Memory controller and control method thereof
Provided is a controller which issues a first write command for writing all data of a burst access operation on a memory and a second write command for writing data of a burst access operation on a memory per byte. The controller includes a holding unit configured to hold a plurality of commands requesting access to the memory and a selection unit configured to select, in a case where the holding unit holds the second write command and a command that causes a first time penalty longer than a second time penalty needed between the first write command that is issued first and the second write command that is issued next, the second write command prior to the command.
1. A controller which issues a first write command for writing all data of a burst access operation on a memory and a second write command for writing data of a burst access operation on a memory per byte, the controller comprising:
a holding unit configured to hold a plurality of commands requesting access to the memory; and
a selection unit configured to select, in a case where the holding unit holds the second write command and a command that causes a first time penalty longer than a second time penalty needed between the first write command that is issued first and the second write command that is issued next, the second write command prior to the command, the second write command is a Masked Write command defined in low power double-data-rate standard for dynamic random access memories (DRAMs).
2. The controller according to claim 1 , wherein the first time penalty is a time penalty due to a page-miss.
3. The controller according to claim 1 , wherein the first time penalty is a time penalty due to switching from a read operation to a write operation.
4. The controller according to claim 2 , wherein, among the commands held in the holding unit, the selection unit selects a command that does not cause a page-miss prior to the second write command.
5. The controller according to claim 3 , further comprising a history holding unit configured to hold a memory access history, wherein the selection unit selects a read command prior to the second write command among the commands, in a case where a latest history held in the history holding unit is a read command.
6. The controller according to claim 1 , wherein the holding unit holds the plurality of commands in an order in which the controller has received access requests made to the memory from a master.
7. The controller according to claim 2 ,
wherein the selection unit determines which page of the memory has been activated by referring to a bank status table, and
wherein the selection unit selects the second write command first among the commands, in a case where the holding unit does not hold a command that does not cause a time penalty due to a page-miss.
8. The controller according to claim 1 ,
wherein a time penalty due to a page-miss of a DRAM is longer than a time penalty caused when the Masked Write command is issued after a Write command, and
wherein the selection unit selects a Masked Write command prior to a command that causes a time penalty due to a page-miss.
9. The controller according to claim 1 , wherein the selection unit selects commands in an order in which the controller has received access requests made to the memory from a master, in a case where the holding unit does not hold any Masked Write command.
10. A method of a controller which issues a first write command for writing all data of a burst access operation on a memory and a second write command for writing data of a burst access operation on a memory per byte, the method comprising:
holding a plurality of commands for requesting access to the memory in a holding unit; and
selecting, in a case where the holding unit holds the second write command and a command that causes a first time penalty longer than a second time penalty needed between the first write command that is issued first and the second write command that is issued next, the second write command prior to the command, the second write command is a Masked Write command defined in low power double-data-rate standard for dynamic random access memories (DRAMs).
11. The method according to claim 10 , wherein the first time penalty next is a time penalty due to a page-miss.
12. The method according to claim 10 , wherein the first time penalty is a time penalty due to switching from a read operation to a write operation.
13. The method according to claim 11 , wherein, in the selecting, among the commands, a command that does not cause a page-miss is selected prior to the second write command.
14. The method according to claim 12 further comprising holding a memory access history in a history holding unit, wherein, in the selecting, a read command is selected prior to the second write command among the commands, in a case where a latest history held in the history holding unit is a read command.
15. The method according to claim 10 , wherein the plurality of commands are held in the holding unit in an order in which the controller has received access requests made to the memory from a master.
16. The method according to claim 11 ,
wherein, in the selecting, which page of the memory has been activated is determined by referring to a bank status table, and
wherein, the second write command is selected first among the commands, in a case where the holding unit does not hold a command that does not cause a time penalty due to a page-miss.
17. The method according to claim 1 ,
wherein a time penalty due to a page-miss of a DRAM is longer than a time penalty caused when the Masked Write command is issued after a Write command, and
wherein, in the selecting, a Masked Write command is selected prior to a command that causes a time penalty due to a page-miss.
18. The method according to claim 1 , wherein, in the selecting, commands are selected in an order in which the controller has received access requests made to the memory from a master, in a case where the holding unit does not hold any Masked Write command.