Requestors issue access requests to a memory controller. The access requests issued are accumulated in a command queue of the memory controller. When the amount of access requests accumulated in the command queue is smaller than or equal to a threshold, a free pass (FP) is granted to specified requesters. When issuing access requests, requesters request and acquire tokens before issuing the access requests if they have no FP granted. If the requesters have an FP, they simply issue the access requests.