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Participant
1,342 Views
Registered: ‎07-30-2017

## 35*35 mutiplier sequential_pipe with one or two register(A,B)

Dear all,

Can 35*35 mutiplier be realized in sequential mode （one dsp in dynamic opmode）with the attribute of AREG\BREG （1 or 2 ）？I have realized without registers.But when AREG\BREG is set to 1 or 2, The problem arises.

Supposing that the result needs two posedges to produce,but the opmode changes on the second posedge Is there any effect to the result?

thank you !

2 Replies
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Guide
1,312 Views
Registered: ‎01-23-2009

It is hard to understand what you are asking...

A 35x35 multiplier cannot be implemented completely in a single DSP48. The primary reason for this is that there simply aren't enough bits in the accumulator (P) register; the maximum size of a 35x35 multiplication is 70 bits, which is larger than the P register size of 48 bits.

Furthermore, you cannot do a 35x35 multiplication with one DSP using 2 clocks - it needs (I think) a minimum of 4. The individual multiplication is 25x18, so each multiplicand will need to be split up into two groups such that each partial multiplicand is smaller than 25 or 18, call them AH and AL and BH and BL. You then need to multiply AL*BL,, AL*BH, AH*BL, and BH*BL. These partial products then need to be added together with appropriate shift values.

Avrum

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Voyager
1,310 Views
Registered: ‎06-24-2013

Hey @sastliuwei,

Can 35*35 mutiplier be realized in sequential mode (single DSP)?

I haven't tried yet, but my gut feeling tells me that it should be doable.

I have realized without registers.But when AREG\BREG is set to 1 or 2, The problem arises.

What exactly is the problem you are seeing with pipelining registers?

Supposing that the result needs two posedges to produce,but the opmode changes on the second posedge Is there any effect to the result?

If I remember correctly, the DSP48 block always produces a result on every clock cycle, so changing the opmode on every cycle is fine as well and yes, it will affect the result.

Best,

Herbert

-------------- Yes, I do this for fun!