Database Definition

The database for FIX Gateway is configured using a colon ':' delimited text file. The database is initialized based on the contents of this file before any of the plugins are loaded. The database is immutable. It cannot be changed by plugins once the program is loaded. Users can modify the database definition for their own use. ##File Format The following is an excerpt from the default database definition file.

e=2:Engines
c=4:Cylinders per engine
t=2:Fuel Tanks
b=16:Generic Buttons
r=4:Generic Encoders
a=16:Generic Analog
---
#Key:Description:Type:Min:Max:Units:Initial:TOL:Auxiliary Data
ANLGa:Generic Analog %a:float:0:1:%/100:0.0:2000:
BTNb:Generic Button %b:bool:0:1::False:0:
ENCr:Generic Encoder %r:int:-32768:32767:Pulses:0:0:
IAS:Indicated Airspeed:float:0:1000:knots:0.0:2000:Min,Max,V1,V2,Vne,Vfe,Vmc,Va,Vno,Vs,Vs0,Vx,Vy
ALT:Indicated Altitude:float:-1000:60000:ft:0.0:2000:
BARO:Altimeter Setting:float:0:35:inHg:29.92:2000:
VS:Vertical Speed:float:-10000:10000:ft/min:0.0:2000:Min,Max,lowWarn,highWarn,lowAlarm,highAlarm
HEAD:Current Aircraft Magnetic Heading:float:0:360:deg:0.0:2000:
AOA:Angle of attack:float:-180:180:deg:0.0:200:Min,Max,0g,Warn,Stall
CTLPTCH:Pitch Control:float:-1:1:%/100:0.0:200:
CTLROLL:Roll Control:float:-1:1:%/100:0.0:200:
THRe:Throttle Control Engine %e:float:0:1:%/100:0.0:1000:
OILPe:Oil Pressure Engine %e:float:0:200:psi:0.0:2000:Min,Max,lowWarn,highWarn,lowAlarm,highAlarm
MAPe:Manifold Pressure Engine %e:float:0:60:inHg:0.0:2000:
EGTec:Exhaust Gas Temp Engine %e, Cylinder %c:float:0:1000:degC:0.0:2000:
CHTec:Cylinder Head Temp Engine %e, Cylinder %c:float:0:1000:degC:0.0:2000:
FUELQt:Fuel Quantity Tank %t:float:0:200:gal:0.0:2000:Min,Max,lowWarn,lowAlarm
TACHe:Engine RPM:int:0:10000:RPM:0:2000:Min,Max,lowWarn,highWarn,lowAlarm,highAlarm
LAT:Latitude:float:-90:90:deg:0.0:2000:
LONG:Longitude:float:-180:180:deg:0:2000:

The first few lines describe variables. Variables are a way to eliminate duplication in the database definition file. The line that begins with '---' tells FIXGateway that the variable definitions are finished and to treat the rest of the file as item definitions. Any line that begins with a # is treated as a comment.

#Variables Each variable when found in the definition will cause the initialization routine to duplicate and index that particular datapoint based on the number given. For example the variable e=2 represents the number of engines that our aircraft will have. Instead of having to write each of the following three points twice (once for each engine) we just use the lower case letter 'e' in the Key definition and %e in the description.

THRe:Throttle Control Engine %e:float:0:1:%/100:0.0:1000:
OILPe:Oil Pressure Engine %e:float:0:200:psi:0.0:2000:Min,Max,lowWarn,highWarn,lowAlarm,highAlarm
MAPe:Manifold Pressure Engine %e:float:0:60:inHg:0.0:2000:

This would cause THR1 and THR2 to be created in the database. This doesn't seem like much with just this example but consider the following...

EGTec:Exhaust Gas Temp Engine %e, Cylinder %c:float:0:1000:degC:0.0:2000:

...if e=2 and c=6 that's a single line that would produce 12 items in the database. It also makes it quite easy for a user to change the counts of these things without having to search the entire database file to manage the data points. There are a number of items that use the 'e' for number of engine. Each of these would have to be managed individually if we had a line for each point. As it is the user simply changes the line e=1 to e=2 if the aircraft only has two engines, and he'll get two Oil Pressures, Two Manifold Pressures, two Fuel Flows etc.

#Database Item Definitions

The lines that follow the '---' are definitions of the individual database items. The format is...

Key:Description:Type:Min:Max:Units:Initial:TOL:Auxiliary Data

###Key The Key is the unique identifier of the data point. The key should be in all capitol letters as any lower case letter will be considered to be a variable. ###Description The description is obvious. It is the human readable name of the item. '%x' can be used in the description to cause variable duplication and indexing. The text "Oil Pressure Engine #%e" would become "Oil Pressure Engine #1" during the fist item's creation and "Oil Pressure Engine #2" during the second. ###Type There are four datatypes recognized by FIX Gateway, float, int, bool and str. float is the most common and simply represents a real number. int represents a whole number, or a number that has no decimal point. These are good for counters or numbers that would never contain a fractional part. bool is boolean value or a True/False value. Buttons and switches would be the most common booleans. str is a text string. This might be the aircrafts registration number or the time in string format. ###Min and Max These are the absolute limits by which the item's value will be constrained. Regardless of what value is written to the database the database item will never exceed these values. For example the magnetic heading (HEAD) has a Min of 0 and a Max of 360. If 370 is written to the point the actual value stored in the database would be 360. ###Units These are the engineering units applied to the item. "psi", "inHg", "feet", or "knots" are examples of units. ###Initial This is the initial value that the item will contain on start up. Most would be zero but occasionally it makes sense to initialize a datapoint to something else. For example the altimeter setting (BARO) is initialized to 29.92. ###TOL TOL stands for Time Out Lifetime in milliseconds. It's the amount of time that is given for each point to be written to the database. If a value is not written to the database in this amount of time the item is considered to be 'old' and the point will have the 'old' flag set to True when the value is read from the database. It is assumed that for the most part, the TOL is set to double the update rate. For some points a timeout does not make sense. If the TOL is set to zero the item will never be considered to be old. ###Auxiliary Data The Auxiliary Data (or Aux Data) is additional data that is associated with the point. It is mostly used for ranging instruments and indicating alarm and warning set points. It could be used for other things like 'V' speeds for Indicated airspeed as well. These aux data values are assumed to be of the same data type and should be within the same range as the item itself. They are simply stored in the database and delivered to the plugins that need them.

There are six fairly common aux data points, Min, Max, lowWarn, lowAlarm, highWarn and highAlarm. Min and Max here don't override the Min and Max above (probably should change the names to avoid confusion.) they would not affect the value that the database would store but are most often used to change the indicating range of the item. The other four might be used to indicate yellow arcs and/or red lines on gauges. In fact all of the gauges in pyEfis use these six values to determine the range of the gauge and the yellow and red arcs that are on the gauge. All a pyEfis gauge widget needs to know to do it's job is the key of the point you want to display. The aux data tells it everything else that it needs to know to do it's job.

The reason that the Auxiliary Data is stored in the FIX Gateway database instead of being handed off to the displaying device, is to make integration simpler. There may be several EFIS screens in the aircraft and each one would have to be configured with all of the low / warning setpoints for each point. Centralizing this information in the gateway makes it easier. It could also mean that a flap controller could have access to the Vfe data from the IAS point and then could protest in some way or indicate an alarm if the pilot tried to lower the flaps above this threshold. The flap controller would not have to be configured with this information it would simply be available and it would always match what is indicated on the Airspeed Indicator(s).