Schneider Optics Web Embedded Server - Manual (Page 84)

Ethernet Developers Guide
74 840 USE 115 00 Version 1.0
The receive state machine (which is described below) processes the response to a
request. When the receive state machine has completed receiving the response, it
changes the transmit state machine from the TX_DONE state to the WAIT_TO_TX
state.
Recall that the TransmitUserRequest saves the time. CSample_View
OnPollInterval uses this saved time to determine if a new request needs to be
transmitted. OnPollInterval is called by MFC architectural framework to process
the WM_POLL_INTERVAL sent when CMainFram class processes the window
timer message, WM_TIMER. OnPollInterval examines the transmit state. If the
transmit state is WAIT_TO_TX, and the elapsed time from the previous transmit
request exceeds the poll interval, then OnPollInterval calls TransmitUserRequest to
start another transaction.
B.11 Receive State Machine
The receive state machine receives a response to a transaction by first reading the
header, determining the size of the rest of the message, and then reading the body
of the message. The different states of the receive state machine are as follows.
z RX_HEADER. In the RX_HEADER state, the receive machine is receiving the
message header.
z
RX_BODY. In the RX_HEADER state, the receive machine is receiving the
response message associated to the requested transaction.
z DUMP_BODY. In the DUMP_BODY state, the receive message is receiving a
message, but there is no associated transaction with respect to this message.
The window socket DLL generates the FD_READ event whenever there is data to
be read. If only part of the data is read, it generates another event. CSample_View
OnTcpIpRead function processes the FD_READ event, and drives the receive
state machine.
When a FD_READ event is generated it is possible that the complete message is
not present. The remote node may have attempted to send a 100 byte response,
but the transport system may have only had buffer space to transmit three bytes.
The receiver will get a FD_READ for the three bytes. OnTcpIpRead calls
CSample_View rx_msg to read the receive data into the buffer. There are three
parameters to rx_msg. The first parameter is a pointer to a receive buffer. The
second input parameter is the receive size. The third parameter is both an input
and output parameter. On both input and output the third parameter is the number
of bytes read. These parameters allow the processing of a partially received
message.