Method and apparatus for using a control signal on a packet based communication link

A method for communicating in a computer system having a communication link including a control signal and a unidirectional first data portion transferring control packets and data packets from a first to a second node of the communication link, the method comprising:

• distinguishing between control packets and data packets being transferred over the communication link using the control signal;
• transferring a first portion of one of the control packets over the first data portion with the control line at a first voltage level;
• changing the control line to a second voltage level during transfer of the control packet;
• suspending transfer of the control packet in synchronism with changing the control line to the second voltage level to thereby insert a stall in transferring the control packet;
• and
• subsequently changing the control line back to the first voltage level and resuming transfer of a second portion of the control packet.

A method for communicating in a computer system having a communication link including a control signal and a first data portion of the communication link transferring data from a first to a second node on the communication link, the method comprising:

• transferring a first control packet having a plurality of bytes of control information over the first data portion of the communication link, transfer of the control packet being indicated by the control line being at a first value;
• subsequently transferring a first portion of a data packet associated with tile first control packet, the data packet having a plurality of bytes, transfer of the first portion of the data packet being indicated by the control line being at a second value;
• changing the control line back to the first value during transfer of the data packet;
• suspending transfer of the data packet in synchronism with changing the control line back to the first value;
• transferring a second control packet over the first data portion of the communication link subsequent to the suspending of the data packet;
• and
• transferring a second portion of the data packet subsequent to transfer of the second control packet, transfer of the second portion of the data packet being indicated by the control line being at the second value.

A computer system, comprising:

• a first node;
• a second node;
• a communication link connecting the first and second nodes, the communication link including, a first data portion and a first control line, the first data portion carrying data packets of multiple bytes and control packets from the first to the second node;
• wherein the first control line is at a first value during transfer of the control packets and wherein the first control line is at a second value during transfer of the data packets;
• and wherein control logic in the first node is responsive to suspend transfer of one of the data packets and to place the control line at the first value indicative of suspending transfer of the one data packet, the control logic being further responsive to insert a control packet on the first data portion and to resume the data packet transfer on completion of the transfer of the inserted control packet.