Data Handling And Data Segmentation In Tcp Socket Interface Transmission And Reception - Toshiba V Series User Manual

Chapter 6 Socket Interface Communication
6.2.2 Data handling and data segmentation in TCP socket interface
transmission and reception
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(7) If the size of the data transmitted in a single operation is larger than the size specified
for the received data in the receive request program, the receive request will end with
an error. The received data is stored in the reception data storage area of the S
controller, but from the beginning of the received data up to the reception data size
only. The excess data will not be transferred to the S controller nor remained on the
EN311 (it will be discarded).
(1) When using the TCP socket for data transmission, the data transmitted in a single
operation is handled by the receiving EN311 as one section of a continuous data
stream that comes from the sender (see Figure 6-6).
In this technique, the data is not handled as a single unit, as it is in UDP socket.
(2) The amount of data transmitted to the S controller from the TCP socket due to a S
controller receive request will vary depending on both the timing with which the S
controller issues the receive request, and the timing with which the data arrives at the
TCP socket.
(3) In the EN311 TCP socket, up to 5840 bytes of received data can be stored per
socket. Also note that up to 2000 bytes of data can be transferred to the S controller
for a single receive request.
For example, if the remote node sends 8000 bytes at a time, then the amount of
received data per socket may be either 800, 1600, 2400, 3200, or 4000 bytes. If the
amount of received data is 800 or 1600 bytes, those 800 or 1600 bytes can be
acquired by a receive request from the S controller. In cases where the amount of
received data is 2400, 3200, or 4000 bytes, 2000 bytes will be transferred by the first
receive request from the S controller, and the remaining 400, 1200, or 2000 bytes
can be transferred by issuing another receive request from the S controller.
(4) Therefore, to handle one unit of transmitted data as a single unit of data on the
receiving side as well, users must analyze both the data format (head/tail delimiting
codes, data sequencing) and the amount of data to be transmitted during the system
design stage, and provide routines to decode the transmitted data in the receiving S
controller user software.
(5) When the S controller user program issues the receive request, if amount of data
received by the socket is larger than the amount of data specified by the reception
data size, then only the reception data size of the received data from the beginning
will be transferred to the S controller.
The remaining data will be stored in the EN311. Issue another receive request to
receive the remaining data.
(6) When the S controller user program issues the receive request, if amount of data
received by the socket is smaller than the amount of data specified by the reception
data size, all of the received data is transferred to the S controller.
(7) Make sure to prepare the register area in which the transfer data is stored with
"receive data size + 1 word". If the register area in which the transferred data is
stored is smaller than this size, the transferred data will overwrite the contents of the
following registers.
Ethernet module User's Manual