Stratix IV FPGA Core Fabric Architecture
The core fabric of Stratix® IV FPGAs is built from innovative logic units known as adaptive logic modules (ALMs). The ALMs are routed with the MultiTrack interconnect architecture, enabling Stratix IV FPGAs to implement high-speed logic, arithmetic, and register functions.
Stratix IV FPGAs carry forward the validated advantages of the innovative ALM logic structure as demonstrated by Stratix III FPGAs on OpenCore designs. The ALMs are fully integrated in Quartus® II software to easily deliver the highest performance, highest logic utilization, and lowest compile times.
Adaptive Logic Module
The key to high-performance Stratix IV FPGAs is the area-efficient ALM. It has 8 inputs with a fracturable look-up table (LUT) that can be divided into two adaptive LUTs (ALUTs) using Altera's patented LUT technology. Each ALM is capable of:
- A full 6-input LUT or select 7-input LUT
- Two independent outputs of multiple combinations of smaller LUT sizes for efficient logic packing
- Implementing complex logic-arithmetic functions without additional resources
See Figure 1 for the ALM structure, and Table 1 for more detailed information on the features available.
Figure 1. Stratix IV FPGA ALM
| Table 1. Stratix IV FPGA ALM Features and Advantages |
| Available Resources per ALM |
Advantages |
| 8-Input Fracturable LUT |
- Can implement any 6-input logic function and certain 7-input functions and be fractured into independent smaller LUTs, such as two independent 4-input LUTs
- Quartus II software design suite integrates this fracturability and optimizes it for performance, efficiency, power, and area (more logic capacity and less wasted logic)
|
| Two Embedded Adders |
- Allows for two two-bit additions or two three-bit additions without any additional resources
- Operands can be generated from the same ALM and do not require any additional logic
|
| Two Registers |
- Optimal register-to-logic ratio to ensure device is not register-limited
- Abundance in registers for register-rich applications or pipeline designs for performance
|
| Two Outputs |
- Inputs of a single ALM can be divided between the two output functions, allowing wide input functions to run fast and narrow input functions to efficiently use remaining resources
|
| MLAB |
- Stratix IV FPGA core is a second variation of the logic array block (LAB), known as the MLAB, that can be used as a regular ALM or configured as simple dual-port SRAM blocks
- Part of the TriMatrix memory technology, MLABs can be configured as 64 x 10 or 32 x 20 simple dual-port SRAM blocks. The MLABs are optimized to implement filter delay lines, small FIFO buffers, and shift registers with maximum performance of 600-MHz clock speeds
|
For more information, refer to the Logic Array Blocks & Adaptive Logic Modules (PDF) chapter of the Stratix IV Device Handbook.
The MultiTrack Interconnect
Stratix IV FPGAs leverage the MultiTrack interconnect technology. This technology consists of continuous, performance-optimized routing lines of different lengths used for communication within and between distinct design blocks.
The MultiTrack interconnect technology, shown in Figure 2, is used in Altera's Stratix FPGA series to:
- Provide the industry's best connectivity with up to five times the logic in a single hop (compared to the competition)
- Provide more accessibility to any surrounding LAB with much fewer connections, thus improving performance and reducing power
- Avoid area congestion to provide better logic packing
Figure 2. Stratix FPGA Series MultiTrack Interconnect Connectivity
Advantages of Stratix IV FPGA Architecture
The fracturable LUT, two full adders, two registers, and additional logic enhancements that enable the ALM to be partitioned into two independent LUTs for maximizing efficiency make Stratix IV FPGAs the fastest and biggest 40-nm FPGAs—with no wasted logic. Stratix IV devices are:
- 35 percent faster and can effectively pack 80 percent more logic compared to the nearest competing logic cell, thereby cutting costs by packing more logic in a smaller, less expensive device
- Fully integrated in Quartus II software to optimally utilize the 8-input fracturable LUT in the ALM and the MultiTrack routing interconnect architecture, and improve productivity by easily and reliably meeting timing closure
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