DRAM controller that forces a refresh after a failed refresh request
A refresh controller transmits two refresh request signals of a first request signal which indicates a time at which a refresh operation of a DRAM may be performed and a second request signal which indicates a time at which a refresh operation of the DRAM must be performed, to an arbitrator. On the other hand, also transfer request signals each of which requests a data transfer are transmitted from plural data transfer parts, respectively, to the arbitrator. If no transfer request signal is input when a first request signal is input to the arbitrator, a refresh operation of the DRAM is performed. As a result, a refresh operation is performed when the crowding level of a bus is relatively low. This improves an efficiency in a data transfer.
1. A memory controller for controlling a DRAM, comprising:
a first generator that generates and transmits a signal indicative of a crowding level of a bus used for a data transfer with said DRAM;
a refresh request unit configured to generate a reference signal with a predetermined generation period and to transmit a first refresh request and a second refresh request, said first refresh request being transmitted during said predetermined generation period, and said second refresh request being transmitted in response to the generation of the reference signal when a refresh operation of said DRAM has not been performed during the predetermined generation period; and
an arbitrator that adjusts a time to perform the refresh operation of said DRAM based on said signal indicative of said crowding level input from said first generator,
wherein said arbitrator instructs said DRAM to perform the refresh operation in response to said arbitrator receiving said second refresh request, and
said arbitrator instructs said DRAM to perform the refresh operation when said arbitrator receives said first refresh request and when said signal indicative of said crowding level is not input.
2. The memory controller according to claim 1 , wherein
said first generator generates said signal indicative of said crowding level based on an amount of data stored in a memory used for a data transfer with said DRAM.
3. The memory controller according to claim 1 ,
wherein when said predetermined generation period of said reference signal is represented as “Ta”, a finite period during which said refresh operation is allowed to be instructed to be performed prior to generation of said reference signal is represented as “Td”, the longest finite period that each of memory cells in said DRAM is allowed to spend while storing data with no refresh operation being performed is represented as “MT”, and the number of word lines of said DRAM is represented as “n”, Ta satisfies a relationship in a formula: Ta≦MT/n−Td/n.
4. The memory controller according to claim 1 , further comprising
a setting part that sets a starting point of said predetermined generation period of said reference signal at a time of a refresh operation of said DRAM.