DK-DEV-4SGX230N Altera, DK-DEV-4SGX230N Datasheet - Page 50

• Manufacturer Part Number: DK-DEV-4SGX230N
• Description: KIT DEVELOPMENT STRATIX IV
• Manufacturer: Altera
• Series: Stratix® IVr
• Type: FPGAr

Specifications of DK-DEV-4SGX230N

• Contents: Development Board, Universal Power Supply, Cables and Software
• Silicon Manufacturer: Altera
• Core Architecture: FPGA
• Core Sub-architecture: Stratix
• Silicon Core Number: EP4S
• Silicon Family Name: Stratix IV GX
• Rohs Compliant: Yes
• For Use With/related Products: EP4SGX230K
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 544-2594

2–14
Figure 2–11. ALM in Shared Arithmetic Mode
Stratix IV Device Handbook Volume 1
datae0
datae1
datab
dataa
datad
datac
Shared Arithmetic Mode
In shared arithmetic mode, the ALM can implement a three-input add within the
ALM. In this mode, the ALM is configured with 4 four-input LUTs. Each LUT either
computes the sum of three inputs or the carry of three inputs. The output of the carry
computation is fed to the next adder (either to adder1 in the same ALM or to adder0 of
the next ALM in the LAB) using a dedicated connection called the shared arithmetic
chain. This shared arithmetic chain can significantly improve the performance of an
adder tree by reducing the number of summation stages required to implement an
adder tree.
You can find adder trees in many different applications. For example, the summation
of the partial products in a logic-based multiplier can be implemented in a tree
structure. Another example is a correlator function that can use a large adder tree to
sum filtered data samples in a given time frame to recover or de-spread data that was
transmitted using spread-spectrum technology.
Shared Arithmetic Chain
The shared arithmetic chain available in enhanced arithmetic mode allows the ALM
to implement a three-input add. This significantly reduces the resources necessary to
implement large adder trees or correlator functions.
Shared arithmetic chains can begin in either the first or sixth ALM in the LAB. The
Quartus II Compiler creates shared arithmetic chains longer than 20 (10 ALMs in
arithmetic or shared arithmetic mode) by linking LABs together automatically. For
enhanced fitting, a long shared arithmetic chain runs vertically, allowing fast
horizontal connections to the TriMatrix memory and DSP blocks. A shared arithmetic
chain can continue as far as a full column.
Figure 2–11
4-Input
4-Input
4-Input
4-Input
LUT
LUT
LUT
LUT
shared_arith_out
shows the ALM using this feature.
shared_arith_in
Chapter 2: Logic Array Blocks and Adaptive Logic Modules in Stratix IV Devices
carry_out
carry_in
labclk
D
D
reg0
reg1
Q
Q
To general or
To general or
To general or
To general or
local routing
local routing
local routing
local routing
February 2011 Altera Corporation
Adaptive Logic Modules