Memory system that selects data to be transmitted from a data buffer through a port
A memory system includes a non-volatile memory, a data buffer in which data read out from the nonvolatile memory are stored prior to transmission to an initiator that is requesting the data, a port through which the initiator sends a request for the data and through which the data in the data buffer are transmitted to the initiator. When the port is connected to a first initiator at a time both first data requested by the first initiator and second data requested by a second initiator are stored in the data buffer and the second data become ready for transmission prior to the first data, the second data are transmitted through the port prior to the first data.
1. A memory system, comprising:
a nonvolatile memory;
a data buffer in which data read out from the nonvolatile memory are stored prior to transmission to at least one of a plurality of initiators; and
a controller circuit configured to manage a command-execution list that stores a list of commands received from the initiators, the commands each being associated with data that is stored in the data buffer and has a size greater than a threshold transmission amount, the controller circuit including a plurality of ports to communicate with one of the initiators and a plurality of command-execution circuits, each of which is dedicated to one of the ports and configured to execute one command that is one of the commands stored in the command-execution list, wherein
when one of the ports is connected to a second initiator at a time (A) the amount of first data associated with a first command received from a first initiator and stored in the data buffer for transmission through the one port is greater than the threshold transmission amount and the amount of second data associated with a second command received from the second initiator and stored in the data buffer for transmission through the one port is greater than the threshold transmission amount, the second initiator being different from the first initiator, (B) the amount of the first data in the data buffer became greater than the threshold transmission amount before the amount of the second data in the data buffer became greater than the threshold transmission amount, and (C) a command-execution circuit dedicated to the one port is in a state to execute the first command, the controller circuit (a) searches the command-execution list and finds the second command in the command-execution list, and (b) instructs the command-execution circuit dedicated to the one port to be in a state to execute the second command.
2. The memory system according to claim 1 , wherein
when the one port is connected to no initiator at a time both the amount of the first data stored in the data buffer and the amount of the second data stored in the data buffer become greater than the threshold transmission amount, the controller circuit transmits a connection request through the one port to the first initiator.
3. The memory system according to claim 2 , wherein
when the one port is connected to the first initiator in response to the connection request, the controller circuit transmits the first data through the one port to the first initiator.
4. The memory system according to claim 1 , wherein
each of the ports is connected with an initiator through an expander.
5. The memory system according to claim 1 , wherein
each of the ports is configured to conform to Serial Attached SCSI (SAS) protocol.
6. The memory system according to claim 1 , wherein the controller circuit further includes:
a counter configured to separately count for each of the ports the number of data units transmitted through said each of the ports, wherein
data requested through a port that has the lowest counted number are selected to be read out from the nonvolatile memory and stored in the data buffer next.
7. The memory system according to claim 1 , wherein the controller circuit further includes:
a counter configured to separately count for each of the ports the number of data units stored in the data buffer for transmission through said each of the ports, wherein
data requested through a port that has the lowest counted number are selected to be read out from the nonvolatile memory and stored in the data buffer next.
8. The memory system according to claim 1 , wherein
the threshold transmission amount corresponds to the amount of data requested by one read command.
9. The memory system according to claim 1 , wherein
when one of the ports is connected to no initiator, the controller circuit searches the command-execution list to find an oldest command which was stored in the command-execution list earlier than any other commands which are currently stored in the command-execution list, instructs the command-execution circuit dedicated to the one port to be in a state to execute the oldest command, and transmits a connection request through the one port to an initiator to execute the oldest command.