User`s guide

5: ICP Packet Formats

DC 900-1516D 85

5.2 DLI Optional Arguments

A program using the full DLI library interface to an ICP on a Freeway server is not

allowed to write information directly to the ICP and Protocol headers. Instead, Freeway

users place the desired values in a

DLI_OPT_ARGS structure and the DLI write call

moves these values into the proper places in the ICP and Protocol headers. The same

applies to DLI read calls. Information from received packets is taken from the ICP and

protocol headers and placed in the

DLI_OPT_ARGS structure where the program can

read it.

Although the DLI library is not used by programs accessing Protogate’s standard device

driver, it is mentioned here to allow embedded ICP users to see the similarity in packet

format when reading Freeway documents. Figure 5–2 shows the

DLI_OPT_ARGS struc-

ture as it is used in a Freeway environment. Note that the

ICP_PACKET structure differs

only slightly from the

DLI_OPT_ARGS structure. The ICP_PACKET structure omits the

three Freeway server header fields (

usFWPacketType, usFWCommand, and usFWStatus)

and adds one new field (

usICPCount). See Tabl e 5 –1 for a comparison between the

header fields in the