Abstract:
A detector and method for detecting Wakeup-On-LAN (WOL) frames in which the Wakeup field can start on a two byte word boundary (even) or in the middle of the two byte word (odd). The orientation (even/odd) of the WOL and destination address (DA) fields are determined and a first or second two byte process, depending on the orientation, is selected to analyze the frame to determine if it is valid.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a Wakeup-On-LAN (WOL) detector and a method for use in local area networks in which specific network client station(s) can be awakened from a power down or sleeping state by receipt of a packet addressed to the specific station(s). The architecture selected for implementing the WOL function permits the WOL pattern to be inserted in a variety of locations in the pay load field of a frame within which it is transmitted. This allows the WOL pattern to start in a byte which may be either aligned with or not aligned with a data word boundary. 
     In order to improve performance, WOL frames are processed in two byte words using a sixteen bit internal bus. No problem exists when the WOL pattern starts on a word boundary. However, if the pattern starts in the middle or odd byte of a two byte word, a conventional two byte detection process will not work. 
     SUMMARY OF THE INVENTION 
     The invention contemplates a detector responsive to a received data frame which includes as part of its payload, a first signal F . . . F for indicating a wakeup condition and a second signal DA . . . DA for identifying a specific device. A detector responsive to the frame and the F . . . F signal provides a control signal indicating the relative position of the DA . . . DA signal with respect to the F . . . F signal. The DA . . . DA signal is handled by a first processing means when the relative position of the DA . . . DA signal and the F . . . F signal are in a first state and by a second processing means when the relative position is not in the first state. If either processing means detects a valid DA signal, a wakeup condition is identified. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is diagrammatic representation of the frame structure of a WOL packet. 
     FIG. 2 is a diagram of a detector constructed according to the invention. 
     FIG. 3 is a flow chart illustrating the operation of the detector illustrated in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A typical ethernet frame is illustrated in FIG. 1 for the purpose of describing the invention. Other network protocols could have been selected since the invention is not limited to any particular network protocol and functions in the same manner regardless of the protocol selected. 
     The frame includes a seven byte preamble, followed by a one byte start delimiter SD. This is followed by six byte destination and source address DA and SA fields. A two byte length field LEN follows the six byte SA field. Two variable length fields LLC and TCP/IP follow the LEN field and precede the conventional WOL pattern. A variable length pay load PL and a fixed length CRC fields complete the frame. The WOL pattern includes six byte header of x′FF followed by sixteen six byte destination addresses DA. 
     Word and byte boundaries can be established reliably from the position of the SD field. However, since the LLC and the TCP/IP fields can have a variable length, it is impossible to predict in advance on what boundary the WOL field will start. This presents a problem if efficient two byte processing is to be used to reliably detect the complete WOL pattern. 
     The two situations presented in a two byte word structure are illustrated in the Figure. In one instance (even), all six bytes of the address (DA 0 -DA 5 ) are contained in three consecutive words which immediately follow the last two bytes of x′FF of the WOL header and are easily available to two byte processing. 
     In the other instance (odd), the first byte DA 0  of the first iteration of the address DA is in the same word as the last byte of x′FF of the WOL header, and the last byte DA 5  is in the same word as the first byte DA 0  of the next iteration of the destination address DA. How these different situations are handled in a two byte process is described below in connection with the description of FIGS. 2 and 3. 
     In FIG. 2, the receive data is stored in a receive frame buffer  20 . It is also selectively applied to byte storage register R 0 . Byte storage registers R 0 -R 6  can be loaded from the receive frame buffer RO. In addition, the contents of byte storage R 6  can be transferred to byte storage register R 0 . The movement and storage of data is under program control and will become apparent with the description of FIG.  3 . 
     A wakeup header and address comparator  21  compares, under program control of a wakeup detection state machine  22 , the contents of the registers R 0 -R 6  to stored values  23  of the WOL header and  24  of the address DA. As previously described, these include the six contiguous bytes of x′FF and the sixteen contiguous six byte DAs. An even/odd detector  25  responsive to start of frame (SOF) and byte boundary signals, from sources not illustrated since these are conventional signals used in the communications art, provides an even or odd output to the state machine  22 . 
     Even/odd detector  25  need be nothing more than a bistable device set to the odd state upon the simultaneous occurrence of SOF and a byte boundary and toggled to the other state (even) upon the next byte signal. When comparator  21  detects the sixth consecutive byte of x′FF, it signals WOL header detect to detector  25 . At this time, detector  25  signals the state machine  22  of the current state of the detector (either odd or even). 
     As comparator  21  detects proper DAs, it indicates a successful match to the state machine  22  and increments a wakeup counter  26 . Each time that a match is indicated, the state machine checks the value of counter  26 . If it is sixteen, it issues wakeup detect and interrupt signals. 
     In FIG. 3, the program idles waiting for a WOL header detect. Once the header is detected, the program looks to see if the WOL header boundary is odd or even. If the boundary is odd, it branches to a first process  31 . If the boundary is even, it branches to a second process  32 . 
     If branch  32  is selected, the program loads the two bytes following the last x′FF byte in register R 0  and R 1 . The next two bytes are loaded in registers R 2  and R 3 , while the following two bytes are loaded in registers R 4  and R 5 . 
     After the six bytes have been loaded, the contents of registers R 0 -R 5  are compared to the address value DA. If the comparison is successful, the counter  26  is incremented and checked to see if has reached a count of sixteen. 
     If the count of sixteen has been reached, the process ends with the signalling of the WOL detect and the issuance of the interrupt previously described. If the count of sixteen is not reached, the process loops back and repeats until a count of sixteen is reached or until a non-match is found, in which case, the process terminates and waits for detection of a WOL header. 
     If branch  31  is selected because detector  25  indicates that the boundary is odd, the program loads the data byte following the sixth x′FF byte in resister R 0 . The next two data bytes are loaded in registers R 1  and R 2 . The following two bytes are loaded in registers R 3  and R 4  and the next two bytes are loaded in registers R 5  and R 6 . At this time, the contents of registers R 0 -R 5  are compared to the WOL address DA. If the compare is successful, the contents of register R 6  are moved to register R 0  and the program loads the next two bytes in registers R 1  and R 2 . 
     If all of the comparisons are successful, the program will follow the truncated loop fifteen times. After each match and move, the WOL counter  26  is incremented and checked as previously described in connection with the description of path  32 . 
     While only a single implementation of the method has been disclosed, it will be apparent to those skilled in this art that other implementations of the method disclosed in the single embodiment are possible without departure from the spirit and scope of the invention.