Fiber channel CRC for internal error checking on a switching platform

• US 6,647,528 B1
• Filed: 11/02/2000
• Issued: 11/11/2003
• Est. Priority Date: 11/02/2000
• Status: Expired due to Fees

• Current Assignee: McData Services Corp. (Broadcom, Inc.)
• Original Assignee: Computer Network Technology Corp. (Broadcom, Inc.)
• Inventors: Vogel, Mark J., Ketchum, Bret, Flattum, Steve A., Collette, William C.
• Primary Examiner(s): Chung, Phung M.
• Application Number:
  US09/705,012
• Time in Patent Office: 1,104 Days
• Field of Search: 714/758, 714/819, 714/807
• US Class Current: 714/758
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• CPC Class Codes: H04L 1/0061 Error detection codes
• CPC Class Codes: H04L 1/0072 Error control for data other than payload data, e.g. control data

Abstract

A method and apparatus is presented for performing a sequence-level CRC calculation on fiber channel communications within a switching platform domain. Specifically, the disclosed invention utilizes a CRC generator to monitor data communication between an external interface and a fiber channel controller. The CRC generator searches the data communication for frames that contain the type of data for which a sequence-level CRC is desired, such as for a sequence containing SCSI data. When found, the CRC generator performs an 8B/10B decode, strips off any fill bytes, and performs a CRC calculation on the data payload. If the found frame is the first frame in the sequence, the CRC is done starting with a reset value. If the frame is not the first, an intermediate value containing the previous CRC calculation results for this sequence is retrieved and used to perform the CRC calculations. Upon completion of the calculation for the frame, a determination is made whether the sequence is complete. If so, the calculated value is the sequence-level CRC. If not, the calculated value is stored in memory for use with the next frame in that sequence. With inbound data, the calculated sequence-level CRC is appended to the end of the data comprising that sequence. With outbound data, the calculated value is compared with the appended, expected value, and a CRC error is generated if the values do not match. The sequence-level CRC value appended to the sequence data is typically removed before the data exits the switching platform domain.

Claims

1. A fibre channel interface to a fibre channel communications line comprising:

a) an external interface connected to the communications line so as to receive and transmit fibre channel frames having headers and data payloads over the communications line;

b) a fibre channel controller receiving frames from the external interface; and

c) a CRC module connected so as to monitor data flowing between the external interface and the fibre channel controller;

the CRC module having

i) a first CRC generator that generates a CRC value based on a starting value and data to be analyzed

ii) a first frame header processor with circuitry to analyze headers and transmit data payloads to the CRC generator as data to be analyzed; and

iii) a first memory in communication with the first CRC generator that stores intermediate CRC values for a sequence for later use by the first CRC generator as the starting value when analyzing a next frame in the sequence.

2. The fibre channel interface of claim 1, further comprising a SERDES to convert parallel data used by the fibre channel controller to serial data used by the external interface.

3. The fibre channel interface of claim 2, wherein the queue index is the same as an exchange ID that is determined by the fibre channel interface.

4. The fibre channel interface of claim 2, further comprising a queue in the first memory for storage and retrieval of the data payload data used to calculate the CRC value.

5. The fibre channel interface of claim 1, further comprising a queue in the first memory for storage of and retrieval of intermediate CRC values according to a queue index.

6. The fibre channel interface of claim 1, wherein the first frame header processor passes less than all of the data payloads monitored by the CRC module based upon the analysis of the headers.

7. The fibre channel interface of claim 6, wherein the first frame header processor passes only data payloads of frames containing SCSI data.

8. The fibre channel interface of claim 1, wherein the fibre channel controller has a memory interface in communication with the first memory of the CRC module, and further wherein the fibre channel controller has a bus interface for allowing accessing to the first memory of the CRC module over the bus interface.

9. The fibre channel interface of claim 1, wherein the CRC module further comprises:

iv) a second CRC generator that generates a CRC value based on a starting value and data to be analyzed; and

v) a second frame header processor with circuitry to analyze headers and transmit data payloads to the CRC generator as data to be analyzed;

wherein the first CRC generator and the first frame header processor both process incoming data over the external interface while the second CRC generator and the second frame header processor both process outgoing data over the external interface.

10. The fibre channel interface of claim 9, wherein the first memory is in communication with the second CRC generator to store intermediate CRC values for later use by the second CRC generator as the starting value when analyzing a next frame in the sequence.

11. The fibre channel interface of claim 9, further comprising a second memory in communication with the second CRC generator, the second memory storing intermediate CRC values for later use by the second CRC generator as the starting value when analyzing a next frame in the sequence.

12. In a switching platform having

a) a communications bus;

b) a system buffer connected to the communications bus;

c) a first interface connected the communications bus;

d) a fibre channel interface connected to a fibre channel communications line and the communications bus; and

e) a processor connected to the communications bus, the processor translating data between the first interface and the fibre channel interface using the system buffer as temporary storage;

an improved fibre channel interface wherein the fibre channel interface comprises;

i) a CRC generator that generates a CRC value based on a starting value and data to be analyzed;

ii) a frame header processor that monitors communications between the communications bus and the fibre channel communications line at the level of a fibre channel frame, the frame header processor having circuitry to analyze a header within the frame to determine the type of data within the frame and a sequence to which the frame belongs, the frame header processor being in communication with the CRC generator so as to transmit a data payload of the frame to the CRC generator as data to be analyzed; and

iii) memory in communication with the CRC generator that stores intermediate CRC values for later use by CRC generator as the starting value when analyzing a next frame in the sequence.

13. The switching platform of claim 12, wherein the frame header processor selectively transmits the data payload of the frame to the CRC generator based on the header of the frame.

14. The switching platform of claim 12, wherein the memory stores a final sequence-level CRC calculation after all frames in a sequence have been analyzed by the CRC generator.

15. The switching platform of claim 14, wherein data being transmitted from fibre channel interface to the first interface is altered by the processor by appending the final sequence-level CRC calculation stored in memory to the data of the sequence.

16. The switching platform of claim 15, wherein the data being transmitted from the first interface to the fibre channel interface contains an expected, sequence-level CRC value appended to the data, wherein the CPU strips the expected CRC value before submitting the data to the fibre channel interface.

17. The switching platform of claim 16, wherein the CPU compares the stripped-off expected CRC value with the CRC value calculated for the data by the CRC generator.

18. The switching platform of claim 16, wherein the fibre channel interface further comprises CRC compare circuitry that compares the final sequence-level CRC calculation to the stripped-off expected CRC value.

19. The switching platform of claim 18, wherein the CPU stores the stripped-off expected CRC value in the memory.

20. The switching platform of claim 12, wherein the first interface is a wide area network interface.

21. The switching platform of claim 12, wherein the first interface is a channel interface.

22. A method for calculating a sequence-level CRC calculation for fibre channel data comprising:

a) performing a CRC calculation on a data payload of a first frame to create an intermediate CRC calculation;

b) storing the intermediate CRC calculation so as to associate the intermediate CRC calculation with the fibre channel sequence of which the first frame is a member;

c) retrieving the intermediate CRC calculation when an additional frame is received that belongs to the same fibre channel sequence as the first frame;

d) using the intermediate CRC calculation as the starting point to perform a CRC calculation on the data payload of the additional frame to create a new intermediate CRC calculation;

e) storing the new intermediate CRC calculation if the additional frame is not the last frame of the sequence; and

f) performing steps c, d, and e until the last frame of the sequence has been received and used to perform the CRC calculation.

23. The method of claim 22, further comprising the step of storing of the final CRC calculation in memory as the sequence-level CRC value.

24. The method of claim 23, further comprising the step of appending the sequence-level CRC value to the end of the data contained in the sequence.

25. The method of claim 24, further comprising the step of stripping off any sequence-level CRC value from data payloads before performing any CRC calculations.

26. The method of claim 25, further comprising the step of comparing the final CRC calculation with the value of a sequence-level CRC value attached to the end of the data payload of the last frame of the sequence.

27. The method of claim 22, further comprising the step of stripping off fill bits before performing any CRC calculations.