Slice equation in bitstream

hey,

in FPGA-Editor i can choose a slice and type in an equation for this
block.
i need information, where i can find this equation (truth table) in
the generated bitstream and how
they are arranged.

thanks for help

On 17 Aug., 13:22, lembke.ste...@googlemail.com wrote:
> hey,
>
> in FPGA-Editor i can choose a slice and type in an equation for this
> block.
> i need information, where i can find this equation (truth table) in
> the generated bitstream and how
> they are arranged.
>
> thanks for help

not available fully, need write your RE tools to gain this info

you can try generate LL file, but that file doesnt have all the needed
some need still heavy RE :(

Antti

i found the location in the bitstream, where 'result-column' can be
found. when i use all 4 variables in the function, i can find exact
these column of the truth table in the bitstream.

(A3*A1)+(A2*A4)
05 37 00 00 => 0000 0101 0011 0111 0000 0000 0000 0000    (is the
same, as in the truth table)

but when i use less than 4 variables, the bits are not in the right
order (but the number of 1's is correct)

(A1+A2)*A4
00 77 00 00 => 0000 0000 0111 0111 0000 0000 0000 0000   (in other
order)

or

A1*A3:
05 05 00 00 => 0000 0101 0000 0101 0000 0000 0000 0000

<lembke.stefan@googlemail.com> wrote in message 
news:1187349760.044999.83000@19g2000hsx.googlegroups.com...
> hey,
>
> in FPGA-Editor i can choose a slice and type in an equation for this
> block.
> i need information, where i can find this equation (truth table) in
> the generated bitstream and how
> they are arranged.
>
> thanks for help
>
Hey backatyou,

I first did this 20 years ago with Xilinx parts. I guess the method hasn't 
changed.

1) Make a design.
2) Generate bitstream.
3) Edit function generator in XACT, sorry, FPGA editor.
4) Generate bitstream.
5) See what's changed from 2).

Not exactly rocket science, but effective nonetheless. You'll find the 
CLBs/Slices distributed regularly throughout the bitstream, I bet.

HTH., Syms. 

yes, that's the way i go.
but don't understand, why the order changes, when i use less than 4
variables ....

On 17 Aug., 14:28, lembke.ste...@googlemail.com wrote:
> i found the location in the bitstream, where 'result-column' can be
> found. when i use all 4 variables in the function, i can find exact
> these column of the truth table in the bitstream.
>
> (A3*A1)+(A2*A4)
> 05 37 00 00 => 0000 0101 0011 0111 0000 0000 0000 0000    (is the
> same, as in the truth table)
>
> but when i use less than 4 variables, the bits are not in the right
> order (but the number of 1's is correct)
>
> (A1+A2)*A4
> 00 77 00 00 => 0000 0000 0111 0111 0000 0000 0000 0000   (in other
> order)
>
> or
>
> A1*A3:
> 05 05 00 00 => 0000 0101 0000 0101 0000 0000 0000 0000

the LUT inputs are swapped randomly duting PR so that explains why the
appear in different places
think there are some settings to free LUT inputs but that may not
always work

Antti

<lembke.stefan@googlemail.com> wrote in message 
news:1187353683.189676.87220@k79g2000hse.googlegroups.com...
>i found the location in the bitstream, where 'result-column' can be
> found. when i use all 4 variables in the function, i can find exact
> these column of the truth table in the bitstream.
>
> (A3*A1)+(A2*A4)
> 05 37 00 00 => 0000 0101 0011 0111 0000 0000 0000 0000    (is the
> same, as in the truth table)
>
> but when i use less than 4 variables, the bits are not in the right
> order (but the number of 1's is correct)
>
> (A1+A2)*A4
> 00 77 00 00 => 0000 0000 0111 0111 0000 0000 0000 0000   (in other
> order)
>
> or
>
> A1*A3:
> 05 05 00 00 => 0000 0101 0000 0101 0000 0000 0000 0000
>
So, firstly, there only 16 bits in the LUT, right. You've written 16. So, 
let's look at just the first 16 bits of your truth table. In the second 
example, the A3 bit is 'don't care' so the equation implemented is :-
((A1+A2)*A4 * A3) + ((A1+A2)*A4 * ~A3)

HTH., Syms.

"Symon" <symon_brewer@hotmail.com> wrote in message 
news:fa44vo$dfg$1@aioe.org...
>>
> So, firstly, there only 16 bits in the LUT, right? You've written 32. So,
Whoops, correction above! 

yes, 16 bits, i know. but the tip with the don't cares is great.
thanks

hmm,  but that doesn't explain why the bits have a different position.
or i don't understand.