problem w/ mov :x,cnt

janb · 2007-09-11 02:57

·Hi,
I spent already few days to debug this problem, wrote from scratch special test code and
at the end decided to ask for help. There is sth fundamentally wrong w/ my assembler code.

The grand scheme looks as follows:
cog0 runs SPIN code + TV driver. It owns 3 arrays & 1 semaphore-like variable 'myStat'

 long iBuf[noparse][[/noparse]iBLen] '  ASM input buf         
 long oBuf[noparse][[/noparse]oBLen] '  ASM output buf
 long dataAr[noparse][[/noparse]arLen] '  I/O data array
 long myStat 'status of control, LOCK-protected

cog0 passes iBuf[noparse]/noparse to ASM code running on cog1

The goal· of cog1 is to wait until myStat==1, then fill internal cog1 array with some series of values and export it back to the Hub array to the address dataAr[noparse]/noparse.

Next cog0· does some QA on the dataAr[noparse]/noparse, clears it, resets myStat to 1 and all repeats.
This scheme works very good under one condition:

I can't use

mov :bhla, cnt

in the assembler loop filling internal cog1 array. The code of this ASM function is below. Full code is attached - (hook up TV to pins 12,..., LED on pin16 will show the ASM code is working)

FillCogArray { in COG }
        mov :val,#20                   
        movd  :self, #cogArr 'set initial address
        mov   :i, #cogArrLen ' set size of array
:self   mov  0-0, :val   'store some default value 
        add   :self, :d_inc  'incr destination in instruction above
        'mov :val,cnt     'BREAKS ~1/1000
        add     :val,#20  'WORKS  always
        nop
        djnz  :i, #:self   'go to next element
:i long 0
:val long 0

:d_inc LONG  $0000_0200
FillCogArray_ret ret

If I choose to fill ASM array with values incremented by 20 all works (as in the example above), even for 1000 events (cycles of calling ASM code)
But if I simply· swap 2 active lines·to

        mov :val,cnt     'BREAKS ~1/1000
        'add     :val,#20  'WORKS  always

·propeller· becomes unstable.
It always runs in to some trouble after _many_ events:
- most often it works fine for 50-80 events and suddenly the values in output array seen by cog0 are wrong (increment between values is not 20 - I abort cog0 in such case)
- sometimes ASM code stays forever in the FillCogArray procedure - I see it because myStat seen by cog0 is 2 and LED on pin 16 still blinks
- sometimes TV display disappears - meaning sth wrong happens to pins12,....
- never the same problem will happen twice in the row

The bottom line is ASM code gets sick if I try to access very often clock counter .
Has any one seen problem like this?
Is there sth obviously wrong in my code?
Hope it is sth trivial
Jan··

Post Edited (janb) : 9/11/2007 3:15:16 AM GMT

deSilva · 2007-09-11 06:13

You shouldn't put variables in between your code! Before you reach RET there are three obstacles for the poor program

In most cases they wil be NOPs, but when in comes to CNT very funny opcodes might occur

So you have to skip the fancy ":" stuff and use "global" names... no other chance...
Or you "jump over" the variables...

janb · 2007-09-12 01:22

Hi deSilva,
that was it. If I think back how many hours I have invested to isolate this problem!
Thank you very much for this 2 lines of deep insight.
I wish this warning would be part of the Parallax official writeup in the Assembler section.
Jan

problem w/ mov :x,cnt

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