What is the purpose of the 2 registers on A and B in the V4 Extreme DSP?

In the extreme DSP slice there are two registers before the multiplication on each of the A and B inputs. Does anyone know why you would need 2 registers before the multiplication?

At first I thought it may be a register similar to the one in a MULT18x18s, but changing the number of registers on A and B from 1 to 2 had no effect on timing. Also it wouldn't make sense since A and B are individually selectable to have 0,1, or 2 registers.

-Kevin

Reply to
Kevin Brown
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If you are doing larger multiplies (36x18, 36x36) you may need to delay partial operands so that all the pieces arrive at the destination at the same time.

For IIR filters, you may not be able to tollerate multiple pipe stages, so that may be a use for the "0 registers"

Philip Freidin Fliptronics

Reply to
Philip Freidin

Philip is correct but there are tons of other applications.

In Systolic Filters(Direct Form with extra pipelining), Direct Form Filters, Complex Multiplies etc. - the second A and B Register is extremely useful. Its also useful if you are building Larger adders and multipliers out of multiple DSP48's.

In fact using the internal cascades and the dual registers - you can place an N-tap Systolic filter running at Max Speed in a column of N DSP48's and only need to enter with your input data at the bottom most DSP48 and exit with your output from the top most DSP48!

- Vic

Philip Freid> > >In the extreme DSP slice there are two registers before the

Reply to
Vic Vadi

Correction - I meant to say Larger input adders such as adding more than three numbers together in multiple DSP48's.

- Vic

Reply to
Vic Vadi

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