# Patent

## Title
Method and apparatus for ensuring compatibility on a high performance serial bus

## Abstract

A data communications system is disclosed having at least one Legacy cloud coupled to at least one Beta cloud. The system further having at least one BOSS node and at least one border node. A method for ensuring compatibility is disclosed comprising determining when the BOSS node is idle, determining whether the last packet transmitted by any border node was an Alpha format packet if the BOSS node is idle, and unlocking the Legacy cloud if the last packet transmitted by the border node was not an Alpha format packet.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. patent application Ser. No. 10/984,535, filed Nov. 8, 2004 now U.S. Pat. No. 7,050,453, which is a Continuation of U.S. patent application Ser. No. 09/507,120, filed Feb. 17, 2000, now issued as U.S. Pat. No. 6,831,928, both of which are hereby incorporated by reference herein.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to data communications. In particular, the present invention relates to ensuring compatibility on a high performance serial bus system.
2. The Prior Art
Modern electronic equipment has greatly enhanced the quality of our lives. However, as the use of such equipment has increased, so has the need to connect equipment purchased from different manufacturers. For example, while a computer and a digital camera may each be useful when used alone, the ability to connect the digital camera to the computer and exchange information between the two makes the combination even more useful. Therefore, a need was apparent for a serial bus standard that would allow for the connection and communication between such devices.
The IEEE 1394-1995 standard was developed to satisfy this need. This standard revolutionized the consumer electronics industry by providing a serial bus management system that featured high speeds and the ability to “hot” connect equipment to the bus; that is, the ability to connect equipment without first turning off the existing connected equipment. Since its adoption, the IEEE 1394-1995 standard has begun to see acceptance in the marketplace with many major electronics and computer manufacturers providing IEEE 1394-1995 connections on equipment that they sell.
However, as technologies improved, the need to update the IEEE 1394-1995 standard became apparent. Two new standards are being proposed at the time of the filing of this application, herein referred to as the proposed IEEE 1394a, or P1394a standard, and the proposed IEEE 1394b, or P1394b standard. Improvements such as higher speeds and longer connection paths will be provided.
In the discussion that follows, it will be necessary to distinguish between the various standards that are being proposed as of the date of this application. Additionally, it will be necessary to distinguish hardware and packet transmissions that are compatible with the P1394b standard and not earlier standards.
Thus, the term “Legacy” will be used herein to refer to the IEEE 1394-1995 standard and all supplements thereof prior to the P1394b standard. Thus, for example, a Legacy node refers to a node compatible with the IEEE 1394-1995 standard and all supplements thereof up to, but not including, the P1394b standard.
Additionally, packets of data will be referred to herein depending on the context the packets are in. For example, a packet of data that is compatible with the P1394b standard and is traveling through a PHY compatible with the P1394b standard will be referred to as Beta format packets. Packets of data that are compatible with the Legacy standard but are traveling through a PHY compatible with the P1394b standard will be referred to as Legacy packets. Finally, packets of data that are compatible with the Legacy format and are traveling across a data strobe link will be referred to as Alpha format packets.
Furthermore, in the discussion that follows PHYs that are compatible with the P1394b standard may be referred to in various ways, depending upon the context the PHY is operating in and the capability of the PHY. For example, a PHY that has circuitry compatible with the P1394b standard but not any previous standards will be referred to as a B only PHY. Also, a PHY that is compatible with both the P1394b standard and all predecessors and is communicating with only devices compatible with the P1394b standard will be referred to as B PHYs. Finally, a PHY that is communicating with both Legacy devices and devices compatible with the P1394b standard will be referred to as a border device, border PHY, or border node.
Finally, a communications system that has only B PHYs attached will be referred to as a B bus.
Data transmission in Legacy systems
One area that has been improved in the P1394b standard is in the way that data transmission takes place on the bus.
FIG. 1 is a prior art example of a Alpha format data packet 100 according to Legacy specifications. In the IEEE 1394-1995 standard, a data packet will begin with the transmission of a Data Prefix (“DP”) identifier, shown as DP 102 in FIG. 1. Importantly, in the IEEE 1394-1995 standard, a DP must have a duration of no less than 140 nanoseconds (ns), though a DP may be of any greater length.
Typically, a DP is followed by the transmission of clocked data, known as the payload, shown as clocked data 104 in FIG. 1. On a Legacy bus, the payload will be clocked at a rate of 100 Megabits per second (Mb/s), 200 Mb/s, or 400 Mb/s. These data rates are known as S100, S200, and S400, respectively.
Finally, the payload is followed by a Data End (“DE”), shown as DE 106 in FIG. 1. In the IEEE 1394-1995 standard, a DE must be at least 240 ns in length.
As is appreciated by one of ordinary skill in the art, the Legacy specifications thus a timer-based system, where data transmission begins and ends according to a fixed timer.
Compatibility issues in Legacy systems
As mentioned above, there are three clocked data rates present in Legacy systems, S100, S200, and S400. Initially, when the IEEE 1394-1995 standard was introduced, devices could only communicate at the S100 rate. Later, devices were introduced that communicated at the S200 and S400 rates.
One problem that occurred in the prior art was how to insure compatibility between the various devices on the market that were communicating at these different rates.
FIG. 2 illustrates such a compatibility problem. FIG. 2 has three nodes, nodes #0, #1, and #2. Node #2, the root node in this example, wishes to communicate with node #1. As is indicated in FIG. 2, nodes #1 and #2 are capable of communicating at the S400 data rate, while node #0 is only capable of communication at the lower S100 rate.
FIG. 3 illustrates the prior art solution of speed filtering on a Legacy bus. FIG. 3 shows root node #2 transmitting S400 data in packet P1 to node #1. In the prior art, to prevent node #0 from receiving the S400 data that it cannot understand, it is “shielded” from such data by having root node #2 transmit a null packet P2 to it.
In the FIG. 3 Packet Detail illustration, packets P1 and P2 are shown together on a common time axis. Packet P1 comprises a DP 300, S400 data 302, and a DE 304. Null packet P2 comprises a DP 306, and a DE 308. As is appreciated by one of ordinary skill in the art, the null packet accomplishes its shielding by extending the DP for the amount of time required to send S400 data 302. As is known by those of ordinary skill in the art, on a Legacy bus all nodes must remain synchronized in their interpretation of idle time. Thus, the null packet effectively ‘busies’ node #0 while root node #2 transmits S400 data to node #1 and thus shields node #0 from speeds it cannot understand.
Data transmission in P1394b
FIG. 4 is a representation of the prior art data packet structure according to the P1394b standard. As is known by those of ordinary skill in the art, P1394b utilizes a packet structure that is scaled to speed unlike the fixed timer system utilized in Legacy standard. Specifically, the packet structure in P1394b is based upon symbols, rather than the fixed intervals found in the Legacy standard.
In FIG. 4, a typical prior art packet 400 of P1394b data is shown. As is known by those of ordinary skill in the art, a data packet begins in P1394b with the transmission of at least two packet starting symbols. In this example, a Speed Code symbol Sb1 and a Data Prefix symbol DP1 are shown as the packet starting symbols. Then, P1394b data bytes B1 through Bn are transmitted. Data bytes B1 through Bn may be referred to herein as the payload. Finally, the transmission of data is terminated by transmitting DE symbols DE1 and DE2.
Compatibility Problems between P1394b and Legacy Nodes and Clouds
FIG. 5 shows a data communications system comprising both P1394b and Legacy devices. This type of system will be referred to herein as a “hybrid” system. FIG. 5 shows a Legacy node #0 connected to Legacy node #4, forming what is known as a “Legacy cloud” of Legacy nodes.
Legacy node #4 is connected to border node #3. Border node #3 is connected to B PHYs #1 and #2, forming what is known as a “Beta cloud” of border and B PHYs.
As mentioned above, the data prefix in IEEE 1394-1995 is at least 140 ns in length, and the data end is 240 ns. Therefore, the smallest Legacy packet, including the mandatory idle time that must follow, is at least 400 ns in length. As is appreciated by those of ordinary skill in the art, the problem of compatibility arises because this amount of time can be greater than an entire data packet in P1394b.
Therefore, in order for Beta devices to communicate with each other, any Legacy devices must at the same time be protected from receiving Beta packets. As can be seen from FIG. 5, this protection must be accomplished by the border node, since it is the node connecting the Legacy and Beta clouds together.
Currently, there is no provision for allowing a Beta cloud to communicate within itself while connected to a Legacy cloud.
Therefore, there is a need for a protocol that allows a border node to manage Legacy nodes while communication with a Beta cloud occurs and does not affect the delivery of Alpha format or Legacy packets.
Finally, there is a corollary need for a protocol to speed filter slower beta devices from higher speed packets within a beta cloud.
BRIEF DESCRIPTION OF THE INVENTION
The invention satisfies the above needs. The present invention relates to a method and apparatus for ensuring compatibility in a high performance serial bus.
A method for ensuring compatibility is disclosed, comprising: waiting until the border node receives a packet; issuing a data prefix packet by the border node into the Legacy cloud when the border node receives a packet; determining whether the border node has received or transmitted a Legacy packet; and appending the Legacy packet onto the end of the data prefix and transmitting the Legacy format packet into the Legacy cloud if the border node has received or transmitted a Legacy packet.
A method for ensuring compatibility is disclosed, comprising: determining when the BOSS node is idle; determining whether the last packet transmitted by any border node was an Alpha format packet if the BOSS node is idle; and unlocking the Legacy cloud if the last packet transmitted by the border node was not an Alpha format packet.
A method for ensuring compatibility is disclosed, comprising: determining whether the last packet transmitted or received by the border node was an Alpha format packet; arbitrating for control of the bus if the last packet transmitted or received by the border node was not an Alpha format packet; determining whether border node's arbitration request was granted; repeating last packet received if the arbitration request was not granted and returning back to the step of determining whether the last packet transmitted or received by the border node was an Alpha format packet; and unlocking the Legacy cloud if the arbitration request was granted.
A method for ensuring compatibility is disclosed, comprising: determining whether the B PHY desires to communicate at a speed on a bus having a peer device not capable of communicating at the speed; and speed filtering the peer device if the B PHY determines that the peer device cannot communicate at the speed.
Various data packets and methods for transmitting data packets are also disclosed to satisfy the needs discussed herein.



BRIEF DESCRIPTION OF THE DRAWING FIGURES
FIG. 1 is a prior art Alpha Format Packet example.
FIG. 2 is a prior art Legacy Compatibility example.
FIG. 3 is a prior art Legacy Speed Filtering example.
FIG. 4 is a prior art P1394b Packet format example.
FIG. 5 is a prior art Data Communications System having both P1394b and Legacy devices.
FIG. 6 Is A Flowchart For Managing Legacy Devices By A Border Node According To The Present Invention.
FIG. 7 Is A Flowchart For Unlocking Legacy Devices By A BOSS Node According To The Present Invention.
FIG. 8 Is A Flowchart For Locking And Maintaining Lock Status By A Border Node According To The Present Invention.
FIG. 9 Is A Flowchart For Speed Filtering Beta Devices According To The Present Invention.



DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Persons of ordinary skill in the art will realize that the following description of the present invention is illustrative only and not in any way limiting. Other embodiments of the invention will readily suggest themselves to such skilled persons having the benefit of this disclosure.
The present invention relates to data communications. More particularly, the present invention relates to a method and apparatus for an arbitration and fairness protocol on a serial bus. The invention further relates to machine readable media on which are stored embodiments of the present invention. It is contemplated that any media suitable for retrieving instructions is within the scope of the present invention. By way of example, such media may take the form of magnetic, optical, or semiconductor media.
The present invention relates to data structures and the transmission of such data structures. It is contemplated that the present invention may be embodied in various computer and machine readable data structure. Furthermore, it is contemplated that data structures embodying the present invention will be transmitted across computer and machine readable media.
The present invention may be described through the use of flowcharts. Often, a single instance of an embodiment of the present invention will be shown. As is appreciated by those of ordinary skill in the art, however, the protocols and procedures described herein may be repeated continuously or as often as necessary to satisfy the needs described herein. Accordingly, the representation of the present invention through the use of flowcharts should not be used to limit the scope of the present invention.
The present invention further relates to devices that embody the P1394b standard. By way of example, such devices may include those typically used in an audio/video entertainment system, such as home theater receivers, DVD players, computers, or hand-held devices such as cameras and the like. The devices may also include those industrial in nature, such as test and measurement equipment, professional audio/video recording devices, as well as system control or robotic devices found in an industrial environment.
The invention also relates to nodes and physical computers, such as state machines. The present invention may be embodied in any collection of nodes linked together through a bus. Typically, each device connected to the bus will also have one corresponding node physical layer controller embedded therein. However, a given device may have more than one node, and therefore it follows that one device may have more than one connection to more than one bus. For the discussion that follows, the examples will show the typical situation were one node corresponds to one device.
Each node may communicate to other nodes in an P1394b-compatible system though links. Typically, a cable is used for a link, as is provided for in the P1394b standard. However, any communication means may be employed. By way of example, an infrared, RF, or other wireless system may be used, as well as an optical system.
Typically, a link is coupled to a node through a port. A port transmits and receives messages and data between the node and link. As is known by those of ordinary skill in the art, each node may have more than one port.
Border Node Behavior
FIG. 6 is a flowchart of one embodiment of the present invention. The process begins with query 600. In query 600, the border node listens for a data packet. If there is no data packet received, the border node loops, waiting for a data packet.
When the border node receives a data packet, it then sends a DP indication to the Legacy cloud in act 602. This will “lock up” the Legacy cloud. Now that the Legacy cloud is locked up, devices may transmit P1394b data within the Beta cloud without affecting the Legacy cloud.
Referring still to FIG. 6, the border node will wait to receive or transmit a Legacy packet to appear, as shown in query 604. When a Legacy packet appears, the border node will append the Legacy data onto the existing DP along with a DE, and transmit the packet to the Legacy cloud in act 606, thus unlocking the Legacy cloud.
FIG. 7 is a flowchart of another preferred embodiment of the present invention. In FIG. 7, the BOSS node will determine whether it is idle in query 700. When the BOSS node becomes idle, it will then determine whether the last packet transmitted or received by any border node was an Alpha format packet in query 702. It is contemplated that this determination may be done by any means. For example if a B PHY is BOSS and it last sent a Beta format packet, then it knows that packet transmitted or received by a border node was not an Alpha format packet.
If the was determined in query 702 that the last packet transmitted or received by any border node was not an Alpha format packet, the border node will then unlock the Legacy cloud in act 704. It is contemplated that various means may be used to unlock a Legacy cloud. By way of a non-limiting example, in one preferred embodiment, the Legacy cloud is unlocked by having the BOSS node transmit a null packet to the Legacy cloud. However, any means for unlocking a Legacy cloud is within the scope of the present invention.
FIG. 8 is a flowchart for locking and maintaining lock status by a border node according to the present invention. The process begins in query 800 by the border node determining whether the last packet transmitted or received by the border node was an Alpha format packet. If the border node last transmitted or received an Alpha format packet, the process ends.
Referring still to query 800 of FIG. 8, if the last packet transmitted by the border node was not an Alpha format packet, then the Legacy cloud is still locked up. The border node will first arbitrate for control of the bus in act 802.
The border node will then determine whether its arbitration request was granted in query 804. If it was, then the border node will then unlock the Legacy cloud in act 806. As mentioned above, there are many ways to unlock a Legacy cloud. By way of a non-limiting example, in one preferred embodiment, the Legacy cloud is unlocked by having the border node transmitting a null packet to the Legacy cloud. However, any means for unlocking a Legacy cloud is within the scope of the present invention.
If the border node's arbitration request was not granted in query 804, then the border node will repeat the received packet into the cloud in act 808, and the process will return the beginning in query 800.
Speed filtering in P1394b
The present invention defines a new P1394b symbol known as a DATA_NULL. When a beta packet is to be sent out at a speed that is greater than the port speed of a peer device such as a receiving beta node, then a DATA_NULL will be sent to that node instead as method of speed filtering.
In a preferred embodiment of the present invention, the DATA_NULL is defined such that the node is left in the arbitration request phase, which allows DATA_NULL symbol
 to be deleted if necessary, but caution is taken to ensure that at least one symbol is seen by the slower device such that bus timers are reset. This would occur, by way of example, if the high speed packet is very fast compared to the speed of the speed filtered device. If the speed is such that the DATA_NULL symbol is less than one symbol duration, then the filtered device will not see the DATA_NULL symbol. But if it does get seen by the filtered device, then this signifies that the bus is occupied, and the bus timers should be reset. <Comma, will-would>
In another preferred embodiment of the present invention, the result of the above process is such that the filtered device is held in an arbitration request phase until the Beta device is finished communicating.
Furthermore, unlike the Legacy speed filtering method above in the prior art section above, the present invention allows to the speed filtering duration to be scalable to symbols, and is therefore not subject to the Legacy 400 ns packet time.
Also, the DATA_NULL symbol can be used as a DENY indication within the beta cloud. This use also has the advantage of not committing the cloud to a Legacy packet until necessary.
Thus, when used as a DENY indication, a node receiving the DATA_NULL will repeat it out of all ports at the appropriate speeds. If a Legacy packet is eventually sourced, then the accompanying DP will alert the beta nodes and the process described above in the border node discussion will take place.
If the packet turns out to be a beta packet, then the node will repeat the packet to only those beta nodes capable of receiving a beta packet of that speed.
FIG. 9 is a flowchart of speed filtering Beta devices. In query 900, a B PHY will determine whether it desires to communicate on a bus where there are peer Beta devices that are not capable a communicating at such a speed. If there is, then the DATA_NULL will be repeated to devices not capable a receiving a packet of such speed by the B PHY in act 902.
When a border node receives a DATA_NULL packet, it will issue a DP into the Legacy cloud in accordance with the border node protocol as described above.

    
    
        <set timers, calculate math>
    
    


While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art that many more modifications than mentioned above are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the appended claims.

## Claims

1. A non-transitory machine-readable medium containing instructions which when executed by a computer ensure compatibility in a data communications system compliant with the IEEE-1394b standard and having at least one B PHY, by performing the acts of:
determining whether the B PHY desires to communicate at a speed on a bus having a peer device not capable of communicating at said speed; and
speed filtering said peer device if said B PHY determines that said peer device cannot communicate at said speed, said speed filtering comprising sending a designated symbol to said peer device.

2. The non-transitory machine-readable medium of claim 1, wherein said designated symbol comprises a data nullification symbol.

3. A computerized node apparatus capable of communicating with other computerized devices, said node apparatus comprising a non-transitory machine-readable medium containing instructions which when executed by a computer ensure compatibility in a data communication system implementing a serial bus protocol by:
receiving a packet at said node apparatus;
determining whether the received packet is to be sent out at a speed that is greater than a port speed of a peer device; and
transmitting a speed filtering symbol to said peer device if it is determined that said speed is greater than said port speed of said peer device.

4. The node apparatus of claim 3, wherein said packet comprises a beta packet, and said serial bus protocol comprises an IEEE-1394b compliant protocol.

5. The node apparatus of claim 4, wherein said speed filtering symbol comprises a data null symbol.

6. The node apparatus of claim 4, wherein a duration associated with said speed filtering is scalable based at least on one or more symbols.

7. The node apparatus of claim 4, wherein a duration associated with said speed filtering is not restricted to a predetermined value.

8. The node apparatus of claim 3, wherein said peer device comprises at least a portion of a beta cloud.

9. The node apparatus of claim 3, wherein both said node apparatus and said peer device comprise beta devices.

10. The node apparatus of claim 3, wherein said speed filtering symbol causes said peer device to be held in an arbitration process for at least a period of time.

11. The node apparatus of claim 3, wherein said speed filtering symbol causes said peer device to be held in an arbitration process at least until said node apparatus has completed transmission of said packet.

12. A machine-readable apparatus having a non-transitory machine-readable medium containing instructions which when executed by a computer perform a method of speed filtering comprising:
determining whether a speed associated with a packet to be transmitted on a local port exceeds the operating speed of a peer port; and
filtering communications sent over a bus between said local port and said peer port if it is determined that said peer port cannot communicate at said speed, said filtering comprising sending a designated symbol to said peer port, said symbol at least in part causing said filtering.

13. The machine-readable apparatus of claim 12, wherein said designated symbol comprises a data nullification symbol.

14. A method of ensuring compatibility in a data communication system implementing a serial bus protocol, said method comprising:
receiving a packet to be transmitted via a node apparatus;
determining whether the packet received is to be transmitted at a speed that is greater than a speed associated with a port receiving said packet; and
transmitting a speed filtering symbol to said port if it is determined that said speed is greater than said speed of said port.

15. The method of claim 14, wherein said packet comprises a beta packet, and said serial bus protocol comprises the IEEE-1394b standard.

16. The method of claim 14, wherein a duration associated with said speed filtering is scalable based at least on one or more symbols, said one or more symbols including said speed filtering symbol.

17. The method of claim 14, wherein a duration associated with speed filtering resulting from said speed filtering symbol is not restricted to a predetermined value.

18. The method of claim 14, wherein said speed filtering symbol causes a device associated with said receiving port to be held in an arbitration process for at least a period of time.

19. The method of claim 14, wherein said speed filtering symbol causes a device associated with said receiving port to be held in an arbitration process at least until said node apparatus has completed transmission of said packet.

20. The method of claim 14, wherein said receiving port is located at a peer device.

21. A method of speed filtering in a serial communications system, the method comprising:
determining whether a speed associated with a packet to be transmitted on a local port exceeds the operating speed of a peer port, and if so;
filtering communications sent over a serial bus between said local port and said peer port with respect to at least one speed-related parameter, said filtering comprising sending a designated symbol to said peer port, said symbol causing said peer port to be held in an arbitration phase for at least a period of time.

22. The method of claim 21, wherein said designated symbol comprises a data nullification symbol.

23. A method of operating a serial bus communications system, the method comprising:
communicating to a peer device the operating speed of a local port; and
receiving a designated symbol in response to a determination that the operating speed of said local port is incompatible with the speed of one or more packets to be transmitted by said peer device to said local port, said designated symbol causing filtering of at least a portion of the communications between said peer device and said local port.

24. The method of claim 23, wherein said filtering comprises filtering for at least the duration of said one or more packets based on said speed of said local port.

25. A node apparatus capable of communicating with a peer device over a serial bus, said node apparatus comprising a non-transitory machine-readable medium containing instructions which when executed by a computer enforce speed compatibility in a data communication system by at least:
communicating to said peer device the operating speed of a local port of said node apparatus; and
receiving a designated symbol in response to a determination that the operating speed of said local port is incompatible with the speed of a packet to be transmitted by said peer device to said local port, said designated symbol causing said node apparatus to be held in a data arbitration state for a period at least equal to a duration of said packet, said packet duration being based on said local port operating speed.

26. The node apparatus of claim 25, wherein said packet to be transmitted by said peer device comprises a beta packet, and said serial bus is compliant with the IEEE-1394b Standard.

27. The node apparatus of claim 26, wherein said period is scalable based on the number of symbols transmitted.

28. The node apparatus of claim 25, wherein said peer device comprises at least a portion of an IEEE-1394 beta cloud.