Method for Scheduling Memory Refresh Operations Including Power States

A method for performing refresh operations on a rank of memory devices, said method comprising:

• in response to a completion of a memory operation, determining whether or not a refresh backlog count is greater than a first predetermined value;
• in a determination that said refresh backlog count is greater than said first predetermined value, performing a refresh operation as soon as possible;
• in a determination that said refresh backlog count is not greater than said first predetermined value, determining whether or not said refresh backlog count is less than a second predetermined value;
• in a determination that said refresh backlog count is not less than said second predetermined value, determining whether or not said refresh backlog count is less than a third predetermined value and said rank of memory devices is in a powered down state;
• in a determination that said refresh backlog count is less than said third predetermined value and said rank of memory devices is in a powered down state, setting an Idle Count threshold value to a maximum value such that a refresh operation will be performed after a maximum delay time;
• and
• in a determination that said refresh backlog count is not less than said third predetermined value or said rank of memory devices is not in a powered down state, setting said Idle Count threshold value based on the slope of an Idle Delay Function such that a refresh operation will be performed accordingly.