Lookup tables in VAR blocks?

Jack Buffington · 2010-04-02 18:33

I tacked this onto a previous topic but that topic was a little old and didn't get any replies...

Does anyone know how to initialize an array in a VAR block with pre-defined values. I need to pass the address of the lookup table to an assembly program. The lookup table will be followed by other variables that the assembly will need to reference. I can create a lookup table in a DAT block and then reference it from SPIN like this but that won't work for me directly.

DAT

lookupTable long        1,2,3,4,5,6,7,8,9,10

PUB start

  dira := $FFFFFFFF
  repeat
     outa := lookupTable

I could do something like this but it sucks up another chunk of HUB RAM the same size as the lookup table. I'm tight on HUB RAM so I would prefer to not do that.

DAT
lookupTable long        1,2,3,4,5,6,7,8,9,10

VAR
long    theTable[noparse][[/noparse]10]
long    count
  
PUB start

  repeat count from 0 to 9
    theTable[noparse][[/noparse]count] := lookupTable[noparse][[/noparse]count]

  cognew(@PmyAssemblyStart,@theTable[noparse][[/noparse]0])

Is there some way to just initialize an array from within the VAR block. I'm not seeing anything in the propeller manual.

Phil Pilgrim (PhiPi) · 2010-04-02 19:06

You can pass the hub address of a DAT block to an assembly cog the same as you do a VAR array. For your "other variables" that you need to pass, just tack them onto the end of the DAT block, initialized to zeroes, instead of declaring them as VARs.

-Phil

Dave Hein · 2010-04-02 20:45

If you are providing a list of variables to the the assembly routine you can just add the address of the DAT table to the variable list.· Something like this:

DAT
lookupTable long        1,2,3,4,5,6,7,8,9,10 
 
VAR
long    varlist[noparse][[/noparse]3]
  
PUB start(arg1, arg2) 
  varlist[noparse][[/noparse]0] := arg1
  varlist[noparse][[/noparse]1] := arg2
  varlist[noparse][[/noparse]2] := @lookupTable
  cognew(@PmyAssemblyStart,@varlist)

mpark · 2010-04-02 21:00

Your other post did get replies. Did you even look?

Jack Buffington · 2010-04-02 21:30

Got it! Thanks!

One gotcha that I found was that the compiler seems to join multiple DAT sections into one address space so if I declare my variables in one file, I have to put my program in another file, which is what I normally do but for the sake of testing things out, I didn't.

For those of you searching for this same thing, here is the code that I wrote and tested:

In one file:

OBJ
        DISPLAY : "lookup02.spin"  
DAT
temp3         long      0                       ' this is here to keep things long aligned
lookupTable   long      1,2,3,4,5,6,7,8,9,10
otherVariable long      0
anotherTable  long      $FF[noparse][[/noparse]600]                ' create a table 

PUB start

  
  otherVariable := 37
  anotherTable[noparse][[/noparse]99] := 16
  anotherTable[noparse][[/noparse]100] := 17
  anotherTable[noparse][[/noparse]101] := 18
  DISPLAY.Start(@lookupTable[noparse][[/noparse]0])

In the other file:

PUB Start  (address)
  cognew(@startDisplay,address)

DAT

startDisplay  mov       dira,#255
              mov       temp,par
              add       temp,#40                ' skip over the 10 lookupTable variables
              add       temp,#4                 ' skip over otherVariable
              add       temp,#400               ' skip over 100 variables in anotherTable
              rdbyte    temp2,temp
              mov       outa,temp2            ' output shows 17

AA            jmp       #AA
temp    long  0
temp2   long  0

Post Edited (Jack Buffington) : 4/2/2010 9:36:37 PM GMT

Jack Buffington · 2010-04-02 21:36

mpark,

I didn't see any e-mail notice from the forum so I posted again. In looking back now, I see that it was there after all. Sorry for the repost and thanks for your reply on the other thread.

Phil Pilgrim (PhiPi) · 2010-04-02 21:44

You can reset the cog address pointer using the ORG statement. That way each distinct block of assembly code in a DAT section has its own start address, viz:

DAT
[s]temp3         long      0                       ' this is here to keep things long aligned[/s] NOT NECESSARY
lookupTable   long      1,2,3,4,5,6,7,8,9,10
otherVariable long      0
anotherTable  long      $FF[noparse][[/noparse]600]                ' create a table 

PUB start  
  otherVariable := 37
  anotherTable[noparse][[/noparse]99] := 16
  anotherTable[noparse][[/noparse]100] := 17
  anotherTable[noparse][[/noparse]101] := 18
  cognew(@startDisplay,@lookupTable)

DAT
              [b]org       0[/b]

startDisplay  mov       dira,#255
              mov       temp,par
              add       temp,#40                ' skip over the 10 lookupTable variables
              add       temp,#4                 ' skip over otherVariable
              add       temp,#400               ' skip over 100 variables in anotherTable
              rdbyte    temp2,temp
              mov       outa,temp2            ' output shows 17

AA            jmp       #AA
temp    long  0
temp2   long  0

-Phil

Lookup tables in VAR blocks?

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