Method and system for time synchronization among systems using parallel sysplex links

A synchronization system for providing time synchronization among first and second computer systems, each of the computer systems including hardware, a clock having a clock value, operating system software, and a layer of microcode operating between said hardware and said operating system software for interacting with said hardware, the synchronization system comprising:

• a first non-volatile memory unit and one or more processing units on the first computer system;
• and
• a second non-volatile memory unit and one or more processing units on the second computer system;
• the first non-volatile memory unit storing first code means within the microcode of the first computer system to obtain a first timestamp from the clock of the first computer system;
• the one or more processing units on the first computer system being configured to send the first timestamp to the second computer system;
• the second non-volatile memory unit storing second code means within the microcode of the second computer system to provide a second timestamp and a third timestamp in response to the second computer system receiving the first timestamp;
• the one or more processing units on the second computer system being configured to send the second and third timestamps to the first computer system
• wherein said first code means obtains a fourth timestamp from the clock of the first computer system in response to the first computer system receiving the second and third timestamps;
• the one or more processing units on the first computer system being further configured for using said first, second, third and fourth time stamps to determine a time difference between the clock values of the first and second computer systems;
• and for adjusting a timing synchronization among said first and second computer systems on the basis of said determined time difference between the clock values of the first and second computer systems by using said determined time difference to converge the clock values of the first and second computer systems;
• and wherein:
• a specified transmission time is used to transmit the first, second and third timestamps between the first and second computer systems;
• the using said first, second, third and fourth timestamps to determine a time difference between the clock values of the first and second computer systems includes determining said time difference independent of the transmission time to transmit the first, second and third timestamps between the first and second computer systems;
• the first timestamp represents a time t0 at which the first timestamp is sent to the second computer system;
• the second timestamp represents a time t1 at which the first timestamp is received by the second computer system;
• the third timestamp represents a time t2 at which the second and third timestamps are sent to the first computer system;
• the fourth timestamp represents a time t3 at which the first computer system receives the second and third timestamps;
• determining a time difference between the clock values of the first and second computer systems includes:
• identifying a defined equation expressing said time difference between the clock values of the first and second computer systems as a function of t0, t1, t2 and t3 and independent of the transmission time to transmit the first, second and third timestamps between the first and second computer systems;
• using said defined equation to determine the time difference between the clock values of the first and second computer systems independent of the transmission time to transmit the first, second and third timestamps between the first and second computer systems;
• and
• said defined equation is:
• d=½[(t1+t2)−(t3+t0)],
• where d is the time difference between the clock values of the first and second computer systems.

A program storage device readable by machine, including a program of instructions tangibly embodied in the program storage device and executable by the machine to perform method steps for providing time synchronization among first and second computer systems, each of the computer systems including hardware, a clock having a clock value, operating system software, and a layer of microcode operating between said hardware and said operating system software for interacting with said hardware, the method steps comprising:

• using the microcode of the first computer system to obtain a first timestamp from the clock of the first computer system;
• sending the first timestamp to the second computer system;
• in response to the second computer system receiving the first timestamp, using the microcode of the second computer system to provide a second timestamp and a third timestamp;
• in response to the first computer system receiving the second timestamp and the third timestamp, using the microcode of the first computer system to obtain a fourth timestamp from the clock of the first computer system;
• using said first, second, third and fourth timestamps to determine a time difference between the clock values of the first and second computer systems;
• and
• adjusting a timing synchronization among said first and second computer systems on the basis of said determined time difference between the clock values of the first and second computer systems by using said determined time difference to converge the clock values of the first and second computer systems;
• and wherein:
• a specified transmission time is used to transmit the first, second and third timestamps between the first and second computer systems;
• the using said first, second, third and fourth timestamps to determine a time difference between the clock values of the first and second computer systems includes determining said time difference independent of the transmission time to transmit the first, second and third timestamps between the first and second computer systems;
• the first timestamp represents a time t0 at which the first timestamp is sent to the second computer system;
• the second timestamp represents a time t1 at which the first timestamp is received by the second computer system;
• the third timestamp represents a time t2 at which the second and third timestamps are sent to the first computer system;
• the fourth timestamp represents a time t3 at which the first computer system receives the second and third timestamps;
• determining a time difference between the clock values of the first and second computer systems includes:
• identifying a defined equation expressing said time difference between the clock values of the first and second computer systems as a function of t0, t1, t2 and t3 and independent of the transmission time to transmit the first, second and third timestamps between the first and second computer systems;
• using said defined equation to determine the time difference between the clock values of the first and second computer systems independent of the transmission time to transmit the first, second and third timestamps between the first and second computer systems;
• and
• said defined equation is:
• d=½[(t1+t2)−(t3+t0)],
• where d is the time difference between the clock values of the first and second computer systems.