DAP Technology 1394, Operation Manual

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Mil1394 Protocol support
267 Copyright © DapTechnology B.V., 2005-2019 - All Rights Reserved., 5/20/2019
Each signal is in fact a field within a packet, the ASM packet. Each signal is therefore to be interpreted
from a certain number of bits, at a certain offset from the start of the packet; in number of 32 bit blocks
called quadlets and possibly a number of additional, individual bits.
It is also linked to a channel and message ID; these are fields from the header of the packet. Their value
selects which signal values may be expected to be contained in the packet's payload data, at their
respective offsets. The bit values may also be interpreted as being signed or not, floating point or integer,
and their value may be linked to an enumeration of strings.
This information can be embedded in the XML file as shown below:
<!-- Message Definitions -->
< MessageDefinitions >
< MessageDefinition Channel ="4" MessageID ="6000004" PacketSize ="320">
< SignalGroup >
< Signal Name ="engine1_heartbeat" DataType ="udec" QuadOffset ="0"/>
< Signal Name ="engine1_pressure" DataType ="float" QuadOffset ="1"
Factor ="2.5" Offset ="-1.5" MinValue ="-50" MaxValue ="99.5"
Units ="bar"/>
</ SignalGroup >
< Signal Name ="engine1_temperature" DataType ="dec" QuadOffset ="2"
FirstBit ="16" NumBits ="16"/>
</ MessageDefinition >
< MessageDefinition Channel ="5" MessageID ="0">
< SignalGroup >
< Signal Name ="sensors_heartbeat" DataType ="udec" QuadOffset ="0"/>
< Signal Name ="sensors_sensor1" DataType ="dec" QuadOffset ="2"
EnumName ="switch"/>
</ SignalGroup >
</ MessageDefinition >
</ MessageDefinitions >
The XML settings file was introduced to allow you to automatically import signal definitions from an
existing database, since this format is relatively easy to generate and understand. You may generate
multiple files for different usages and security levels. Undefined signals will simply be shown as such,
although the values themselves will still be accessible. For instance, the same recording file may show
different levels of detail on several computers; each set up with a different Mil1394 XML settings file.
Enumeration strings
The example above contains a signal called "sensors_sensor1", which (for the sake of illustration) refers
to the "switch" enumeration. This enumeration, defined below, links the value 0 to "off", 1 to "on", and any
value between 2 and 255 (inclusive) to "unspecified". The application uses this hint on several places to
translate the signal's value to the corresponding string (using a drop down box), and vice versa.
<!-- String Representations -->
< Enums >
< Enum Name ="switch">
< Item Value ="0" Label ="off"/>
< Item Value ="1" Label ="on"/>
< Range Start ="2" End ="255" Label ="unspecified"/>
</ Enum >
</ Enums >
13.5.3. Packet Formats
Besides being able to specify the signal data payload of the ASM message packet, it is also possible to
specify how its header and trailer are to be interpreted. And which signals should be included by default,
regardless of the channel and message ID. Similarly, the STOF packet can be precisely specified. The
syntax of the field definitions is similar to the signal definitions. See the
Mil1394 Settings File Format for
more information.
<!-- Packet Formats -->
< ASMPacketFormat >
< ASMHeader >
< MessageID QuadOffset ="0" FirstBit ="0" NumBits ="32"
DataType ="udec">
< DecimalParts >
< Branch NumDigits ="2"/>
< Channel NumDigits ="2"/>
< Message NumDigits ="6"/>