Automatic correction of data polarity on a differential serial bus
Methods and structure described herein provide for detecting data inversions between electronic devices in communication with one another and automatically correcting those that inversions. An electronic device may be configured with a receiver that is configured for receiving differential serial data from a transmitter of another electronic device. The differential serial data is formatted according to a particular communication protocol associated with the electronic devices. The receiver detects an invalid sequence in the received differential serial data, such as an inverted SAS primitive, and automatically change the receive logic of the receiver such that subsequent received differential serial data is in the proper polarity. The transmitting device does not require notification of the change in receive logic.
1. A method, comprising:
receiving differential serial data;
detecting a polarity inversion in the received differential serial data by determining an invalid sequence in the received differential serial data; and
changing polarity of subsequent received differential serial data in response to detecting the polarity inversion.
2. The method of claim 1 , further comprising
decoding the received differential serial data from a first data format to a second data format.
3. The method of claim 2 , wherein
the first data format is a ten bit data format and the second data format is an eight bit data format.
4. The method of claim 1 , wherein
the received differential serial data is formatted according to a communication protocol.
5. The method of claim 4 , wherein
the communication protocol is a Serial Attached Small Computer System Interface (SAS) protocol and wherein the invalid sequence is an inverted SAS primitive.
6. The method of claim 4 , wherein
the communication protocol is devoid of a polarity checking sequence.
7. The method of claim 4 , wherein
said detecting a polarity inversion comprises comparing a received sequence to a valid communication protocol sequence.
8. The method of claim 1 , wherein
said changing polarity comprises automatically changing polarity of the subsequent received differential serial data in response to detecting the polarity inversion, wherein automatically changing the polarity is performed independent of an external device used to transmit the differential serial data.
9. The method of claim 1 , further including
changing polarity of the invalid sequence in response to detecting the polarity inversion.
10. A data receiver, comprising:
a data interface adapted to receive differential serial data;
a detector communicatively coupled to the data interface and adapted to detect a data inversion in the received differential serial data, wherein the detector detects the data inversion by determining an invalid sequence in the received differential serial data and wherein the detector is further adapted to generate a control signal used to change polarity of subsequent differential serial data; and
data inversion logic adapted to receive the control signal and change the polarity of the received differential serial data.
11. The data receiver of claim 10 , wherein
the invalid sequence is an inverted Serial Attached Small Computer System Interface (SAS) primitive.
12. The data receiver of claim 11 , wherein
the inverted SAS primitive is an ALIGN(0) primitive.
13. The data receiver of claim 10 , further comprising
a decoder communicatively coupled to the data interface and adapted to decode the received differential serial data from a first data format to a second data format.
14. The data receiver of claim 13 , wherein
the received differential serial data comprises an 8b/10b encoding, wherein the first data format is a 10 bit format and the second data format is an 8 bit data format.
15. A computer readable media for detecting a polarity inversion in received differential serial data and automatically correcting the polarity inversion, the computer readable media including software instructions that, when executed by a computer processor, direct the computer processor to:
receive differential serial data;
detect a polarity inversion in the received differential serial data by determining an invalid sequence in the received differential serial data; and
change polarity of subsequent received differential serial data in response to detecting the polarity inversion.
16. The computer readable media of claim 15 , further comprising
instructions that, when executed by a computer processor, direct the computer processor to decode the received differential serial data from a first data format to a second data format, wherein the first data format is a ten bit data format and the second data format is an eight bit data format.
17. The computer readable media of claim 15 , wherein
the received differential serial data is formatted according to a communication protocol that is devoid of a polarity checking sequence and wherein detection of the polarity inversion comprises comparing a received sequence to a valid communication protocol sequence.
18. The computer readable media of claim 17 , wherein
the communication protocol is a Serial Attached Small Computer System Interface (SAS) protocol and wherein the invalid sequence is an inverted SAS primitive.
19. The computer readable media of claim 15 , wherein
said changing polarity comprises automatically changing polarity of the subsequent received differential serial data in response to detecting the polarity inversion, wherein automatically changing the polarity is performed independent of an external device used to transmit the differential serial data.