Browse Prior Art Database

Protection Against Shift Faults in Disk File Interface

IP.com Disclosure Number: IPCOM000038810D
Original Publication Date: 1987-Mar-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 47K

Publishing Venue

IBM

Related People

Crossland, P: AUTHOR

Abstract

A disk file interface includes a serializer/deserializer (SERDES). When an input byte is fed to the SERDES, its parity bit is stored. A parity generator operates on the input data, and the parity generated is checked against the stored parity bit. In addition, an echo check comparator detects inequalities between a byte without a parity bit sent to the file and the same byte received from the file. The figure shows a simplified version of a disk file Serial Control Interface. Parallel Serial Control data is transmitted by serializing the contents of an 8-bit register (not shown) which has been previously loaded by a microprocessor. A Parity Bit is not transmitted to the disk file in order to reduce transmission time.

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Protection Against Shift Faults in Disk File Interface

A disk file interface includes a serializer/deserializer (SERDES). When an input byte is fed to the SERDES, its parity bit is stored. A parity generator operates on the input data, and the parity generated is checked against the stored parity bit. In addition, an echo check comparator detects inequalities between a byte without a parity bit sent to the file and the same byte received from the file. The figure shows a simplified version of a disk file Serial Control Interface. Parallel Serial Control data is transmitted by serializing the contents of an 8-bit register (not shown) which has been previously loaded by a microprocessor. A Parity Bit is not transmitted to the disk file in order to reduce transmission time.

Errors caused by Line Drivers/Receivers or by cabling and connector faults are detected by an 'Echo-Checking' method, whereby the disk file echoes back the Serial Data Out (SDO) content along the Serial Data In line. Although the Serial Data In (SDI) is shifted back into the SERDES, the 'Echo-Check' comparison occurs before the bit is clocked into the SERDES, in order to reduce the total time needed to transmit a byte. Serial Sense data is received in a similar way, with the device which sends out the Sense Data on the SDI, receiving echoed data back on the SDO. In the figure: THE PARITY LATCH is loaded when the SERDES is loaded with a Command or Parameter Byte before a transfer to the File THE PARITY COMPARATOR detects Parity Errors in the Data loaded, before a transfer to the disk file. THE ECHO CHECK COMPARATOR detects inequalities between the value of SDO and the SDI returned from the file, during the transfer of a Command or Parameter Byte to the file Problems with Undetected Errors The system described above is an LSSD (level sensitive scan design) design. This means that the latches used in the SERDES comprise L1/L2 latch pairs, and hence the SERDES constitutes such a significant amount of logic, that the possibility of an error occurring in the shifting portion of the SERDES logic is sufficient that it must be protected against. The 'Echo-Checking' mechanism, described above, will not detect errors in the SERDES serialization/deserialization logic. Thus, any error in the SERDES which would cause one of the SERDES latches to malfunction, and thus produce an erroneous value on the SDO line, would...