Echelon OpenLDV - Manual (Page 85)

OpenLDV Programmer’s Guide 77
Uplink Commands
An uplink command is a message read from a network interface by an OpenLDV
application with the ldv_read() function:
• The OpenLDV interface passes certain network management messages to
the OpenLDV application for processing.
• The network interface passes uplink application messages, network
variable updates, and network variable poll requests to the OpenLDV
interface when they are received from the network.
• The network interface also passes completion events to the OpenLDV
interface at the conclusion of every downlink message initiated with the
niCOMM network interface command. If the downlink message was a
request message, the network driver also passes up any responses it
might have received from the network.
• Layer 2 network interfaces send error codes for physical packet errors.
There are two classes of uplink communication:
• Immediate commands are sent to the OpenLDV application by the
network interface to indicate the current operational status of the
network interface.
• Local network management responses are sent to the OpenLDV
application when it issues a local network management request to the
network interface.
Commands for Layer 5 devices that can be used with a specified queue include
niCOMM for messages received from the network, and niNETMGMT for local
network management operation messages received from the network interface.
Local network management messages use the Layer 5 buffer structure,
regardless of which layer the network interface uses for network messages.
Immediate Commands
Immediate commands can be sent to the OpenLDV interface using the
ldv_write() function, and received using the ldv_read() function. Most
immediate commands are just two bytes long. This includes a command byte
followed by a trailing zero, which indicates there is no data payload for the
command. However, some commands, such as niXDRVESC (xDriver escape
command), do require a data payload.
The OpenLDV Developer Example also includes an example implementation of a
network interface API. The NiSendImmediate() function, which is part of this
example API, can be used to send immediate commands.
Network Interface Commands
Table 33 on page 78 lists the network interface commands. Unless specifically
described otherwise, the commands in the table apply to Layer 5 network
interfaces only.
The command names listed in the table are suggestions; for the Layer 5 device
commands, they are defined in the OpenLDV Developer Example by the