on the serial bus when a recessive signal level associated with the variable priority of the source node is being transmitted onto the serial bus; and

if the variable priorities of the source node and the one or more recipient nodes differ, granting access to the serial bus to the source node or the recipient node having the highest variable priority.

19. The method of claim 18, wherein the variable priority of the source node and the at least one of the recipient nodes are equivalent, and further comprising disabling the further transmission of the message from the source node if a dominant signal level associated with the first bus priority of the at least one of the recipient nodes is present on the serial bus when a recessive signal level associated with the first bus priority of the source node is being transmitted onto the serial bus.

20. The method of claim 19, further comprising granting access to the serial bus to the source node or the recipient node having the highest first bus priority, if the variable priorities of the source node and the one or more recipient nodes do not differ.

21. The method of claim 18, further comprising arranging a plurality of the messages available for transmission from the source node onto the serial bus into a transmission order dependent on the variable priority.

22. The method of claim 21, wherein arranging a plurality of the messages comprises arranging the plurality of the messages into a transmission order from a highest variable priority to a lowest variable priority, and further comprising transmitting the plurality of messages according to the transmission order.