Communication system, communication device, integrated circuit, and communication method

A communication device included in a plurality of communication devices that are connected with one another in a ring via a serial link and that constitute a communication system, the serial link being made up of (i) a downlink, which is a part of the serial link that extends from a master communication device to a slave communication device, the master communication device and the slave communication device being included in the plurality of communication devices, and (ii) an uplink, which is a part of the serial link that extends from the slave communication device to the master communication device, the communication device comprising:

• a command processing unit configured to issue, to a partner device that is one of the plurality of communication devices with which the communication device performs communication, (i) a standby packet for causing one or more of the plurality of communication devices connected to one of the downlink and the uplink that is not used for data packet transfer to switch to standby mode, and (ii) a loopback packet for causing one or more of the plurality of communication devices connected to one of the downlink and the uplink that is used for the data packet transfer to switch to loopback mode;
• a data transfer unit configured to transfer a write data packet to be written via the downlink, and to transfer a read data packet to be read via the uplink;
• a packet relay unit configured to, in accordance with a destination of a packet input to the communication device, relay the input packet to one of the plurality of communication devices that immediately succeeds the communication device in the ring;
• and
• a standby control unit configured to (i) when the input packet relayed by the packet relay unit is the standby packet, cause the communication device to switch to the standby mode, and (ii) when the input packet relayed by the packet relay unit is the loopback packet, cause the communication device to switch to the loopback mode.

An integrated circuit used by a communication device included in a plurality of communication devices that are connected with one another in a ring via a serial link and that constitute a communication system, the serial link being made up of (i) a downlink, which is a part of the serial link that extends from a master communication device to a slave communication device, the master communication device and the slave communication device being included in the plurality of communication devices, and (ii) an uplink, which is a part of the serial link that extends from the slave communication device to the master communication device, the integrated circuit comprising:

• a command processing circuit configured to issue, to a partner device that is one of the plurality of communication devices with which the communication device performs communication, (i) a standby packet for causing one or more of the plurality of communication devices connected to one of the downlink and the uplink that is not used for data packet transfer to switch to standby mode, and (ii) a loopback packet for causing one or more of the plurality of communication devices connected to one of the downlink and the uplink that is used for the data packet transfer to switch to loopback mode;
• a data transfer circuit configured to transfer a write data packet to be written via the downlink, and to transfer a read data packet to be read via the uplink;
• a packet relay circuit configured to, in accordance with a destination of a packet input thereto, relay the input packet to one of the plurality of communication devices that immediately succeeds the communication device in the ring;
• and
• a standby control circuit configured to (i) when the input packet relayed by the packet relay circuit is the standby packet, cause the communication device to switch to the standby mode, and (ii) when the input packet relayed by the packet relay circuit is the loopback packet, cause the communication device to switch to the loopback mode.

A communication method used in a communication system including a first communication device and a plurality of second communication devices, the first communication device and the second communication devices being connected with one another in a ring via a serial link, wherein

• the communication method causes the first communication device to perform the steps of:
• when a downlink is not used for data packet transfer, issuing a standby packet to a partner device that is one of the second communication devices with which the first communication device performs communication, the downlink being a part of the serial link extending from the first communication device to the partner device;
• and
• transmitting a write data packet to be written via the downlink and receiving a read data packet to be read via an uplink, which is a part of the serial link extending from the partner device to the first communication device, and the communication method causes each of the second communication devices to perform the steps of:
• issuing the standby packet to the first communication device when the uplink is not used for the data packet transfer and a respective one of the second communication devices is the partner device;
• receiving the write data packet via the downlink and transmitting the read data packet via the uplink;
• in accordance with a destination of a packet input to a respective one of the second communication devices, relaying the input packet to one of the first and second communication devices that immediately succeeds a respective one of the second communication devices in the ring;
• and
• causing a respective one of the second communication devices to switch to standby mode when the input packet that has been relayed in a respective one of the second communication devices is the standby packet.