Array in Assembly Works Weird

Jamesx · 2007-02-04 16:28

Team:

I amtrying to sort out an array in assembly, using methods outlines awhile ago in thread
http://forums.parallax.com/forums/default.aspx?f=25&m=148004

I've gotten something to work, but it works only partially and in a fashion that I do not understand.

              'there is something wrong here.  I cannot find it.
              mov       t2,     #16            
Loop_16                                          
              mov       zz,     #LED_0-1
              add       zz,     t2              ' address of LED_0 - 1 in zz
              movs      yy16,   zz              ' address of LED_0 - 1 + t2 to yy16 source
yy16       mov       ShiftVal, 0-0             ' LED_0[noparse][[/noparse]t2] > ShiftVal'                                        
              shl       ShiftVal,#25            ' only lowest 7 bits to be shifted out
              mov       t3,     #7              ' t3 is number of bits to shift out'
              call      #shiftBits
              djnz      t2,     #Loop_16
'...

shiftBits  nop 
Bits        rol       ShiftVal,#1   wc        ' C flag set to Value's original bit 31.
              muxc      outa,   SIN             ' mux it into SIN pin, and pulse SCLK pin                                           
              or        outa,   SCLK            ' after Read, then cycle CLK High                                                     
              andn      outa,   SCLK            ' CLK Low
              djnz      t3,     #Bits           ' loop thru Bits 7 times
              andn      outa,   SIN             ' Leave SIN low at end of shiftout     
shiftBits_Ret ret

'...
LED_0         long      %00000000            
LED_1         long      %00000000         
LED_2         long      %00000000          
LED_3         long      %00000000           
LED_4         long      %00000000            
LED_5         long      %00000000           
LED_6         long      %00000000           
LED_7         long      %00000000             
LED_8         long      %00000000           
LED_9         long      %00000000            'this does not turn on LED
LED_10        long      %00001000            'this turns on LED
LED_11        long      %00000000            
LED_12        long      %00000000            
LED_13        long      %00000000            
LED_14        long      %00000000            
LED_15        long      %00000000

In the above code, the each LED_n indicates the power level of a different LED. These registers, 7 bits, are to be shifted out as to an LED driver chip (TLC5923) MSB first, starting with LED_15. There is an LED connected to a the 9 pin of the LED driver.

I would have thought the above code would adjust the LED on pin 10, but no. This code adjusts the LED on pin 9. There is something apparently something wrong somewhere but I am stumped. Any ideas would be appreciated.

Thanks,

Jim C

inservi · 2007-02-04 17:18

Hello,
I not yet started to learn the Propeller assembly but i think that you must declaring each element as byte and not as long or initialize 32 bits not 8 ?

Best regards,
dro

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
in medio virtus

Jamesx · 2007-02-04 18:38

dro

Thanks for the idea. But I don't think that's it. I am able to manage the 32 bit longs OK. It seems to be in the indirect addressing part (MOVS) of the first loop.

Jim C

Mike Green · 2007-02-04 18:40

You have to have at least one instruction between something that modifies an instruction and the instruction itself. Try inserting a NOP just before yy16.

Jamesx · 2007-02-04 19:15

Mike:

Ahh... It all becomes clear. It works now.

In the earlier thread mentioned, you had said "note there's a 1 instruction delay because the Propeller fetches instructions ahead of time." I couldn't figure out what you were talking about, as there is no mention of this being problem in the manual under MOVS. But after banking my head against the wall for an hour without success, and seeing it work with the silly NOP, it all makes sense.

Thanks!

Jim C

Array in Assembly Works Weird

Comments