MOV or RDLONG

T Chap

I am trying to understand the difference.

Are these the same?


MOV temp1, accel

RDLONG Temp1, accel

accel RES 1 'local to asm, Why are not local variables specified as long, word, byte etc. I assume you ONLY have longs in ASM.


So far I think that for Longs set in the Main program (the caller of the ASM method), you would pass the address of the long in main
to the method with a parameter. Then if that variable needs to be accessed, you RDLONG the pointer to acceess the 'outside world'. But if you are working with local
declared variables in the ASM object/method, you just mov them.

Post Edited (TChapman) : 8/17/2009 5:15:10 PM GMT

Mike Green

MOV moves a 32-bit word from one cog location to another. "MOV temp,accel" moves the contents of "accel" to "temp", both cog locations.

RDLONG moves a 32-bit word from a hub memory location to a cog memory location. The source operand value specifies the hub address. In your case, "RDLONG temp,accel" takes the hub address contained in cog location "accel" and uses that to read a 32-bit long from hub memory into cog location "temp".

In ASM there are only 32-bit memory locations. You can pack 16-bit words and 8-bit bytes into these locations using the assembler, but there are no instructions to directly manipulate them. It's all 32-bit values.

T Chap

Thanks Mike. It is a bit confusing to me, in Spin you just have variables. You set the variable to whatever you want, read them as needed.

A real world scenario, are these the same?

PUB  moveX
     motorr(0, @X, @Xcurrent, 1, 0, @Xdone)

PUB motorr( ipinstart, ipos, icurrent, iforward, ireverse, iID )
  [noparse][[/noparse]  ... ]
  newposition := ipos
  currentposition := icurrent
  return COGNEW( @cogstart, @ipinstart )   


DAT
                    ORG     0
cogstart
                    JMP     #cogstart0
pinstart         LONG    0               ' input parameters
radr              LONG    0
forward         LONG    0
reverse         LONG    0
ID                LONG    0
cogstart0                                 


[noparse][[/noparse] ... ]    skipping code

repeat1
                'if  LONG[noparse][[/noparse]newposition] < LONG[noparse][[/noparse]currentposition]   
                RDLONG  ctmp1, newposition            
                MOV     ctmp2, currentposition          
                RDLONG  ctmp2, ctmp2          
                CMPS    ctmp1, ctmp2    WC        'if newpos < current, set C flag to 1
    IF_C   JMP     #endif2                'jmp to #endif2 (if c flag is 1) 
                MOV     rep3cnt, C1000     

'versus

repeat1
             CMPS    newposition, currentposition    WC    'if newpos < current, set C flag to 1
 IF_C   JMP     #endif2         ' jmp to #endif2 (if c flag is 1) 

ctmp1           RES     1               ' PASM variables
ctmp2           RES     1 
run               RES     1  

Post Edited (TChapman) : 8/17/2009 5:49:36 PM GMT

T Chap

I just tested the alternative short version above and it worked fine what what I can tell. Seems you can do CMPS on global variables just like locals.

henry99

I'm not a super expert at asm but:
RDLONG ctmp1, newposition
MOV ctmp2, currentposition
RDLONG ctmp2, ctmp2
CMPS ctmp1, ctmp2

Why don't you just write
RDLONG ctmp1, newposition
RDLONG ctmp2, currentposition
CMPS ctmp1, ctmp2

Also this statement:
CMPS newposition, currentposition WC

Will compare only the pointer locations and not the values from Hub memory.

T Chap

OK I got it. You always first read the values from the locations via pointers into temp local variable and then do your processes.

RDLONG temp1, pointer1 'get the values into local vars
RDLONG temp2, pointer2 'get the values
CMPS temp1, temp2 compare

mpark

Also, it'll probably help if you stop thinking in terms of local vs. global variables ('cause that's not the difference here) and focus on cog vs. hub memory.