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

• US 7,664,133 B2
• Filed: 12/22/2005
• Issued: 02/16/2010
• Est. Priority Date: 02/06/2001
• Status: Expired due to Fees

• Current Assignee: Ademco Inc. (Resideo Technologies, Inc.)
• Original Assignee: Honeywell International Inc.
• Inventors: Nichols, Steven C.
• Primary Examiner(s): Juntima; Nittaya
• Application Number:
  US11/316,122
• Publication Number:
  US 20060098682A1
• Time in Patent Office: 1,517 Days
• Field of Search: 370/445, 370/447, 370/461, 370/462
• 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, wherein the content identifier represents a pre-assigned priority of the message content;

a message priority module configured to store a variable bus arbitration priority contiguous with the data ID of the message, wherein the variable bus arbitration priority is computationally adjustable by the node to change the pre-assigned priority of the message content; 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 variable bus arbitration priority to the first bus arbitration priority, wherein the data processing arrangement grants serial bus access to a selected one of the plurality of nodes having the highest first bus arbitration priority, if the variable bus arbitration priorities of the plurality of nodes do not differ.

2. The node as in claim 1, further comprising a monitor circuit coupled to the serial bus to monitor 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 variable 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 significant bits of the variable bus arbitration priority represent higher relative priorities than the dominant bits placed in less significant bits of the variable 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 significant bits of the first bus arbitration priority represent higher relative priorities than the dominant bits placed in less significant bits of the first 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 variable bus arbitration priority for use by the message priority module in storing the variable bus arbitration priority contiguous to the data ID.

11. The node as in claim 10, wherein the priority value generator is configured to dynamically modify the variable bus arbitration priority based on a condition sensed via the data processing arrangement.

12. The node as in claim 11, wherein the condition sensed via the data processing arrangement comprises determining the node has lost arbitration a predetermined number of times.

13. The node as in claim 11, wherein the condition sensed via the data processing arrangement comprises determining that a control range of the data processing arrangement has been exceeded.

14. The node as in claim 1, wherein variable bus arbitration priority comprises two priority bits.

15. The node as in claim 14, wherein the variable bus arbitration priority comprises two priority bits representing priorities ranging from a lowest priority of binary 00 and a highest priority of binary 11.

16. The node as in claim 1, wherein a highest priority value of the variable bus arbitration priority is reserved for a safety-critical situation.

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, wherein the content identifier represents a pre-assigned priority of the message content;

(ii) a message priority module configured to store a variable bus priority contiguous with the data ID of the first message, wherein the variable bus arbitration priority is computationally adjustable by the sending node to change the pre-assigned priority of the message content;

(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 variable 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 further 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, wherein, if the variable priorities of the respective first and second messages differ, the sending node and the receiving node grant serial bus access to the sending node or the receiving node having the highest variable bus priority in the respective first and second messages, and if the variable priorities of the respective first and second messages do not differ, the sending node and the receiving node grant serial bus access to the sending node or the receiving node having the highest first bus priority in the respective first and second messages.

18. A method, comprising:

assembling a message at a source node, wherein the message includes at least a data ID field for providing a content identifier inherently exhibiting a first bus priority, wherein the content identifier represents a pre-assigned priority of the message content, the message further including a priority field for providing a variable priority, wherein the variable bus arbitration priority is computationally adjustable by the node to change the pre-assigned priority of the message content, 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 a 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 or more 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, and if the variable priorities of the source node and the one or more recipient nodes do not differ, granting access to the serial bus to the source node or the recipient node having the highest first bus priority.

19. 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.

20. The method of claim 19, 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.

21. The method of claim 18, farther comprising dynamically modifying the variable priority based on a condition sensed via the serial bus.

22. The method of claim 21, wherein the condition sensed via the serial bus comprises determining the source node has lost arbitration a predetermined number of times.

23. The method of claim 21, wherein the condition sensed via the serial bus comprises determining that a control range has been exceeded.

24. The method of claim 18, wherein a highest priority value of the variable priority is reserved for a safety-critical situation.