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Kevin Brown
Guest
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 Posted:
Fri Dec 10, 2004 5:18 am Post subject:
What is the purpose of the 2 registers on A and B in the V4 |
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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 |
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Philip Freidin
Guest
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| Posted:
Sat Dec 11, 2004 3:20 am Post subject:
Re: What is the purpose of the 2 registers on A and B in the |
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On 9 Dec 2004 16:18:39 -0800, "Kevin Brown" <kbrown_home@hotmail.com> wrote:
| Quote: | 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
|
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 |
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Vic Vadi
Guest
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| Posted:
Tue Dec 14, 2004 12:53 am Post subject:
Re: What is the purpose of the 2 registers on A and B in the |
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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 Freidin wrote:
| Quote: | On 9 Dec 2004 16:18:39 -0800, "Kevin Brown" <kbrown_home@hotmail.com> wrote:
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
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 |
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Vic Vadi
Guest
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| Posted:
Tue Dec 14, 2004 12:57 am Post subject:
Re: What is the purpose of the 2 registers on A and B in the |
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Vic Vadi wrote:
| Quote: | 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.
|
Correction - I meant to say Larger input adders
such as adding more than three numbers together in
multiple DSP48's.
- Vic |
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