SERIAL LINK BUFFER FILL-LEVEL COMPENSATION USING MULTI-PURPOSE START OF PROTOCOL DATA UNIT TIMING CHARACTERS

• US 20090276550A1
• Filed: 04/30/2008
• Published: 11/05/2009
• Est. Priority Date: 04/30/2008
• Status: Active Grant

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Alcatel-Lucent SA (Nokia Corporation)
• Inventors: Megarity, Mark
• Granted Patent: US 9,047,421 B2
• Time in Patent Office: Days
• US Class Current: 710/53
• CPC Class Codes: G06F 13/4286 using a handshaking protocol, e.g. RS232C link

Abstract

Embodiments of the invention provide improved timing compensation for a bidirectional serial link in order to relax accuracy requirements of clock sources used for the link. Fill levels of receiver buffers at either ends of the link are used to determine a particular type of start of PDU (SOP) character sequence to use when forming a PDU for transmission over the link. When a given type of SOP character sequence is present in a PDU received at one end of the link, a next PDU to be transmitted from the same end of the link is delayed by a predetermined amount of time to allow the receiver buffer at the other end of the link to decrease its fill level before receiving the next PDU.

Claims

1. A circuit card for communicating protocol data units PDUs over a bidirectional serial link that includes a first unidirectional serial link for communicating PDUs in one direction and a second unidirectional serial link for communicating PDUs in an opposite direction, the circuit card comprising:

a transmitter module for transmitting PDUs over the first unidirectional serial link;

a receiver module for receiving PDUs from the second unidirectional serial link; and

a control link coupling the receiver module to the transmitter module for conveying control indications from the receiver module to the transmitter module.

2. The circuit card of claim 1, wherein:

the receiver module includes a receiver buffer for storing PDUs received from the second unidirectional serial link and is operable to determine and send a particular control indication to the transmitter module, the determination depending upon a relationship between a fill level of the receiver buffer and a threshold; and

the transmitter module is operable to determine and use a particular start of PDU SOP character sequence to form a next PDU to be transmitted over the first unidirectional serial link, the determination depending upon the particular control indication received from the receiver module.

3. The circuit card of claim 2, wherein:

the receiver module is further operable to send a first control indication as the particular control indication to the transmitter module responsive to the fill level being below the threshold; and

the transmitter module is further operable use a first SOP character sequence as the particular SOP character sequence responsive to receiving the first control indication as the particular control indication.

4. The circuit card of claim 3, wherein:

the receiver module is further operable to send a second control indication as the particular control indication to the transmitter module responsive to the fill level being above the threshold; and

the transmitter module is further operable use a second SOP character sequence as the particular SOP character sequence responsive to receiving the second control indication as the particular control indication.

5. The circuit card of claim 1, wherein the receiver module is operable to determine and send a particular control indication to the transmitter module responsive to receiving a first PDU from the second unidirectional serial link, the determination being dependent upon a start of PDU SOP character sequence of the first PDU.

6. The circuit card of claim 5, wherein:

the receiver module is further operable to send a third control indication as the particular control indication to the transmitter module responsive to the first PDU starting with a particular SOP character sequence; and

the transmitter module is operable to delay transmission of the next PDU by a predetermined amount of time responsive to receiving the third control indication from the receiver module.

7. The circuit card of claim 6, wherein the predetermined amount of time is an amount of time taken to transmit one character on the first unidirectional serial link.

8. The circuit card of claim 2, wherein:

the determination of the receiver module is dependent upon an SOP character sequence of a first PDU received from the second unidirectional serial link; and

the transmitter module is further operable to delay transmission of the next PDU by a predetermined amount of time depending upon the particular control indication received from the receiver module.

9. The circuit card of claim 8, wherein the predetermined amount of time is an amount of time taken to transmit one character on the first unidirectional serial link.

10. A receiver module for receiving protocol data units PDUs from unidirectional serial link, comprising:

an input for connecting to the unidirectional serial link;

an output for coupling to a transmitter module; and

a receiver buffer for storing PDUs received from the unidirectional serial link,

wherein the receiver module is operable to determine and send a particular control indication to the transmitter module, the determination depending upon a relationship between a fill level of the receiver buffer and a threshold.

11. The receiver module of claim 10, wherein the receiver module is further operable to determine and send another control indication to the transmitter module responsive to receiving a PDU from the unidirectional serial link, the determination being dependent upon a start of PDU SOP character sequence of the PDU.

12. A transmitter module for transmitting protocol data units PDUs on a unidirectional serial link, comprising:

an output for connecting to the unidirectional serial link; and

an input for coupling to a receiver module,

wherein the transmitter module is operable to determine and use a particular start of PDU SOP character sequence to form a next PDU to be transmitted over the unidirectional serial link, the determination depending upon a particular control indication received from the receiver module.

13. The transmitter module of claim 12, wherein the transmitter module is further operable to delay transmission of the next PDU by a predetermined amount of time responsive to receiving another control indication from the receiver module.

14. A transceiver module for transmitting and receiving protocol data units PDUs over a bidirectional serial link that includes a first unidirectional serial link for communicating PDUs in one direction and a second unidirectional serial link for communicating PDUs in an opposite direction, the transceiver module comprising:

an output for connecting to the first unidirectional serial link;

an input for connecting to the second unidirectional serial link; and

a receiver buffer for storing PDUs received from the second unidirectional serial link,

wherein the transceiver module is operable to determine and use a particular start of PDU SOP character sequence to form a next PDU to be transmitted over the first unidirectional serial link, the determination depending upon a relationship between a fill level of the receiver buffer and a threshold.

15. The transceiver module of claim 14, wherein the transceiver module is further operable to delay transmission of the next PDU by a predetermined amount of time responsive to receiving a PDU from the second unidirectional serial link, the determination being dependent upon an SOP character sequence of the PDU received from the second unidirectional serial link.

16. A circuit card for transmitting and receiving protocol data units PDUs over a bidirectional serial link that includes a first unidirectional serial link for communicating PDUs in one direction and a second unidirectional serial link for communicating PDUs in an opposite direction, the circuit card comprising:

an output for connecting to the first unidirectional serial link;

an input for connecting to the second unidirectional serial link; and

a receiver buffer for storing PDUs received from the second unidirectional serial link,

wherein the circuit card is operable to determine and use a particular start of PDU SOP character sequence to form a next PDU to be transmitted over the first unidirectional serial link, the determination depending upon a relationship between a fill level of the receiver buffer and a threshold.

17. The circuit card of claim 16, wherein the circuit card is further operable to delay transmission of the next PDU by a predetermined amount of time responsive to receiving a PDU from the second unidirectional serial link, the determination being dependent upon an SOP character sequence of the PDU received from the second unidirectional serial link.

18. A method of performing timing compensation on a bidirectional serial link that includes a first unidirectional serial link for communicating protocol data units PDUs in one direction and a second unidirectional serial link for communicating PDUs in an opposite direction, the method comprising the steps of:

receiving a first PDU from the second unidirectional serial link;

storing the first PDU in a receiver buffer;

detecting a fill level of the receiver buffer;

comparing the fill level to a threshold;

determining a particular start of PDU SOP character sequence depending upon a relationship between the fill level and the threshold;

forming a second PDU using the particular SOP character sequence; and

transmitting the second PDU onto the first unidirectional serial link.

19. The method of claim 18, wherein:

the step of receiving comprises detecting an SOP character sequence of the first PDU and determining a type of the SOP character sequence; and

the step of transmitting comprises delaying transmission of the second PDU by a predetermined amount of time responsive to determining that the SOP character sequence is of a given type.

20. The method of claim 19, wherein the predetermined amount of time is an amount of time taken to transmit one character on the first unidirectional serial link.