Method and apparatus to reduce serial communications path connection overhead

Abstract

Control of a loop of a fiber-channel arbitrated-loop serial communications channel is maintained (i.e., the loop connection is held open) as long as a minimum amount of data, which optionally is determined by programming (called a “programmable amount of data”), is available for transmission, in order to reduce the overall amount of time spent arbitrating for control of the loop. The improved communications channel system includes a channel node having one or more ports, each port supporting a fiber-channel arbitrated-loop serial communications channel loop, wherein each port arbitrates for control of that port's attached channel loop. The system also includes an arbitration-and-control apparatus to reduce arbitrated-loop overhead, wherein control of the channel loop, once control is achieved by arbitration, is maintained by the arbitration-and-control apparatus as long as a predetermined amount of data is available within control of the node. In addition, a method to reduce arbitrated-loop overhead is described.Control of a serial communications path is maintained ( i.e., the connection is held open ) as long as a minimum amount of data, which optionally is determined by programming ( called a “programmable amount of data” ) , is available for transmission, in order to reduce the overall amount of time spent opening the connection to the serial communications path. The system includes a serial device having n ports ( where n equals one or more ) , each port supporting a serial communications path. Each port arbitrates for control of that port's attached serial communications path. The system also includes an arbitration - and - control apparatus, wherein control of the serial communications path, once control is achieved, is maintained by the arbitration - and - control apparatus as long as a predetermined amount of data is available within control of the serial device. In addition, a method to reduce connection overhead is described.

1. A communications channel system for reducing arbitration overhead comprising:
 a first channel node having a first port and a second port, each port supporting a fiber-channel arbitrated-loop serial communications channel, wherein each one of the ports arbitrates for control of that port's attached communications channel; and  
 an arbitration-and-control apparatus to reduce arbitrated-loop overhead, wherein the arbitration-and-control apparatus arbitrates for control of a loop of the communications channel and, after control is achieved, maintains control of the communications channel as long as at least a first predetermined amount of data is available within control of the channel node, wherein the first predetermined amount of data within control of the channel node includes at least some data not available for transfer to the communications channel.  
 
     
     
       2. The system according to  claim 1 , further comprising:
 a channel-node circuit chip, the chip having an on-chip data buffer, wherein the first predetermined amount of data includes a predetermined amount of on-chip data within the on-chip data buffer currently available for transfer to the communications channel; and  
 an off-chip memory, wherein the first predetermined amount of data further includes a predetermined amount of off-chip data, which is to be transferred to the communications channel but is currently not available for transfer, within the off-chip memory that is distinct from the predetermined amount of on-chip data.  
 
     
     
       3. The system according to  claim 2 , wherein the predetermined amount of on-chip data includes a programmable amount of data. 
     
     
       4. The system according to  claim 2 , wherein the predetermined amount of off-chip data includes a programmable amount of data. 
     
     
       5. The system according to  claim 2 , wherein the predetermined amount of on-chip data includes a programmable amount of data, the predetermined amount of off-chip data includes a programmable amount of data, and the predetermined amount of off-chip data is a different amount than the predetermined amount of on-chip data. 
     
     
       6. The system according to  claim 5 , further comprising:
 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 fiber-channel loop in order to transfer data between the first and second channel nodes through the fiber-channel arbitrated-loop serial communications channel.  
 
     
     
       7. The system according to  claim 1 , further comprising:
 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 fiber-channel loop in order to transfer data between the first and second channel nodes through the fiber-channel arbitrated-loop serial communications channel.  
 
     
     
       8. The system according to  claim 1 , wherein
 the arbitration-and-control apparatus, for at least one transfer operation, delays the start of the transfer operation until after a second predetermined amount of data is available for transfer.  
 
     
     
       9. The system according to  claim 1 , further comprising:
 a channel-node circuit chip, the chip having an on-chip data buffer; and  
 an off-chip memory operatively coupled to supply data to the channel-node circuit chip, wherein the communications channel is an fiber channel arbitrated loop, and the loop is held open if at least one-half a frame of data is contained in on-chip data-frame buffer, and at least one frame of data are contained in off-chip memory.  
 
     
     
       10. A disc drive comprising:
 a rotatable disc;  
 a transducer in transducing relationship to the rotating disc;  
 a channel node having a first port and a second port, each port supporting a fiber-channel arbitrated-loop communications channel, each communications channel including a cyclic-redundancy code within data transmissions on the communications channel, the channel node operatively coupled to the transducer to communicate data; and  
 an arbitration-and-control apparatus operatively coupled to the channel node to reduce arbitrated-loop overhead, wherein the arbitration-and-control apparatus arbitrates for control of a loop of the communications channel and, after control is achieved, maintains control of the communications channel as long as at least a first predetermined amount of data is available within control of the channel node, wherein the first predetermined amount of data within control of the channel node includes at least some data not available for transfer to the communications channel.  
 
     
     
       11. The disc drive according to  claim 10 , further comprising:
 a channel-node circuit chip within the channel node, the chip having an on-chip data buffer, wherein the predetermined amount of data includes a predetermined amount of on-chip data within the on-chip data buffer currently available for transfer to the communications channel; and  
 an off-chip memory, wherein the predetermined amount of data further includes a predetermined amount of off-chip data, which is to be transferred to the communications channel but is currently not available for transfer, within the off-chip memory that is distinct from the predetermined amount of on-chip data.  
 
     
     
       12. A communications method comprising steps of:
 (a)(I) arbitrating for control of a loop of a fiber-channel arbitrated-loop serial communications channel; and  
 (b) maintaining control of the loop of the communications channel as long as a first predetermined minimum amount of data is available within control of the channel node, wherein the first predetermined amount of data within control of the channel node includes at least some data not currently available for transfer to the communications channel, whereby arbitrated-loop overhead is reduced.  
 
     
     
       13. The method according to  claim 12 , wherein the maintaining step (b) further includes steps of:
 (b)(I) determining an on-chip amount of data available in a channel-node circuit chip;  
 (b)(ii) determining an off-chip amount of data available in an off-chip memory; and  
 (b)(iii) comparing the on-chip amount of data available to a predetermined minimum-required amount of on-chip data;  
 (b)(iv) comparing the off-chip amount of data available to a predetermined minimum-required amount of off-chip data; and  
 (b)(v) maintaining control of the loop based on these comparisons.  
 
     
     
       14. The method according to  claim 13 , wherein the maintaining step (b) further includes a step of
 (b)(vi) programmably changing the predetermined minimum-required amount of on-chip data and the predetermined minimum-required amount of off-chip data.  
 
     
     
       15. The method according to  claim 13 , wherein the maintaining step (b) further includes a step of
 (b)(vii) programmably changing the predetermined minimum-required amount of off-chip data to a different amount than the predetermined minimum-required amount of on-chip data.  
 
     
     
       16. The method according to  claim 13 , wherein the maintaining step (b) further includes a step of
 (b)(viii) programmably changing the predetermined minimum-required amount of off-chip data.  
 
     
     
       17. The method according to  claim 12 , further comprising a step of
 (c) transferring data through the fiber-channel arbitrated-loop serial-communications channel between a magnetic-disc-storage drive that is 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 by the fiber-channel arbitrated-loop serial-communications channel.  
 
     
     
       18. The method according to  claim 12 , further comprising a step of
 (d) beginning a transfer operation only after a second predetermined amount of data is available for transfer.  
 
     
     
       19. A fiber-channel node controller system for reducing arbitration overhead comprising:
 a first channel node having a first port and a second port, each port supporting a fiber-channel arbitrated-loop serial communications channel, each communications channel including a cyclic-redundancy code within data transmissions on the communications channel; and  
 arbitration-and-control means for arbitrating for control of a loop of the communications channel and, after control is achieved, maintaining control of the communications channel as long as at least a first predetermined amount of data is available within control of the channel node, wherein the first predetermined amount of data within control of the channel node includes at least some data not available for transfer to the communications channel, thus reducing arbitrated-loop overhead.  
 
     
     
       20. A system, comprising:
   a first serial device having n ports, each port supporting a serial communications path; and        an arbitration - and - control apparatus configured to arbitrate for control of the serial communications path and, after control is achieved, maintain control of the serial communications path as long as at least a first predetermined amount of data is available within control of the first serial device, wherein the first predetermined amount of data within control of the first serial device includes at least some data not available for transfer to the serial communications path.     
     
     
       21. The system of  claim 20  wherein n comprises one or more. 
     
     
       22. The system of  claim 20 , further comprising:
   a serial device circuit chip, the chip having an on - chip data buffer, wherein the first predetermined amount of data includes a predetermined amount of on - chip data within the on - chip data buffer currently available for transfer to the serial communications path; and        an off - chip memory, wherein the first predetermined amount of data further includes a predetermined amount of off - chip data, which is to be transferred to the serial communications path but is currently not available for transfer, within the off - chip memory that is distinct from the predetermined amount of on - chip data.     
     
     
       23. The system of  claim 22 , wherein the predetermined amount of on- chip data includes a programmable amount of data.   
     
     
       24. The system of  claim 22 , wherein the predetermined amount of off- chip data includes a programmable amount of data.   
     
     
       25. The system of  claim 22 , wherein the predetermined amount of on- chip data includes a programmable amount of data, the predetermined amount of off - chip data includes a programmable amount of data, and the predetermined amount of off - chip data is a different amount than the predetermined amount of on - chip data.   
     
     
       26. The system of  claim 25 , further comprising:
   a data storage device operatively coupled to the first serial device; and        a computer system having a second serial device, wherein the second serial device is operatively coupled to the first serial device in order to transfer data between the first and second serial devices through the serial communications path.     
     
     
       27. The system of  claim 20 , wherein the arbitration- and - control apparatus, for at least one transfer operation, delays the start of the transfer operation until after a second predetermined amount of data is available for transfer.   
     
     
       28. The system of  claim 20 , further comprising:
   a serial device circuit chip, the chip having an on - chip data buffer; and        an off - chip memory operatively coupled to supply data to the serial device circuit chip, wherein the communications path is held open if at least one - half a packet of data is contained in the on - chip data buffer, and at least one packet of data are contained in off - chip memory.     
     
     
       29. A data storage system, comprising:
   a storage medium;        a serial device having n ports, each port supporting a serial communications path that carries a data protection code within data transmissions on the serial communications path, the serial device operatively coupled to communicate data to and from the storage medium; and        an arbitration - and - control apparatus operatively coupled to the serial device to reduce connection overhead, wherein the arbitration - and - control apparatus arbitrates for control of the serial communications path and, after control is achieved, maintains control of the serial communications path as long as at least a first predetermined amount of data is available within control of the serial device, wherein the first predetermined amount of data within control of the serial device includes at least some data not available for transfer to the serial communications path.     
     
     
       30. The data storage system according to  claim 29 , further comprising:
   a serial device circuit chip within the serial device, the chip having an on - chip data buffer, wherein the predetermined amount of data includes a predetermined amount of on - chip data within the on - chip data buffer currently available for transfer to the serial communications path; and        an off - chip memory, wherein the predetermined amount of data further includes a predetermined amount of off - chip data, which is to be transferred to the serial communications path but is currently not available for transfer, within the off - chip memory that is distinct from the predetermined amount of on - chip data.     
     
     
       31. A method, comprising:
   arbitrating for control of a serial communications path; and        maintaining control of the serial communications path as long as a first predetermined minimum amount of data is available within control of a first serial device, wherein the first predetermined amount of data within control of the first serial device includes at least some data not currently available for transfer to the serial communications path.     
     
     
       32. The method according to  claim 31 , wherein maintaining control further comprises:
   determining an on - chip amount of data available in a serial device circuit chip;        determining an off - chip amount of data available in an off - chip memory;        comparing the on - chip amount of data available to a predetermined minimum - required amount of on - chip data;        comparing the off - chip amount of data available to a predetermined minimum - required amount of off - chip data; and        maintaining control of the serial communications path based on the comparisons.     
     
     
       33. The method according to  claim 32 , wherein maintaining control of the serial communications path as long as a first predetermined minimum amount of data is available, further comprises:
   programmably changing the predetermined minimum - required amount of on - chip data and the predetermined minimum - required amount of off - chip data.     
     
     
       34. The method according to  claim 32 , wherein maintaining control of the serial communications path as long as a first predetermined minimum amount of data is available, further comprises:
   programmably changing the predetermined minimum - required amount of off - chip data to a different amount than the predetermined minimum - required amount of on - chip data.     
     
     
       35. The method according to  claim 32 , wherein maintaining control of the serial communications path as long as a first predetermined minimum amount of data is available, further comprises:
   programmably changing the predetermined minimum - required amount of off - chip data.     
     
     
       36. The method according to  claim 31 , further comprising:
   transferring data through the serial - communications path between a data storage device that is operatively coupled to the first serial device and a computer system having a second serial device, wherein the second serial device is operatively coupled to the first serial device by the serial - communications path.     
     
     
       37. The method according to  claim 31 , further comprising:
   beginning a transfer operation only after a second predetermined amount of data is available for transfer.     
     
     
       38. A system, comprising:
   a first serial device having n ports, each port supporting a serial communications path, each serial communications path including a data protection code within data transmissions on the serial communications path; and        arbitration - and - control means for arbitrating for control of the serial communications path and, after control is achieved, maintaining control of the serial communications path as long as at least a first predetermined amount of data is available within control of the serial device, wherein the first predetermined amount of data within control of the serial device includes at least some data not available for transfer to the serial communications path.     
     
     
       39. A system comprising:
   a first serial device having n ports, each port supporting a serial communications path, each serial communications path including a data protection code within data transmissions on the serial communications path; and        arbitration - and - control means for arbitrating for control of the serial communications path and, after control is achieved, maintaining control of the serial communications path as long as at least a first predetermined amount of data is available within control of the serial device, wherein the first predetermined amount of data within control of the serial device includes at least some data not available for transfer to the serial communications path, thus reducing connection overhead.