Marshall,
Looks like we'll have to give some thought to whether bigEndian and LSBF can go together. We've had no actual examples of this until now. I will bring that up with the OGF DFDL Workgroup. But to deal with this today, these kinds of mixed bit order situations generally require use of the dfdl:inputValueCalc and dfdl:outputValueCalc properties. A simple example is here: https://github.com/rchampag/dfdl/blob/master/arinc429-label/localizer-deviation-label.dfdl.xsd This was for individual bits, but in your case they would be wider integers. For your 3 fields in the example I suggest you parse as 4 fields h_slot2LSBs - 20 bits h_slot1 - 12 bits h_slot3 - 20 bits h_slot2MSBs - 12 bits You would do this all bigEndian and mostSignificantBitFirst. The above would go into a hidden group so they wouldn't show up in the logical data. Then you would have 3 logical ordinary, not hidden elements slot1 dfdl:inputValueCalc='{ ../h_slot1 }' slot2 dfdl:inputValueCalc='{ ( ../h_slot2MSBs * dfdl:int('x80000' ) + ../h_slot2LSBs }' slot3 dfdl:inputValueCalc='{ ../h_slot3 }' dfdl:int('x80000') constructs a integer from a hex string, and I think that's the right value. Or maybe it's 'x100000'. You can also use math.pow function as in xs:int(math:pow(2, 19)) (you need to add this namespace to your xs:schema element xmlns:math='http://www.w3.org/2005/xpath-functions/math') The tricky part is that for unparsing you must invert this using dfdl:outputValueCalc. So the 4 hidden elements would be like this: h_slot2LSBs dfdl:outputValueCalc="{ ../slot2 mod dfdl:int('x80000') }" h_slot1 dfdl:outputValueCalc='{ ../slot1 }' h_slot3 dfdl:outputValueCalc='{ ../slot3 }' h_slot2MSBs dfdl:outputValueCalc="{ ../slot2 idiv dfdl:int('x80000') }" or something like that. My details here are probably off by 1 or something. DFDL's Xpath-like expression language has the operators +, -, *, div, idiv, mod, and the math.pow() function. Alas there's no shift nor a bit-wise & and | operator. Generally it is possible to figure out how to achieve what you want by way of mathematical operations. Also note: If you want Link16 specific support we have a channel for FOUO email support which is [email protected]. ...mike beckerle Tresys ________________________________ From: Marshall Miller <[email protected]> Sent: Thursday, January 11, 2018 2:34:46 PM To: [email protected] Subject: Help implementing schema for SISO-J Hello, I am trying to implement a schema to describe a LINK-16 message embedded within a DIS Signal PDU as described by SISO-STD-002 [1], paragraph 5.2.2.9 and table 5.2.3; commonly referred to as SISO-J. The problem is that fields are packed into 32 bit words with big endian byte order, and little endian bitfield order. It is currently an error to specify a byteOrder of bigEndian with a bitOrder of leastSignificantBitFirst. Also, I have not found a way to set word size; it appears that word size is implicitly set to the size of each field. Following is a simple example to demonstrate how fields need to be interpreted. It is just an example and does not represent any part of a SISO-J message. Data is comprised of 3 unsigned integer bitfields: slot1 is 12 bits slot2 is 32 bits slot3 is 20 bits Given an input with the following bytes in hex: 01 23 45 67 89 AB CD EF Parsed results need to be (in hex): slot1: 0567 slot2: DEF01234 slot3: 089ABC Explanation of results: Since the bitfields need to consume data in a leastSignificantBitFirst order, it is easier to represent the input in right-to-left order where bits are consumed starting at the right and moving toward the left. Since words are 4 bytes, and in big endian order, the lowest bit in the 4th byte is the first bit to be consumed. Reordering the input data and consuming data from right to left yields the correct field boundaries. 89 AB CD EF 01 23 45 67 parse fields right to left 05 06 07 08 01 02 03 04 input byte position slot1 consumes the right 3 nibbles, slot2 consumes the next 8 nibbles, and slot3 consumes the left 5 nibbles. Could you please let me know if there is a way to parse fields in this manner? Marshall Miller [1] https://www.sisostds.org/DesktopModules/Bring2mind/DMX/Download.aspx?Command=Core_Download&EntryId=43048&PortalId=0&TabId=105
