5-4
Section
Sending Commands From a Host Computer
83
83
if((recvlen = recvfrom(sockfd,fins_resp,MAX_MSG,0,&cv_addr,&addrlen))
<0){
84
if(errno == EINTR)
85
goto CMND_SEND; /
*
RE-SEND FINS COMMAND
*
/
86
err_exit(”receive error”);
87
}
88
else{
89
alarm(0); /
*
STOP RESPONSE MONITOR TIMER
*
/
90
printf(”recv length %d¥n”,recvlen);
91
if(recvlen<14) /
*
ILLEGAL RESPONSE LENGTH CHECK
*
/
92
err_exit(”FINS length error”);
93
if((fins_cmnd[3]!=fins_resp[6])||(fins_cmnd[4]!=fins_resp[7])
94
||(fins_cmnd[5]!=fins_resp[8]))
{ /*
DESTINATION ADDRESS CHECK
*/
95
err_exit(”illegal source address error”);
96
}
97
if(fins_cmnd[9]!=fins_resp[9])
/*
SID CHECK
*/
98
err_exit(”illegal SID error”);
99
}
100
101
102
/
*
CLOSE SOCKET
*
/
103
close(sockfd);
104 }
105 /*
106 *
ERROR PROCESSING FUNCTIONS
107 */
108 err_exit(err_msg)
109 char *err_msg;
110 {
111
printf(”client: %s %x¥n”,err_msg,errno);
112
exit(1);
113 }
114
115 /*
116 *
SIGNAL CAPTURE FUNCTIONS
117 */
118 recv_fail()
119 {
120
printf(”response timeout error ¥n”);
121 }
5-4-4 Delays for Accessing PC Memory
The time for the response to be received after a remote node on the Ethernet
network sends a memory area read or write command to a PC can be calculated
using the following formula. This time does not take network transmission delays
into account, so it may be extended under some operating conditions.
Write command delay time (ms) =
Remote node communications processing time + 4 + (0.011 x number of words
written) + CPU cycle time + CPU data set processing time
Read command delay time (ms) =
Remote node communications processing time + 8 + (0.011 x number of words
read) + CPU cycle time + CPU data read processing time
Note
1. The transfer time may exceed the calculated value due to the actual operat-
ing environment. Factors affecting the transfer time are network traffic, the
window size of each node, Ethernet Unit traffic (e.g., socket services, FTP
server communications, etc.), and the system configuration.
2. The CPU data set processing time is the standard when the peripheral ser-
vice time is set in the CPU Unit System Setup to the default of 4%. As this
value is increased, the processing time is shortened.
This example shows the calculations for a host computer sending a write com-
mand for 256 words to the PC. The standard for the maximum transfer delay
time is as follows when the PC’s CPU cycle time is 10 ms.
Example
