Memory controller and request scheduling method using request queues and first and second tokens

Abstract

A memory controller includes a plurality of request queues for storing requests transmitted from corresponding host devices among a plurality of host devices, and a token information generation unit for generating information related to the numbers of first and second tokens corresponding to the plurality of respective host devices. The memory controller also includes a request scheduler for selecting repeatedly and sequentially the plurality of request queues, and outputting requests stored in a selected request queue, by using the first and second tokens, wherein the request scheduler outputs one request per one first token and, when first tokens are all consumed, outputs one request per one second token. The scheduler may output requests according to a first-ready first-come first-served (FR-FCFS) rule when using a first token, and output requests according to a first-ready (FR) rule when using a second token. The number of first tokens and second tokens may depend on characteristics of the host devices. A bandwidth control unit may control the number of first and second tokens based on bandwidth. The scheduler may stop outputting requests of a currently selected request queue, and output requests of a request queue corresponding to a top-priority host device.