Inspection system with data acquisition system interconnect protocol

• US 20060083257A1
• Filed: 10/20/2004
• Published: 04/20/2006
• Est. Priority Date: 10/20/2004
• Status: Active Grant

• Current Assignee: L-3 Communications Security and Detection Systems Incorporated
• Original Assignee: L-3 Communications Security and Detection Systems Incorporated
• Inventors: Price, John, Sieving, Alan Roy, Karon, James Angelo
• Granted Patent: US 7,664,015 B2
• Time in Patent Office: Days
• US Class Current: 370/444
• CPC Class Codes: H04L 1/16 in which the return channel carries supervisory signals, e.g. repetition request signals
• CPC Class Codes: H04L 12/44 Star or tree networks
• CPC Class Codes: H04L 2001/0092 Error control systems characterised by the topology of the transmission link
• CPC Class Codes: H04L 7/0008 Synchronisation information channels, e.g. clock distribution lines

Abstract

An improved interconnection protocol that is well suited for use in an inspection system or similar modular electronic system. Communication is provided over a network where the electronic modules are nodes, including a root node and multiple remote nodes. The root node and remote nodes are connected through multiple point-to-point synchronous links. The root node and remote nodes are configured to send and receive packets in either a short form or a normal form. Timing between the root node and remote nodes is provided by an external clock distributed by the root node. Each remote node responds to commands with low latency. This protocol allows normal packets to be configured to provide variable payload length, with a maximum payload size that yields a low protocol overhead.

Claims

1. A network comprising:

a) a root node;

b) a plurality of remote nodes, each comprising a receiver, a buffer and control logic; and

c) a plurality of serial communication links interconnecting the root node to each of the remote nodes, each link comprising;

i) at least one line carrying at least two types of packets from the root node to the remote node; and

ii) at least one line carrying packets from the remote node to the root node;

wherein a first type of packet received at the remote node is stored in the buffer and processed by the control logic in order of reception and a second type of packet received at the remote node causes an interrupt to the control logic whereby the second type of packet is processed by the control logic in response to interrupt.

2. The network of claim 1, wherein each link further comprises:

iii) at least one line carrying a clock signal from the root node to the remote node.

3. The network of claim 1, wherein each of the lines comprises a twisted pair.

4. The network of claim 3, wherein each of the serial communication links comprises a CAT-5 cable.

5. The network of claim 4, wherein each of the CAT-5 cables is terminated with an RJ-45 connector.

6. The network of claim 1, wherein a plurality of the remote nodes are connected in a daisy chain configuration.

7. The network of claim 2, wherein the clock signal has a frequency between 20 MHz and 120 MHz.

8. The network of claim 1, wherein the first type of packet and the second type of packet comprise a plurality of fields, and wherein each of the first type of packet and the second type of packet comprises a payload field comprising a plurality of bytes, wherein a maximum number of bytes that may be included in the payload field of the first type of packet is less than a maximum number of bytes that may be included in the payload field of the second type of packet.

9. The network of claim 8, wherein the second type of packet comprises a size field indicating the number of bytes of data in the payload field, wherein a maximum value in the size field is greater than the numbered bytes in the payload field in packets of the first type.

10. The network of claim 9, wherein the second type of packet comprises an address field and the first type of packet does not comprise an address field.

11. The network of claim 8, wherein each of the bytes is transmitted over one of the serial communication links as two nibbles, each represented with a 6 bit code.

12. The network of claim 8, wherein the first and second types of packets each comprise at least two forms of error detection.

13. The network of claim 12, wherein one form of error detection comprises a CRC field in each of the packets.

14. The network of claim 12, wherein one form of error detection comprises a redundant coding scheme.

15. The network of claim 8, wherein packets of the first type of packet comprise a fixed length payload in the payload field and packets of the second type of packet comprise a variable length payload in the payload field.

16. The network of claim 15, wherein the variable length payload has a minimum length of 0 bytes and a maximum length of 65,535 bytes.

17. The network of claim 15, wherein the second type of packet has less than 10 bytes of overhead.

18. A method of operating an electronic system comprising a network, the network comprising a root node and a plurality of remote nodes, the method comprising:

sending packets of a first type and packets of a second type from the root node to a remote node; and

at the remote node, buffering and then processing the packets of the second type, and processing without buffering the packets of the first type.

19. The method of claim 18, wherein receipt of a packet of the first type at the remote node causes the remote node to interrupt processing operations and process the packet of the first type.

20. The method of claim 18, wherein the electronic system comprises an application level, and wherein processing the packets of the first and second types comprises providing information to the application level.

21. The method of claim 18, further comprising:

using, at the application level, information provided by the network as a result of a packet of the first type for timing of an application event.

22. The method of claim 21, further comprising sending packets of the second type from one of the remote nodes remote node to the root node, the packets of the second type comprising a payload containing data acquired during the application event.

23. The method of claim 18, further comprising:

assigning addresses to each of the remote nodes.

24. The method of claim 23, wherein assigning addresses comprises, for each of the remote nodes:

transmitting a request from the remote node to the root node using a packet of the first type;

transmitting an address to the remote node using the packet of the first type; and

transmitting an acknowledgement.

25. A method of operating an electronic system having an application level and a network, the network comprising a plurality of nodes, including a first node and a second node, with each of the nodes having packet processing circuitry that sends packets of a first type over the network in response to commands from an application layer of the electronic system, the method comprising:

sending packets of a second type by the first node to the second node; and

when the first node receives from the application layer a command to transmit a command while transmitting a packet of the second type, interrupting transmission of the second type packet and transmitting a packet of a first type communicating the command.

26. The method of claim 25, wherein upon transmission of the packet of the first type, the first node restarts the transmission of the packet of the second type in its entirety.

27. A method of operating a network having a physical link between at least a first node and a second node, comprising:

providing a plurality of units of information to be transmitted from the first node to the second node;

encoding each of the units of information with a sequence having a number of logical HIGHs and a number of logical LOWs, with the number of logical HIGHs and logical LOWs in each unit being equal; and

transmitting electrical signals representing the sequence of logical HIGHs and LOWs for each of the units over the link, with the electrical signals being AC coupled to the link.

28. The method of claim 27, wherein each of the units is provided with a first number of bits and is encoded with a sequence of logical HIGHs and LOWs with a second number of values in the sequence, the second number exceeding the first number.

29. The method of claim 28, wherein the first number of bits is 4 and the number of values is 6.

30. The method of claim 28, wherein a first plurality of sequences of logical HIGHs and LOWs corresponds to valid units of information and a second plurality of sequences of logical HIGHs and LOWs does not correspond to valid units of information, and wherein the method further comprises performing error checking by determining whether received sequences correspond to valid units of information.

31. The method of claim 28, wherein a first plurality of sequences of logical HIGHs and LOWs corresponds to valid units of information and a second plurality of sequences of logical HIGHs and LOWs does not correspond to valid units of information, and wherein the method further comprises transmitting at least one of the second plurality of sequences of values to identify the start of a packet of information.

32. A data acquisition system, comprising:

a data processor;

a plurality of electronic modules, each acquiring data in response to a command; and

a network interconnecting the plurality of electronic modules and the data processor, the network comprising a root node coupled to the data processor and a plurality of remote nodes, each remote node coupled to one of the electronic modules, the root node and each of the remote nodes having packet processing circuitry adapted to process at least a first type of packet and a second type of packet, the packet processing circuitry including a buffer adapted to store the second type of packet and bypass circuitry for the first type of packet.

33. The data acquisition system of claim 32, wherein the plurality of electronic modules are adapted to detect radiation.

34. The data acquisition system of claim 33, further comprising a radiation source.

35. The data acquisition system of claim 34, further comprising a conveyor oriented such that objects located thereon pass between the radiation source and at least some of the electronic modules.

36. The data acquisition system of claim 35, further comprising a display coupled to the data processor, wherein the display comprises an interface adapted for viewing at least a portion of an object located on the conveyor.

37. The data acquisition system of claim 32, further comprising an external clock signal transmitted from the root node to at least some of the plurality of remote nodes.