Abstract: Method and circuitry for de-skewing data in data communication networks such as a SONET. The data is sent from a system chip to a framer chip where the data is de-skewed. To detect data skew, the system chip sends a training sequence to the framer chip. The information bits sent to the framer chip are searched in order to detect the training sequence. The training sequences contain clear transition patterns at which all 16 bits of the transmit data and the TCTL signal line are inverted. If any bit does not invert, this bit must be a skewed bit. Based on the data one clock cycle before and one clock cycle after this transition, the skewed bit can be corrected back. After the data skew is detected, a multiplexing logic circuitry is used to correct the skew based on one clock cycle either before or after the transition. The multiplexing logic circuitry includes at least three registers coupled to the inputs of the multiplexing logic circuitry.

Abstract: A cyclic redundancy check (CRC) generator, in accordance with a specific embodiment of the present invention, generates a 32-bit CRC for each packet whose data bytes are carried over a 128-bit bus by first dividing the data bytes by a 123nd degree generator polynomial and subsequently dividing the remainder of the first division by a 32nd degree generator polynomial. Data bytes of a new packet are divided by a different dividing logic than those of a current packet. The remainder of division performed on the bytes of a new packet are supplied to the dividing logic adapted to divide the bytes of a current packet. The division by the 123nd degree generator polynomial is performed on a per byte basis, with the remainder of the division of the (i+1)th byte being used in the division of the ith byte.

Abstract: A cyclic redundancy check (CRC) generator, in accordance with a specific embodiment of the present invention, generates a 32-bit CRC for each packet whose data bytes are carried over a 128-bit bus by first dividing the data bytes by a 123nd degree generator polynomial and subsequently dividing the remainder of the first division by a 32nd degree generator polynomial. Data bytes of a new packet are divided by a different dividing logic than those of a current packet. The remainder of division performed on the bytes of a new packet are supplied to the dividing logic adapted to divide the bytes of a current packet. The division by the 123nd degree generator polynomial is performed on a per byte basis, with the remainder of the division of the (i+1)th byte being used in the division of the ith byte.

Abstract: Method and circuitry for de-skewing data in data communication networks such as a SONET. The data is sent from a system chip to a framer chip where the data is de-skewed. To detect data skew, the system chip sends a training sequence to the framer chip. The information bits sent to the framer chip are searched in order to detect the training sequence. The training sequences contain clear transition patterns at which all 16 bits of the transmit data and the TCTL signal line are inverted. If any bit does not invert, this bit must be a skewed bit. Based on the data one clock cycle before and one clock cycle after this transition, the skewed bit can be corrected back. After the data skew is detected, a multiplexing logic circuitry is used to correct the skew based on one clock cycle either before or after the transition. The multiplexing logic circuitry includes at least three registers coupled to the inputs of the multiplexing logic circuitry.

Abstract: Method and apparatus for processing data packets within a communication system such as a synchronous optical network (SONET) detect an invalid byte and drop and shift bytes of data to address an invalid byte. A method according to one embodiment of the present invention, includes receiving a first data packet in the communication system. Thereafter, it is determined whether this packet ends with both a valid byte and an invalid byte of data. If both the valid and invalid bytes are present, the invalid byte is dropped and a valid byte from a succeeding data packet is concatenated with the valid byte of the first data packet, and byte shifting occurs in the succeeding data packet. Byte shifting continues until a second packet ending with an invalid byte is encountered. Skipping a clock cycle at the end of the second packet with the invalid byte results in packets with only valid data.

Abstract: A cyclic redundancy check (CRC) generator, in accordance with a specific embodiment of the present invention, generates a 32-bit CRC for each packet whose data bytes are carried over a 128-bit bus by first dividing the data bytes by a 123nd degree generator polynomial and subsequently dividing the remainder of the first division by a 32nd degree generator polynomial. Data bytes of a new packet are divided by a different dividing logic than those of a current packet. The remainder of division performed on the bytes of a new packet are supplied to the dividing logic adapted to divide the bytes of a current packet. The division by the 123nd degree generator polynomial is performed on a per byte basis, with the remainder of the division of the (i+1)th byte being used in the division of the ith byte.

Abstract: Method and apparatus for processing data packets within a communication system such as a synchronous optical network (SONET) detect an invalid byte and drop and shift bytes of data to address an invalid byte. A method according to one embodiment of the present invention, includes receiving a first data packet in the communication system. Thereafter, it is determined whether this packet ends with both a valid byte and an invalid byte of data. If both the valid and invalid bytes are present, the invalid byte is dropped and a valid byte from a succeeding data packet is concatenated with the valid byte of the first data packet, and byte shifting occurs in the succeeding data packet. Byte shifting continues until a second packet ending with an invalid byte is encountered. Skipping a clock cycle at the end of the second packet with the invalid byte results in packets with only valid data.

Abstract: Method and circuitry for de-skewing data in data communication networks such as a SONET. The data is sent from a system chip to a framer chip where the data is de-skewed. To detect data skew, the system chip sends a training sequence to the framer chip. The information bits sent to the framer chip are searched in order to detect the training sequence. The training sequences contain clear transition patterns at which all 16 bits of the transmit data and the TCTL signal line are inverted. If any bit does not invert, this bit must be a skewed bit. Based on the data one clock cycle before and one clock cycle after this transition, the skewed bit can be corrected back. After the data skew is detected, a multiplexing logic circuitry is used to correct the skew based on one clock cycle either before or after the transition. The multiplexing logic circuitry includes at least three registers coupled to the inputs of the multiplexing logic circuitry.

Abstract: A circuit and method for switching between different frequency clock domains that are out of phase. The circuit has a select input for selecting which frequency domain is to be output, a first circuit associated with the first clock domain, and a second circuit associated with the second clock domain. The first and second circuits are responsive to the select input and work together to disengage the first clock before the second clock is engaged.

Abstract: Method and apparatus for processing data packets within a communication system such as a synchronous optical network (SONET) detect an invalid byte and drop and shift bytes of data to address an invalid byte. A method according to one embodiment of the present invention, includes receiving a first data packet in the communication system. Thereafter, it is determined whether this packet ends with both a valid byte and an invalid byte of data. If both the valid and invalid bytes are present, the invalid byte is dropped and a valid byte from a succeeding data packet is concatenated with the valid byte of the first data packet, and byte shifting occurs in the succeeding data packet. Byte shifting continues until a second packet ending with an invalid byte is encountered. Skipping a clock cycle at the end of the second packet with the invalid byte results in packets with only valid data.