Patent Document

BACKGROUND OF THE INVENTION 
     This invention relates to a method and apparatus for debugging faults occurring in a router or other network device and more particularly to compressing core file and storing the compressed core file into an internal flash memory. 
     Network servers and other types of network devices often experience unrecoverable faults. One example of an unrecoverable fault occurs when a routine writes an invalid address value into core memory. When a process tries to access the illegal address value, a fault occurs. For example, a process may request a memory address for a status register used for conducting a direct memory access (DMA) operation. If the memory address is invalid, a fatal error occurs when the process attempts to access the memory address, which causes the router to reset. 
     Viewing core files is vital to resolving fatal fault errors. A core file is essentially a copy of DRAM which contains the program, program pointers, program variables, etc. The core file provides a snap-shot of the router at the time the fault occurred. DRAM is used to meet performance requirements of the system and since the contents of the DRAM are destroyed after a reset operation, the core file must be downloaded to another storage device. Routers can be equipped with some flash memory. However, due to the cost of flash memory, the flash memory is not large enough to hold all DRAM contents. Thus, the core file must be downloaded to an external server connected to the router through a local area network (LAN). The core file can then be analyzed by an engineer from a computer or workstation to identify the source of the fault. 
     The problem with copying a core file to an external device is that the fault condition causing the router to shutdown may be caused by a process that must be operational in order to download the core file. For example, the fault may be caused by a software error with a network protocol or LAN media drivers. If these network interface processes are not operational, the core file cannot be successfully downloaded to an external network device. Thus, in the past, a special image had to be created in order to investigate the fault. The special image is produced by modifying operating code to print out specific identified information before the fault occurs. Generating special images to locate faults requires a large amount of trial and error which is extremely time consuming. Alternatively, the router is taken out of production so that the current content of the main memory can be analyzed with a ROM monitor. 
     Accordingly, a need remains for a faster more reliable way to save core file after a fault condition occurs in a network device. 
     SUMMARY OF THE INVENTION 
     A network device, such as a router or switch, downloads a core file into a local flash memory. In order to increase storage capacity, the core file is compressed before being dumped into the local flash memory. The flash memory is local and internal to the network device. Because network interface elements do not have to be functional for a successful core download, the core download is faster and more reliable than existing download techniques. 
     In one embodiment, the network device comprises a router having a CPU for controlling packet processing operations. DRAM is used for a main memory and its contents constitutes the core file. Network interface elements are coupled between the CPU and different external networks. The network interface elements process and route the packets received from the external networks. The core file is downloaded from the main memory to local flash memory independently of these network interface elements. 
     During the shutdown routine, interrupts are disabled for any processing elements, such as the network interface elements, that are not needed to perform the core download. Thus, the CPU is not interrupted by routines that could generate additional fault conditions. Because these processing elements are disabled, the DRAM contents cannot be modified by other processes that might be operating after the fault condition. Thus, the core file will more accurately represent a snapshot of the system at the time the fault condition occurred. 
     In one embodiment of the invention, the CPU downloads the core file to the same local flash memory used for storing the router operating routine and the router shutdown routine. Router platforms may contain more than one flash memory device and different flash memory configurations. The network device can also be configured by a user to download all or part of the core file into one or more of the different flash memory devices used in the specific platform. 
     In order to increase download capacity, each byte of the core file is compressed using a standard compression routine. The compressed core file is written into a temporary buffer in main memory. Once the temporary buffer is full, the contents of the buffer are downloaded into the local flash memory. 
     The router is coupled to a network server through a LAN. The router is reset after completing the core download. The server uses a file transfer operation to access the router and read the core file from local flash memory. The core file is then analyzed to determine the state of the router when the shutdown event occurred. 
     The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment of the invention which proceeds with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a network device according to one embodiment of the invention. 
     FIG. 2 is a detailed diagram of processing elements in the network device shown in FIG.  1 . 
     FIG. 3 is flow diagram showing how the network device operates according to the invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a network device  12  is shown in dashed boxes  40  and  41  and is coupled to a LAN  25 . A network device is defined as any system that processes data or communicates through a network. In one embodiment of the invention, the network device  12  comprises a router that processes and transfers network packets to and from different external devices on different networks or buses. A server  26  is coupled to the router  12  through the LAN  25 . The router  12  includes a CPU  14  coupled through an internal bus  13  and a system arbiter  16  to a main memory  18 . The main memory  18  comprises a Dynamic Random Access Memory (DRAM). Multiple memory devices are coupled to bus  13  and include a flash/Read Only Memory (ROM)  20  used for router bootup, an Electrically Erasable Read Only Memory (EEROM)  21  used for configuring the router  12 , and flash memories  22  and  24  used for storing router routines. A PCMCIA card  42  connects the router  12  to PCMCIA compatible devices (not shown). 
     Multiple network interface elements are shown in dashed box  40  and are used to connect the router  12  to different networks. In the example shown in FIG. 1, the network interface elements  40  include a packet memory arbiter  46  that arbitrates access to a packet memory  44  between an Ethernet or token ring controller  50  and a serial bus controller  54 . A LAN media interface  52  is coupled between LAN  25  and controller  50 . Serial interfaces  32  and  34  are coupled between serial lines (not shown) and controller  54 . 
     Three slots  59  are connected to data bus connections  55 , a Direct Memory Access (DMA) bus  57  and a Time Division Multiplex (TDM) bus  39 . Telephone line interface cards and modem cards (not shown) are coupled to the slots  59 . Calls received by the telephone line interface card are coupled to the modems through the TDM bus  39  or sent over the DMA bus  57  to the packet memory arbiter  46 . A console  28  accesses the internal bus  13  through a DUART  27 . Other devices access the processing elements in router  12  through an auxiliary port  30  also coupled to the DUART  27 . The network interface elements  40 , CPU  14  and internal memory devices are referred to generally as processing elements. 
     The general operation of the processing elements described in FIG. 1 are known to those skilled in the art and are therefore not described in further detail. One router using the architecture shown in FIG. 1 is the Model No. 5200 router manufactured by Cisco Systems, Incorporated, 170 West Tasman Drive, San Jose, Calif. 
     Referring to FIG. 2, the CPU  14  includes an interrupt handler  60  that receives interrupt requests from the different processing elements in the router  12 . The interrupt handler  60  jumps to different routines that service the interrupt requests made by the different processing elements. Interrupt handlers are well known and are, therefore, not described in further detail. The main memory  18  stores the information that constitutes the core file for the router  12 . Core file  61  includes the values of stack pointers, routine variables, the last operating instruction, values set by the last operating instruction, status register addresses, program counters and any other data stored in the main memory  18 . 
     The local flash memory  22  stores a system image that includes operating routines  62 , a shutdown routine  64 , a compression routine  66  and a flash core copy routine  67 . The operating routines  62  include bootup routines, routing protocols, device drivers, configuration routines, etc. and any other routines used by the router to process data. The CPU  14  starts the shutdown routine  64  after detecting a shutdown event. The shutdown routine  64  uses the flash core copy routine  67  to download the contents of main memory  18  to local flash memory  22 . The flash core copy routine  67  also calls the compression routine  66  that compresses the contents of main memory  18  before being downloaded to local flash memory  22 . The boot flash memory  24  contains a boot program  65  used by the router  12  to boot the operating routine  62  after a reset. The flash core copy routine  67  can alternatively copy part of the core file  61  into a portion of the boot flash memory  24  (core file #2). 
     During initial configuration of the router  12 , space is preallocated in main memory  18  for a temporary buffer and memory required for compression routines. If space in main memory  18  is allocated to other processes, the CPU  14  might not be able to successfully allocate space in main memory  18  for the temporary buffer when a shutdown event occurs. By preallocating space in main memory  18 , the flash core copy routine  67  is assured of having sufficient space for compressing and downloading core file  61 . 
     Because volatile DRAM is used for the main memory  18 , the contents of the main memory  18  are lost any time the router  12  is reset. Shutdown events causing a reset occur for any one of a variety of software or hardware faults. For example, a shutdown event occurs when a process loads an invalid address into main memory  18 . When another process tries to use the invalid address, a bus error occurs causing the interrupt handler  60  to call the shutdown routine  64 . 
     If the shutdown routine attempts to download the core file  61  to server  26  (FIG. 1) via a FTP command, the network interface routine used to conduct the FTP operation may be the same routine causing the fault. The CPU  14  would then be unable to successfully download the core file  61  to server  26 . 
     The flash core copy routine  67  according to the present invention solves this problem by downloading the core file  61  to non-volatile local flash memory  22 . Thus, the contents of the core file  61  will not be destroyed when the router  12  is reset. Because the flash core copy routine  67  downloads the core file to local memory, operational status of network interface routines and devices will not affect the core file download process. 
     The flash core copy routine  67  disables interrupts for all processing elements in the router  12 , other than those processing elements used for downloading the core file  61  into local flash memory  22 . For example, the CPU  14  has multiple levels of interrupt priority. When a shutdown event occurs, the CPU  14  is brought up to a higher interrupt level ignoring interrupts at lower levels. Disabling interrupts keeps the CPU  14  from having to service requests generated by interface elements  40  while downloading the core file  61  into local flash memory  22 . 
     Because other interrupts are disabled, the shutdown routine is not disrupted by the interface elements  40  or other processes. If not disabled, the data in main memory  18  could continue to be modified by the interface elements  40  after the shutdown event. By disabling all unnecessary processing elements, the core file provides a more accurate snapshot of the system at the time the system crash occurred. 
     FIG. 3 describes how the flash core copy routine  67  downloads the contents of main memory  18  into local flash memory  22  according to the invention. The CPU  14  in step  70  runs a standard boot routine  65  in ROM/FLASH memory  20  that boots an operating routine. Step  72  runs the operating routine. After an instruction is completed in the operating routine, the CPU  14  checks for interrupts from any one of the processing elements in the router  12 . If an interrupt request is detected, the CPU  14  services the interrupt then continues running the operating routine in step  72 . 
     If a fatal error occurs in decision step  74 , the CPU  14  first stores the address location of the operating routine on a program stack pointer. The address pointer for the shutdown routine  64  is read by the CPU  14 . In step  76 , the shutdown routine  64  calls the flash core copy routine  67  which disables the interrupts for the network interface elements  40  and any other processing elements that are not needed to download the contents from main memory  18  to local flash memory  22 . 
     The flash core copy routine  67  reads 1 byte from the DRAM  18  in step  78 . Step  80  uses the compression routine  66  to compress and store the compressed byte from DRAM  18  into the temporary buffer in main memory  18 . If the temporary buffer is full in decision block  82 , the compressed data in the temporary buffer is downloaded into the local flash memory  22  in step  84 . Any standard compression routine, such as compression routines using a standard hash algorithm, can be used to compress the core file. One hash based compression routine is explained in U.S. Pat. No. 4,558,302 to Welch. 
     After the temporary buffer is downloaded into flash memory in step  84 , or if the temporary buffer is not full in decision step  82 , decision step  86  determines whether there are any more bytes in the main memory DRAM  18 . If all bytes of the main memory  18  have been compressed, any remaining compressed data in the temporary buffer is downloaded into local flash memory in decision step  88 . If there is more data in main memory  18 , decision step  86  reads the next byte in step  78 . 
     The compressed core file  61  can be loaded into the same local flash memory  22  that stores the operating routine  62  and the shutdown routine  64 . Part or all of the compressed core file can also be stored in boot flash memory  24 . If there is insufficient space in local flash memories  22  and  24 , the flash core copy routine  67  stores as many 4K blocks of compressed core file  61  as possible. The remainder of the core file  61  is then downloaded word by word until there is no more space available in the local flash memories. After the compressed core file  61  is downloaded into local flash memory  22 , and possibly flash memory  24 , the router  12  is reset in step  90 . 
     Usually after the router  12  is reset, the previous fault condition causing the shutdown no longer exists. The compressed core file  61  in local flash memory  22  can then be transferred over LAN  25  using an internet protocol command initiated from the server  26  or router  12 . However, if the network command fails, the compressed core file  61  in local flash memory  22  can be accessed through the console  28  or other devices coupled to auxiliary port  30 . 
     Having described and illustrated the principles of the invention in a preferred embodiment thereof, it should be apparent that the invention can be modified in arrangement and detail without departing from such principles. I claim all modifications and variation coming within the spirit and scope of the following claims.

Technology Category: 4