PASM MOV to Array Question

Pascal22

hi,

how to make something like this in PASM : (write a value in an array)

MOV TmpVal, Adr_2_Array
ADD TmpVal, Offset
MOV TmpVal, Value

Adr_2_Array contain the base adresse of an array localised in the cog memory
Offset contain a position in the array

the last line do not work : the value is moved in the TmpVal register and not in the (adresse_of_array+offset) register


sorry for my poor english...:shakehead:

Mike Green

You actually have to modify the instruction itself like this:

movd  copyInst, #addressOfArray ' initialize to address of array
           shl   offset, #9 ' position offset to destination field bits
           add   copyInst, offset ' add modified offset to instruction
           shr   offset, #9 ' delay required here, might as well correct offset
copyInst   mov   0-0, valueToCopy ' copy value, "0-0" is just a placeholder

Note that you need a one instruction delay between the last change to the
instruction and when it's executed. The 2nd SHR serves as the delay and it
repositions the offset back to where it was originally. You could use any other
single instruction (like a NOP) for the same purpose.

The "0-0" is just a placeholder to show you which fields of which instructions are
calculated at run time. You could use just "0" if you want, but "0-0" can be more
meaningful.

Pascal22

thank's for the response.

I unterstand that must have 4 instructions between the movd and the modified instustion (4 cycles of decoding by instruction)... that's right ?

Another question :

the cog's memory is long aligned, so the offset's step is 1 vs hub's memory who the offset's step is 4 (for a long value) ?

jazzed

Pascal22 wrote: »

I unterstand that must have 4 instructions between the movd and the modified instustion (4 cycles of decoding by instruction)... that's right ?

Only one instruction is necessary between movd,movs,movi and the modified instruction.

Pascal22 wrote: »

the cog's memory is long aligned, so the offset's step is 1 vs hub's memory who the offset's step is 4 (for a long value) ?

Yep you got it.

Mike Green

Remember that the ADD instruction also changes the MOV instruction and the one instruction delay is from the ADD to the MOV.