System for transferring digital data between a host device and a recording medium

• US 4,672,613 A
• Filed: 11/01/1985
• Issued: 06/09/1987
• Est. Priority Date: 11/01/1985
• Status: Expired due to Term

• Current Assignee: Seagate Removable Storage Solutions LLC (Chi Ko Investment Co., Ltd.)
• Original Assignee: Cipher Data Products, Inc. (Whitehouse Group Ltd.)
• Inventors: Clark, William S. Jr., Foxworthy, Neal E., Gabbay, Robert J., Schossow, Stephen R.
• Primary Examiner(s): Atkinson, Charles E.
• Application Number:
  US06/794,070
• Time in Patent Office: 585 Days
• Field of Search: 371/38, 364/200, 364/900
• US Class Current: 714/763
• CPC Class Codes: G06F 11/10 Adding special bits or symbols to the coded information, e.g. parity check, casting out 9's or 11's
• CPC Class Codes: G06F 13/28 using burst mode transfer, e.g. direct memory access DMA, cycle steal G06F13/32 takes precedence
• CPC Class Codes: G06F 3/0601 Interfaces specially adapted for storage systems
• CPC Class Codes: G06F 3/0656 Data buffering arrangements

Abstract

In a system for transferring data between a host device and a target recording medium, a buffer interface control unit includes a host direct memory access (DMA) unit for transferring data from the host unit to a buffer memory. The host DMA unit accesses a first set of prescribed noncontinuous buffer memory storage locations to store the data transferred from the host unit in a predetermined buffer format that includes additional sets of prescribed storage locations interspersed with the first set of data storage locations for the storage of error code characters pertaining to the data. The host DMA unit also transfers error correction code characters pertaining to the data to one of the additional sets of prescribed storage locations. The buffer interface control unit further includes a target DMA unit for transferring data from the buffer memory to a write interface unit. The target DMA unit accesses the buffer memory storage locations in a predetermined noncontinuous sequence in order to retrieve the data from the buffer memory in a format that includes open time slots interspersed with time slots occupied by the retrieved data for the insertion of error detection code characters pertaining to the data retrieved from the buffer memory.

Claims

1. A system for transferring digital data between a host device and a target recording medium, comprising

a buffer memory having a matrix of storage locations for storing digital data;

a write interface unit for transferring data to a target recording medium for recording;

a read interface unit for reading and processing data from a target recording medium; and

a buffer interface control unit for transferring data from the host device to the buffer memory and from the buffer memory to the write interface unit during a writing mode of operation, and for transferring data from the read interface unit to the buffer memory and from the buffer memory to the host device during a retrieval mode of operation, wherein the buffer interface control unit comprises

means for generating error correction code characters pertaining to said data as said data is being transferred to the buffer memory; and

a host direct memory access (DMA) unit for transferring the data from the host unit to the buffer memory, and for transferring the generated error correction code characters to the buffer memory; and

a target DMA unit for transferring the data and the error correction codes from the buffer memory to the write interface unit;

wherein the host DMA unit includes means for accessing a first set of prescribed noncontinuous buffer memory storage locations during the writing mode of operation in order to store the data transferred from the host unit in the buffer memory in a predetermined buffer format that includes additional sets of prescribed storage locations interspersed with the first set of data storage locations for the storage of error code characters pertaining to said data, and means for accessing one of the additional sets of prescribed storage locations during the writing mode of operation in order to store the error correction code characters so that they are interspersed with the data in the predetermined buffer format; and

wherein the target DMA unit includes means for accessing the first set and the one additional set of prescribed buffer memory storage locations in a predetermined noncontinuous sequence in order to retrieve the data and the error correction code characters from the buffer memory in a format that includes open time slots interspersed with time slots occupied by the retrieved data and error correction code characters for the insertion of error detection code characters pertaining to the retrieved data and error correction code characters.

2. A system according to claim 1,

wherein the buffer interface control unit further comprises means for generating error control information pertaining to said data as said data is being transferred to the buffer memory;

and

wherein the host direct memory access (DMA) unit further comprises means for transferring the generated control information to the buffer memory, said transferring means including means for accessing another set of prescribed storage locations in the buffer memory during the writing mode of operation in order to store the control information with the data in the predetermined buffer format.

3. A system according to claim 1,

wherein the target DMA unit includes means for transferring the data from the buffer memory to the write interface unit in an order different than the order in which the data was transferred to the buffer memory by the host DMA unit.

4. A system according to claim 3,

wherein the buffer memory includes a storage matrix comprising columns and rows of storage locations;

wherein the host DMA unit includes means for accessing the storage locations of the buffer memory in a column-by-column sequence in order to store the data transferred from the host unit; and

wherein the target DMA unit includes means for accessing the storage locations of the buffer memory in a row-by-row sequence in order to retrieve the data from the buffer memory for transfer to the write interface unit.

5. A system according to claim 1,

wherein the write interface unit comprises means for generating error detection code characters pertaining to said retrieved data and error correction code characters, means for inserting said generated error detection code characters in said open time slots, and and means for processing the interspersed data and error code characters for transfer to the target recording medium in a predetermined data recording format.

6. A system according to claim 5,

wherein the target DMA unit includes means for transferring the data read and error correction code characters by the read interface unit to the buffer memory for storage in the same buffer format during the retrieval mode of operation as the buffer format said data and error correction code characters were retrieved from by the target DMA unit during the writing mode of operation, and means for transferring error detection code characters read by the read interface unit during the retrieval mode of operation to the buffer memory for storage in another of the additional sets of prescribed storage locations within said buffer format.

7. A system according to claim 5,

wherein said predetermined data recording format includes sectors of data separated by synchronization code characters that indicate respectively adjacent data sectors;

wherein the read interface unit comprises means for reading whatever is being recorded on the target recording medium while recording is taking place, means for processing error detection code characters read from the recording medium to detect errors in recording, and means responsive to the read synchronization code characters for indicating sectors in which a recording error is detected;

wherein the target DMA unit comprises means that respond to said sector-error indication during the writing mode of operation by again transferring to the write interface unit from the buffer memory the sector of data for which the error was indicated; and

wherein the buffer interface control unit further comprises means that respond to said sector-error indication by accessing said buffer memory and inserting control information in said sector of again-transferred data indicating that said sector is being rerecorded on said target recording medium.

8. A system according to claim 7,

wherein the target DMA unit includes means for transferring the data read by the read interface unit to the buffer memory for storage in the same buffer format during the retrieval mode of operation as the buffer format said data was retrieved from by the target DMA unit during the writing mode of operation, and means for accessing the corresponding first set of prescribed buffer memory storage locations in a predetermined sequence that is dependent upon said rerecorded-sector indication to ultimately store the sector of rerecorded data instead of the erroneously recorded sector of data in the storage locations of said buffer format corresponding to the storage locations that said rerecorded data was retrieved from during the writing mode of operation.

9. A system according to claim 5,

wherein said predetermined data recording format includes sectors of data separated by synchronization code characters that indicate respectively adjacent data sectors;

wherein the read interface unit comprises means for processing error detection code characters read from the recording medium during the retrieval mode to detect errors in recording, and means responsive to the read synchronization code characters for indicating sectors in which a recording error is detected;

wherein the target DMA unit includes means for transferring data read by the read interface unit to the buffer memory for storage in the same buffer format during the retrieval mode of operation as the buffer format said data was retrieved from by the target DMA unit during the writing mode of operation; and

wherein the buffer interface control unit further comprises means that respond to said sector-error indication during the retrieval mode of operation by retrieving from the buffer memory each sector of data for which said sector-error was indicated, by processing said retrieved data sector to correct said error, and by storing said corrected data sector in the buffer memory in the same storage locations that the error-indicated data sector was retrieved from.

10. A system according to claim 5,

wherein said predetermined data recording format includes sectors of data separated by synchronization code characters and containing resynchronization code characters at different positions within each sector;

wherein the buffer interface control unit further comprises means for monitoring said synchronization code character detection indications during the retrieval mode of operation, and means for responding to said monitoring by providing a synchronization indication for those sectors for which the synchronization code characters are detected and by providing a loss of synchronization indication when synchronization code characters are not detected when they should be detected; and

11. A system according to claim 1, wherein the target DMA unit includes means for transferring data read by the read interface unit to the buffer memory for storage in the same format during the retrieval mode of operation as the format said data was transferred from by the target DMA unit during the writing mode of operation.

12. A system according to claim 11,

wherein the buffer interface control unit further comprises means for selectively generating control information indicating that data is to be read from the target recording medium during the retrieval mode of operation in the reverse direction in relation to a forward direction in which the data was recorded during the writing mode of operation;

wherein the read interface unit includes means that respond to said reverse-direction control information by reading the recording medium in said reverse direction during the retrieval mode of operation;

wherein the target DMA unit includes means for accessing the corresponding first set of prescribed buffer memory storage locations in a predetermined sequence that is dependent upon said reverse-direction control information in order to store the data in the same format that said data would have been stored in if the data had been read from the recording medium in the forward direction; and

wherein the host DMA unit includes means for accessing the corresponding first set of prescribed buffer memory storage locations in a predetermined sequence that is dependent upon said reverse-direction control information in order to transfer data from the buffer memory for transfer to said host device during the retrieval mode of operation in the reverse order from the order that said data was transferred by the host DMA unit to the buffer memory during the writing mode of operation.

13. A system according to claim 1, wherein the host DMA unit includes means for transferring data from the buffer memory for transfer to host unit during the retrieval mode of operation in the same format as said data was transferred by the host DMA device to the buffer memory during the writing mode of operation.

14. A system for transferring digital data between a host device and a target recording medium, comprising

a buffer memory having a matrix of storage locations for storing digital data;

a write interface unit for transferring data to a target recording medium for recording;

a read interface unit for reading and processing data from a target recording medium; and

a buffer interface control unit for transferring data between the host device and the buffer memory, for transferring data from the buffer memory to the write interface unit during a writing mode of operation, and for transferring data from the read interface unit to the buffer memory during a retrieval mode of operation, wherein the buffer interface control unit comprises

a target direct memory access (DMA) unit for transferring the data from the buffer memory to the write interface unit, wherein the target DMA unit includes means for accessing a first set of prescribed buffer memory storage locations in a predetermined noncontinuous sequence in order to retrieve the data from the buffer memory in a format that includes open time slots interspersed with time slots occupied by the retrieved data for the insertion of code characters pertaining to said data retrieved from the buffer memory.

15. A system according to claim 14,

wherein the write interface unit comprises means for generating error code characters pertaining to said retrieved data, means for inserting said generated error code characters in said open time slots interspersed with said retrieved data, and means for processing the interspersed data and error code characters for transfer to the target recording medium in a predetermined data recording format;

and

wherein the target DMA unit includes means for transferring data read by the read interface unit to the buffer memory for storage in the same buffer format during the retrieval mode of operation as the buffer format said data was retrieved from by the target DMA unit during the writing mode of operation, and means for transferring error code characters read by the read interface unit during the retrieval mode of operation to the buffer memory for storage in predetermined storage locations within a corresponding second set of prescribed storage locations within said buffer format.

16. A system according to claim 14,

wherein the write interface unit comprises means for generating error code characters pertaining to said retrieved data, means for inserting said generated error code characters in said open time slots interspersed with said retrieved data, and means for processing the interspersed data and error code characters for transfer to the target recording medium in a predetermined data recording format;

wherein said predetermined data recording format includes sectors of data separated by synchronization code characters and containing error code characters pertaining to the data in such sector;

wherein the read interface unit comprises means for reading whatever is being recorded on the target recording medium while recording is taking place, means for processing error code characters read from the recording medium to detect errors in recording, and means for indicating sectors in which a recording error is detected;

wherein the target DMA unit comprises means that respond to said sector-error indication during the writing mode of operation by again transferring to the write interface unit from the buffer memory the sector of data for which the error was indicated; and

wherein the buffer interface control unit further comprises means that respond to said sector-error indication by accessing the buffer memory and inserting control information in said sector of again-transferred data indicating that said sector is being rerecorded on said target recording medium.

17. A system according to claim 16,

wherein the target DMA unit includes means for transferring data read by the read interface unit to the buffer memory for storage in the same format during the retrieval mode of operation as the format said data was retrieved from by the target DMA unit during the writing mode of operation, and means for accessing the corresponding first set of prescribed buffer memory storage locations in a second predetermined sequence that is dependent upon said rerecorded-sector indication to ultimately store the sector of rerecorded data instead of the erroneously recorded sector of data in the storage locations of said format corresponding to the storage locations that said rerecorded data was retrieved from during the writing mode of operation.

18. A system according to claim 14,

wherein the write interface unit comprises means for generating error code characters pertaining to said retrieved data, means for inserting said generated error code characters in said open time slots interspersed with said retrieved data, and means for processing the interspersed data and error code characters for transfer to the target recording medium in a predetermined data recording format;

wherein the read interface unit comprises means for processing the error code characters read from the recording medium during the retrieval mode of operation to detect errors in recording, and means for indicating sectors in which a recording error is detected;

wherein the target DMA unit includes means for transferring data read by the read interface unit to the buffer memory for storage in the same format during the retrieval mode of operation as the format said data was retrieved from by the target DMA unit during the writing mode of operation; and

wherein the buffer interface control unit further comprises means that respond to said sector-error indication during the retrieval mode of operation by retrieving from the buffer memory each sector of data for which said sector-error was indicated, by processing said retrieved data sector to correct said error, and by storing said corrected data sector in the buffer memory in the same storage locations that the error-indicated data sector was retrieved from.

19. A system according to claim 15,

wherein the write interface unit comprises means for generating error code characters pertaining to said retrieved data, means for inserting said generated error code characters in said open time slots interspersed with said retrieved data, and means for processing the interspersed data and error code characters for transfer to the target recording medium in a predetermined data recording format;

wherein said predetermined data recording format includes sectors of data separated by synchronization code characters and containing resynchronization code characters at different positions within each sector;

wherein the read interface unit comprises means for detecting synchronization code characters and resynchronization code characters read from the recording medium during the retrieval mode of operation, and means for indicating whether the synchronization code characters and the resynchronization code characters are detected;

wherein the buffer interface control unit further comprises means for monitoring said synchronization code character detection indications during the retrieval mode of operation, and means for responding to said monitoring by providing a synchronization indication for those sectors for which the synchronization code characters are detected and by providing a loss of synchronization indication when synchronization code characters are not detected when they should be detected; and

wherein the target DMA unit includes means for transferring data read by the read interface unit to the buffer memory for storage in the same buffer format during the retrieval mode of operation as the buffer format said data was transferred from by the target DMA unit during the writing mode of operation when said synchronization indication is provided, means for responding to said loss of synchronization indication by interrupting all transfer from the read interface unit to the buffer memory, means for responding to an indication that a said resynchronization code character was not detected when it was supposed to be detected by interrupting all transfer from the read interface unit to the buffer memory, and means for responding to a subsequent indication that a resynchronization code character was detected when it was supposed to be detected by resuming transfer of the remainder of the data in the sector to the storage locations in the buffer format corresponding to the storage locations that said data was retrieved from during the writing mode of operation.

20. A system according to claim 14, wherein the target DMA unit includes means for transferring data read by the read interface unit to the buffer memory for storage in the same format during the retrieval mode of operation as the format said data was transferred from by the target DMA unit during the writing mode of operation.

21. A system according to claim 20,

wherein the buffer interface control unit further comprises means for selectively generating control information indicating that data is to be read from the target recording medium during the retrieval mode of operation in the reverse direction in relation to a forward direction in which the data was recorded during the writing mode of operation;

wherein the read interface unit includes means that respond to said reverse-direction control information by reading the recording medium in said reverse direction during the retrieval mode of operation; and

wherein the target DMA unit includes means for accessing the corresponding first set of prescribed buffer memory storage locations in a predetermined sequence that is dependent upon said reverse-direction control information in order to store the data in the same format that said data would have been stored in if the data had been read from the recording medium in the forward direction.