Schneider Optics Web Embedded Server - Manual (Page 85)

Ethernet Developers Guide
840 USE 115 00 Version 1.0 75
The receive state machine maintains a variable which is the number of bytes
received. Initially the receive state machine is in the RX_HEADER state, and the
number of bytes received is zero.
When OnTcpIpRead is called and the receive state is RX_HEADER OnTcpIpRead
calls rx_msg with receive size equal to the header size. On return OnTcpIpRead
examines the number of bytes received. If the number of bytes received is not
equal to the header size, then receive machine remains in the RX_HEADER state,
and OnTcpIpRead returns.
If upon return, the number bytes received is the same size as the header size, then
the header has been received. OnTcpIpRead sets the number of bytes received to
zero, and the receive size is obtained from the header. These two values will be
used the next time rx_msg is called. OnTcpIpRead also obtains the transaction
identifier and the protocol type from the header. If the transaction identifier
matches the transmit request identifier and the protocol type is MODBUS, then
OnTcpIpRead changes the receive state to RX_BODY. However if either
transaction identifier does not match or the protocol is not MODBUS, then
OnTcpIpRead changes the receive state to DUMP_BODY.
When OnTcpIpRead is called and the receive state is RX_BODY, OnTcpIpRead
calls rx_msg with receive size equal to the value obtained from the header. On
return OnTcpIpRead examines the number of bytes received. If the number of
bytes received is not equal to the receive size, then the receive machine remains in
the RX_HEADER state, and OnTcpIpRead returns.
If upon return the number of bytes received is the same as the receive size, then
OnTcpIpRead has read the response to a transaction. OnTcpIpRead saves the
results and invalidates the client area which causes the results to be display.
OnTcpIpRead also changes the transmit state to WAIT_TO_TX, and resets the
state receive state machine by setting the state to RX_HEADER and the number of
bytes received to zero. It then returns.
When OnTcpIpRead is called and the receive state is DUMP_BODY,
OnTcpIpRead calls rx_msg with receive size equal to the value obtained from the
header. On return OnTcpIpRead examines the number of bytes received. If the
number of bytes received is not equal to the receive size, then the receive machine
remains in the RX_HEADER state, and OnTcpIpRead returns.
If upon return the number of bytes received is the same as the receive size, the
OnTcpIpRead has completed reading the message. Since this message does not
correspond to an transaction, the only processing OnTcIpRead performs is
resetting the receive state machine.