-- HOME --


MSW Logo Primitives 

The syntax for 'calling' the mswbrick DLLs is quite involved. Typically, users must deal with long and complex commands along the lines of: dllcall [v TurnPortOn v 0]. The likelihood of errors is quite high. The calls are further complicated by the importance of 'case'. "TurnPortOn", for example, is not the same as "TurnportOn". 

MSW Logo will report a "Function not found." error unless the case matches exactly. These precise requirements can cause frustration when errors are made.

The alternative is to define the calls as MSW Logo "primitives" which provide much simpler calls for the user. These new primitives load automatically when MSW Logo loads and are available in exactly the same way that 'native' commands such as "forward" and "clearscreen" are used. As far as the user is concerned, your new primitives are an integral part of MSW Logo.

Defining New Primitives

To define a new primitive you must write a procedure containing the commands and then save the procedure into the MSW Logo "logolib" directory. The name of the procedure must be the same as the name of the file. The filename has no 'extension'. If you add the usual ".lgo" extension your primitive will not work.

For example …

Before you start using MSW Logo to control the Brick you must load the mswbrick DLL and then 'turn on' the tower. This requires two separate commands:

   dllload "mswbrick.dll
   dllcall[v TurnPortOn v 0]

The idea is to incorporate these commands into a new procedure called "toweron" and save the procedure as a file called "toweron" into the logolib directory.

ie
to TowerOn
   dllload "mswbrick.dll
   dllcall[v TurnPortOn v 0]
end 

When MSW Logo starts up it will automatically load your file and make the procedure available as a new primitive. The user simply types "toweron" (without the quotes) in the MSW Logo command line and the instructions within the file toweron are carried out.

The same process is used to create single files containing each of the sets of commands you want to define as new "primitives".

The full set of sample mswbrick primitives is listed on the following pages …

NOTE: MSW Logo is not fussy about capitals, but the DLLCALL commands must contain correct capitalisation or you will get a "Function not found." Error message.

MSWBRICK Primitives

Tower Setup

to TowerOn 
   dllload "mswbrick.dll 
   dllcall[v TurnPortOn v 0]
end 

to TowerOff 
   dllcall[v TurnPortOff v 0] 
   dllfree
end


Motor Control

to MotorAOn 
   dllcall[v MotorAOn v 0]
end

to MotorAOff 
   dllcall[v MotorAOff v 0]
end

to MotorAForward 
   dllcall[v MotorAForward v 0]
end

to MotorAReverse 
   dllcall[v MotorAReverse v 0]
end

to MotorBOn 
   dllcall[v MotorBOn v 0]
end

to MotorBOff 
   dllcall[v MotorBOff v 0]
end

to MotorBForward 
   dllcall[v MotorBForward v 0]
end

to MotorBReverse 
   dllcall[v MotorBReverse v 0]
end 

to MotorCOn 
   dllcall[v MotorCOn v 0]
end

to MotorCOff 
dllcall[v MotorCOff v 0]
end

to MotorCForward 
   dllcall[v MotorCForward v 0]
end

to MotorCReverse 
   dllcall[v MotorCReverse v 0]
end


Sensor Control

to Sensor1On 
   dllcall [v Sensor1On v 0]
end 

to Sensor1 
   make "Sensor1Value dllcall [w Sensor1Value v 0]
end

to Sensor1Off 
   dllcall [v Sensor1Off v 0]
end

to Sensor2On 
   dllcall [v Sensor2On v 0]
end

to Sensor2 
   make "Sensor2Value dllcall [w Sensor2Value v 0]
end

to Sensor2Off 
   dllcall [v Sensor2Off v 0]
end

to Sensor3On 
   dllcall [v Sensor3On v 0]
end

to Sensor3 
   make "Sensor3Value dllcall [w Sensor3Value v 0]
end

to Sensor3Off 
   dllcall [v Sensor3Off v 0]
end


NOTE: Each new primitive is saved as a separate file. The set listed above was saved as 23 individual files, each with the same filename as the name for the procedure (in the "to" line). You can't collect all of your procedures together and save them as one file.


Logo Primitives versus DLL Calls

Compare the following …

Using MSW Logo Primitive Commands  Using DLLCALL
TowerOn
wait 30 ; (See NOTE below.)
MotorAForward
MotorAOn
wait 120
MotorAOff
TowerOff		 dllload "mswbrick.dll 
dllcall[v TurnPortOn v 0]
wait 30
dllcall[v MotorAForward v 0]
dllcall[v MotorAOn v 0]
wait 120
dllcall[v MotorAOff v 0]
dllcall[v TurnPortOff v 0]
dllfree

NOTE: The "wait 30" command in the second line allows a delay while the tower is initialising. If you don't allow a small delay before calling another command your system may hang.

Both sets of code will turn on MotorA for two seconds and then turn it off again. It should be obvious which set of commands is easiest to understand and use.

Your new primitive commands can be used in procedures in the same way as all other MSW Logo commands. A typical procedure to make the RCX brick move forward, spin and then stop would be …

to travel
   TowerOn
   wait 30
   ; Waits for the Tower to turn on
   MotorAForward
   MotorBForward
   MotorAOn
   MotorBOn
   wait 120
   ; Buggy moves forward
   MotorAReverse
   wait 120
   ; Buggy spins. (MotorB is still Forward.)
   MotorAOff
   MotorBOff
   TowerOff
end