Method and apparatus for preserving loop fairness with dynamic half-duplex

A communications channel system for preserving loop fairness comprising:

• a first channel node having a first port for attachment to a serial communications channel, wherein the first port arbitrates for control of that port's attached communications channel;
• a fairness-preserving apparatus operatively coupled to the first port, wherein the first port arbitrates for control of a loop of the communications channel and, after control is achieved, the fairness-preserving apparatus causes control of the communications channel to be released based at least in part on whether a first predetermined amount of data has been transferred between the first port and the communications channel;
• a first counter that monitors the amount of data that has been transferred;
• a first comparator circuit operatively coupled to the first counter that causes control of the communications channel to be released based at least in part on whether the amount of data monitored by the first counter reaches the first predetermined amount of data;
• a second counter that monitors the amount of data that remains to be transferred;
• and
• a second comparator circuit operatively coupled to the second counter that inhibits release of control of the communications channel based at least in part on whether the amount of data monitored by the second counter is less than a second predetermined amount of data.

A communications channel system for preserving loop fairness comprising:

• a first channel node having a first port for attachment to a serial communications channel, wherein the first port arbitrates for control of that port's attached communications channel;
• a fairness-preserving apparatus operatively coupled to the first port, wherein the first port arbitrates for control of a loop of the communications channel and, after control is achieved, the fairness-preserving apparatus causes control of the communications channel to be released based at least in part on whether a first predetermined amount of data has been transferred between the first port and the communications channel;
• a magnetic-disc-storage drive operatively coupled to the first channel node;
• and
• a computer system having a second channel node, wherein the second channel node is operatively coupled to the first channel node in a loop in order to transfer data between the first and second channel nodes through the serial communications channel.

A communications method for use with a node having a first port for attachment to a serial communications channel, the method comprising steps of:

• (a) arbitrating for control of a loop of the first port's serial communications channel;
• and
• (b) releasing control of the communications channel based at least in part on whether a first predetermined amount of data has been transferred, the first predetermined amount of data being determined by:
• (b)(i) monitoring the number of frames that have been transferred to provide a first value;
• and
• (b)(ii) comparing the first value to the first predetermined amount of data.

A communications channel system for preserving loop fairness comprising:

• a serial communications channel;
• a first channel node having a first port that is operatively coupled to the serial communications channel;
• a second channel node having a second port that is operatively coupled to the serial communications channel;
• and
• a fairness-preserving apparatus operatively coupled to the second port of the second node, wherein the first port of the first channel node arbitrates for control of a loop of the communications channel and, after control is achieved, control is maintained while:
• the second port of the second node transmits an indication of space available to receive data in the second node, the first port of the first node transmits a first amount of data to the second port of the second node and an indication that the first port of the first node is ready to receive data and an indication of space available to receive data in the first node, and the second port of the second node transmits up to a second amount of data to the first port of the first node, and wherein the fairness preserving apparatus causes control of the communications channel to be released based at least in part on whether a first predetermined amount of data has been transmitted from the second node to the first node.