Abstract:
Various methods for ensuring compatibility between devices utilizing the IEEE 1394-1995 serial bus standard and new implementations of the standard are disclosed. Methods are disclosed which a allow border nodes to speed filter a Legacy cloud. Methods are disclosed which allow a BOSS node to speed filter a Legacy cloud. 
     A method for ensuring compatibility is disclosed which comprises 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 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.

Description:
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 
     BACKGROUND 
     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 travelling 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 travelling 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 travelling 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 systems 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 S 100 , S 200 , and S 400 , 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, S 100 , S 200 , and S 400 . Initially, when the IEEE 1394-1995 standard was introduced, devices could only communicate at the S 100  rate. Later, devices were introduced that communicated at the S 200  and S 400  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 S 400  data rate, while node # 0  is only capable of communication at the lower S 100  rate. 
     FIG. 3 illustrates the prior art solution of speed filtering on a Legacy bus. FIG. 3 shows root node # 2  transmitting S 400  data in packet P 1  to node # 1 . In the prior art, to prevent node # 0  from receiving the S 400  data that it cannot understand, it is “shielded” from such data by having root node # 2  transmit a null packet P 2  to it. 
     In the FIG. 3 Packet Detail illustration, packets P 1  and P 2  are shown together on a common time axis. Packet P 1  comprises a DP  300 , S 400  data  302 , and a DE  304 . Null packet P 2  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 S 400  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 S 400  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 Sb 1  and a Data Prefix symbol DP 1  are shown as the packet starting symbols. Then, P1394b data bytes B 1  through Bn are transmitted. Data bytes B 1  through Bn may be referred to herein as the payload. Finally, the transmission of data is terminated by transmitting DE symbols DE 1  and DE 2 . 
     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 an “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&#39;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 by 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&#39;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 symbols 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. As a consequence, if the speed is such that the DATA_NULL symbol is less than one symbol duration, then the filtered device would not see the DATA_NULL symbol. 
     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 is 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 . 
     Otherwise, if there are peer Beta devices incapable of communicating at such a speed, then a DATA_NULL will be repeated to devices not capable of receiving a packet of such a speed by the PHY in act  902 . If 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. 
     It is contemplated that the acts that follow will take place for the duration of the higher speed packet. As mentioned above, it is critical to ensure that the filtered Beat device be filtered for at least one symbol duration as measured by the filtered device&#39;s speed rate. Thus, the process in FIG. 9 proceeds to query  904  where it is determined whether the Beta device has been transmitting a DATA_NULL to the filtered device for a period equal to or greater than one symbol duration, again as measure by the filtered device&#39;s speed rate. In a preferred embodiment of the present invention, this determination is accomplished through the use of timers that are set within the Beta device. It is contemplated that this timing may be accomplished through the use of any means, including by way of example the use of mathematical computations or the like. 
     If the result of query  904  is that one symbol duration has elapsed for the filtered device, then the process of FIG. 9 ends. Otherwise, the process moves to query  906 . 
     In query  906 , a loop is set up whereby two conditions are tested. First, it is determined whether the filtered device has been filtered for at least one symbol duration. At the same time, it is determined whether the Beta device has received another packet. The process in query  906  waits until one of these two conditions is met. Whichever condition is met forces the process in FIG. 9 to end. 
     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.