Variable Precision DSP Blocks User Guide: Agilex™ 3 FPGAs and SoCs

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ID 849313
Date 8/06/2025
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Document Table of Contents
Document Table of Contents x
1. Agilex™ 3 Variable Precision DSP Blocks Overview 2. Agilex™ 3 Variable Precision DSP Blocks Architecture 3. Agilex™ 3 Variable Precision DSP Blocks Operational Modes 4. Agilex™ 3 Variable Precision DSP Blocks Design Considerations 5. Native Fixed Point DSP Agilex FPGA IP References 6. Native Floating Point DSP Agilex FPGA IP References 7. Native AI Optimized DSP Agilex™ FPGA IP References 8. Multiply Adder FPGA IP References 9. ALTMULT_COMPLEX FPGA IP References 10. LPM_MULT FPGA IP References 11. LPM_DIVIDE (Divider) FPGA IP References 12. Document Revision History for the Variable Precision DSP Blocks User Guide: Agilex™ 3 FPGAs and SoCs
1. Agilex™ 3 Variable Precision DSP Blocks Overview x
1.1. Features 1.2. Supported Operational Modes in Agilex™ 3 Devices
1.2. Supported Operational Modes in Agilex™ 3 Devices x
1.2.1. Fixed-point Arithmetic 1.2.2. Floating-point Arithmetic
2. Agilex™ 3 Variable Precision DSP Blocks Architecture x
2.1. Fixed-point Arithmetic 2.2. Floating-point Arithmetic 2.3. Tensor Mode
2.1. Fixed-point Arithmetic x
2.1.1. Input Register Bank for Fixed-point Arithmetic 2.1.2. Pipeline Registers for Fixed-point Arithmetic 2.1.3. Pre-adder for Fixed-point Arithmetic 2.1.4. Internal Coefficient for Fixed-point Arithmetic 2.1.5. Multipliers for Fixed-point Arithmetic 2.1.6. Adder or Subtractor for Fixed-point Arithmetic 2.1.7. Accumulator, Chainout Adder, and Preload Constant for Fixed-point Arithmetic 2.1.8. Systolic Register for Fixed-point Arithmetic 2.1.9. Double Accumulation Register for Fixed-point Arithmetic 2.1.10. Output Register Bank for Fixed-point Arithmetic
2.2. Floating-point Arithmetic x
2.2.1. Input Register Bank for Floating-point Arithmetic 2.2.2. Pipeline Registers for Floating-point Arithmetic 2.2.3. Multipliers for Floating-point Arithmetic 2.2.4. Adder or Subtractor for Floating-point Arithmetic 2.2.5. Output Register Bank for Floating-point Arithmetic 2.2.6. Exception Handling for Floating-point Arithmetic
3. Agilex™ 3 Variable Precision DSP Blocks Operational Modes x
3.1. Operational Modes for Fixed-point Arithmetic 3.2. Operational Modes for Floating-point Arithmetic 3.3. Operational Modes for Tensor Mode
3.1. Operational Modes for Fixed-point Arithmetic x
3.1.1. Independent Multiplier Mode 3.1.2. Multiplier Adder Sum Mode 3.1.3. Independent Complex Multiplier 3.1.4. Systolic FIR Mode
3.1.1. Independent Multiplier Mode x
3.1.1.1. 18 × 18 or 18 × 19 Independent Multiplier 3.1.1.2. 27 × 27 Independent Multiplier
3.1.2. Multiplier Adder Sum Mode x
3.1.2.1. 8 x 8 (Unsigned) or 9 x 9 (Signed) Sum of 6 Mode
3.1.2.1. 8 x 8 (Unsigned) or 9 x 9 (Signed) Sum of 6 Mode x
3.1.2.1.1. 18 × 19 Multiplication Summed with 36-Bit Input Mode
3.1.4. Systolic FIR Mode x
3.1.4.1. Mapping Systolic Mode User View to Variable Precision Block Architecture View 3.1.4.2. 18-bit Systolic FIR Mode 3.1.4.3. 27-Bit Systolic FIR Mode
3.2. Operational Modes for Floating-point Arithmetic x
3.2.1. FP32 Single-precision Floating-point Arithmetic Functions 3.2.2. FP16 Half-precision Floating-point Arithmetic Functions 3.2.3. Multiple Floating-point Variable DSP Blocks Functions
3.2.1. FP32 Single-precision Floating-point Arithmetic Functions x
3.2.1.1. FP32 Multiplication Mode 3.2.1.2. Adder or Subtract Mode 3.2.1.3. Multiply Accumulate Mode 3.2.1.4. FP32 Vector One Mode 3.2.1.5. FP32 Vector Two Mode
3.2.2. FP16 Half-precision Floating-point Arithmetic Functions x
3.2.2.1. FP16 Supported Precision Formats 3.2.2.2. Sum of Two FP16 Multiplication Mode 3.2.2.3. Sum of Two FP16 Multiplication with FP32 Addition Mode 3.2.2.4. Sum of Two FP16 Multiplication with Accumulation Mode 3.2.2.5. FP16 Vector One Mode 3.2.2.6. FP16 Vector Two Mode 3.2.2.7. FP16 Vector Three Mode
3.2.3. Multiple Floating-point Variable DSP Blocks Functions x
3.2.3.1. Multiply-Add or Multiply-Subtract Mode 3.2.3.2. Direct Vector Dot Product 3.2.3.3. Complex Multiplication
3.3. Operational Modes for Tensor Mode x
3.3.1. Data Input Feed Preloading Method 3.3.2. Side Input Feed Preloading Method 3.3.3. Tensor Floating-point Mode 3.3.4. Tensor Fixed-point Mode 3.3.5. Tensor Accumulation Mode
3.3.3. Tensor Floating-point Mode x
3.3.3.1. Input Register Bank for Tensor Floating-point Mode 3.3.3.2. Pipeline Registers for Tensor Floating-point Mode 3.3.3.3. Cascade Signals for Tensor Floating-point Mode 3.3.3.4. Output Registers for Tensor Floating-point Mode
3.3.4. Tensor Fixed-point Mode x
3.3.4.1. Input Register Bank for Tensor Fixed-point Mode 3.3.4.2. Pipeline Registers for Tensor Fixed-point Mode 3.3.4.3. Cascade Signals for Tensor Fixed-point Mode 3.3.4.4. Output Registers for Tensor Fixed-point Mode
3.3.5. Tensor Accumulation Mode x
3.3.5.1. Input Register Bank for Tensor Accumulation Mode 3.3.5.2. Pipeline Registers for Tensor Accumulation Mode 3.3.5.3. Cascade Signals for Tensor Accumulation Mode 3.3.5.4. Output Registers for Tensor Accumulation Mode
4. Agilex™ 3 Variable Precision DSP Blocks Design Considerations x
4.1. Fixed-point Arithmetic 4.2. Floating-point Arithmetic 4.3. DSP Block Cascade Limit in Agilex™ 3 Devices
4.1. Fixed-point Arithmetic x
4.1.1. Configurations for Input, Pipeline, and Output Registers 4.1.2. Internal Coefficient and Pre-Adder for Fixed-point Arithmetic 4.1.3. Accumulator for Fixed-point Arithmetic 4.1.4. Input Cascade for Fixed-point Arithmetic 4.1.5. Chainout Adder/Accumulator Feature
4.1.1. Configurations for Input, Pipeline, and Output Registers x
4.1.1.1. Restrictions for Input Registers 4.1.1.2. Restrictions for Pipeline Registers 4.1.1.3. Supported Register Configurations per Operation Modes
4.1.4. Input Cascade for Fixed-point Arithmetic x
4.1.4.1. Dynamic Scanin
4.2. Floating-point Arithmetic x
4.2.1. Configurations for Input, Pipeline, and Output Registers 4.2.2. Chainout Adder
4.2.1. Configurations for Input, Pipeline, and Output Registers x
4.2.1.1. FP32 Operation Modes Supported Register Configurations 4.2.1.2. FP16 Operation Mode Supported Register Configurations
5. Native Fixed Point DSP Agilex FPGA IP References x
5.1. Native Fixed Point DSP Agilex™ FPGA IP Release Information 5.2. Supported Operational Modes 5.3. Maximum Input Data Width for Fixed-point Arithmetic 5.4. Maximum Output Data Width for Fixed-point Arithmetic 5.5. Parameterizing Native Fixed Point DSP IP 5.6. Native Fixed Point DSP Agilex™ FPGA IP Signals 5.7. IP Migration
5.3. Maximum Input Data Width for Fixed-point Arithmetic x
5.3.1. Using Less Than 36-Bit Operand In 18 x 18 Plus 36 Mode Example
5.5. Parameterizing Native Fixed Point DSP IP x
5.5.1. Operation Mode Tab 5.5.2. Input Cascade Tab 5.5.3. Pre-adder Tab 5.5.4. Internal Coefficient Tab 5.5.5. Accumulator/Output Chaining 5.5.6. Pipelining 5.5.7. Clear Signal
5.6. Native Fixed Point DSP Agilex™ FPGA IP Signals x
5.6.1. 9 × 9 Sum of 6 Mode Signals 5.6.2. 16 × 16 Complex Multiplier Mode Signals 5.6.3. 18 × 18 Full Mode Signals 5.6.4. 18 × 18 Sum of Two Mode Signals 5.6.5. 18 × 18 Plus 36 Mode Signals 5.6.6. 18 × 18 Systolic Mode Signals 5.6.7. 27 × 27 Mode Signals
6. Native Floating Point DSP Agilex FPGA IP References x
6.1. Native Floating Point DSP Agilex™ FPGA IP Release Information 6.2. Native Floating Point DSP Agilex™ FPGA IP Supported Operational Modes 6.3. Parameterizing the Native Floating Point DSP Agilex™ FPGA IP 6.4. Native Floating Point DSP Agilex™ FPGA IP Core Signals 6.5. IP Migration
6.3. Parameterizing the Native Floating Point DSP Agilex™ FPGA IP x
6.3.1. General Tab 6.3.2. Registers Tab
6.4. Native Floating Point DSP Agilex™ FPGA IP Core Signals x
6.4.1. FP32 Multiplication Mode Signals 6.4.2. FP32 Addition or Subtraction Mode Signals 6.4.3. FP32 Multiplication with Addition or Subtraction Mode Signals 6.4.4. FP32 Multiplication with Accumulation Mode Signals 6.4.5. FP32 Vector One and Vector Two Modes Signals 6.4.6. Sum of Two FP16 Multiplication Mode Signals 6.4.7. Sum of Two FP16 Multiplication with FP32 Addition Mode Signals 6.4.8. Sum of Two FP16 Multiplication with Accumulation Mode Signals 6.4.9. FP16 Vector One and Vector Two Modes Signals 6.4.10. FP16 Vector Three Mode Signals
7. Native AI Optimized DSP Agilex™ FPGA IP References x
7.1. Native AI Optimized DSP Agilex™ FPGA IP Release Information 7.2. Native AI Optimized DSP Agilex™ FPGA IP Supported Operational Modes 7.3. Parameterizing the Native AI Optimized DSP Agilex™ FPGA IP 7.4. Native AI Optimized DSP Agilex™ FPGA IP Signals 7.5. IP Migration
7.3. Parameterizing the Native AI Optimized DSP Agilex™ FPGA IP x
7.3.1. Operation Mode Tab 7.3.2. Clock Source Enable/Clear Tab
7.4. Native AI Optimized DSP Agilex™ FPGA IP Signals x
7.4.1. Tensor Floating-point Mode Signals 7.4.2. Tensor Fixed-point Mode Signals 7.4.3. Tensor Accumulation Mode Signals
8. Multiply Adder FPGA IP References x
8.1. Multiply Adder FPGA IP Release Information 8.2. Features 8.3. Parameters 8.4. Signals
8.2. Features x
8.2.1. Pre-adder 8.2.2. Systolic Delay Register 8.2.3. Pre-load Constant 8.2.4. Double Accumulator
8.2.1. Pre-adder x
8.2.1.1. Pre-adder Simple Mode 8.2.1.2. Pre-adder Coefficient Mode 8.2.1.3. Pre-adder Input Mode 8.2.1.4. Pre-adder Square Mode 8.2.1.5. Pre-adder Constant Mode
8.3. Parameters x
8.3.1. General Tab 8.3.2. Extra Modes 8.3.3. Multipliers Tab 8.3.4. Preadder Tab 8.3.5. Accumulator Tab 8.3.6. Systolic/Chainout Tab 8.3.7. Pipelining Tab
9. ALTMULT_COMPLEX FPGA IP References x
9.1. ALTMULT_COMPLEX FPGA IP Release Information 9.2. Features 9.3. Parameters 9.4. Signals
10. LPM_MULT FPGA IP References x
10.1. LPM_MULT FPGA IP Release Information 10.2. Features 10.3. Parameters 10.4. Signals
10.3. Parameters x
10.3.1. General Tab 10.3.2. General 2 Tab 10.3.3. Pipelining Tab
11. LPM_DIVIDE (Divider) FPGA IP References x
11.1. LPM_DIVIDE FPGA IP Release Information 11.2. Features 11.3. Verilog HDL Prototype 11.4. VHDL Component Declaration 11.5. VHDL LIBRARY_USE Declaration 11.6. Ports 11.7. Parameters
11.7. Parameters x
11.7.1. General Tab 11.7.2. General1 Tab
1. Agilex™ 3 Variable Precision DSP Blocks Overview
2. Agilex™ 3 Variable Precision DSP Blocks Architecture
3. Agilex™ 3 Variable Precision DSP Blocks Operational Modes
4. Agilex™ 3 Variable Precision DSP Blocks Design Considerations
5. Native Fixed Point DSP Agilex FPGA IP References
6. Native Floating Point DSP Agilex FPGA IP References
7. Native AI Optimized DSP Agilex™ FPGA IP References
8. Multiply Adder FPGA IP References
9. ALTMULT_COMPLEX FPGA IP References
10. LPM_MULT FPGA IP References
11. LPM_DIVIDE (Divider) FPGA IP References
12. Document Revision History for the Variable Precision DSP Blocks User Guide: Agilex™ 3 FPGAs and SoCs

2.3. Tensor Mode

In Tensor mode, there are two DOT engines and ALUs arranged as two columns as shown in the following figure.

Figure 17. Tensor Mode High-Level Block Diagram

The DOT engine computes the fixed-point product of 10 individual 8-bit data inputs and 10 pre-loaded 8-bit buffers, and sums all of the results together. The data inputs are common between the two columns and there are two separate sets of buffers per column intended for storing weights.

A load_buf_sel signal controls which set of weight is active. This allows one set to be updated while the other set is being used for computations. The DOT product outputs from each column are fed into independent ALUs.

Figure 18. DOT Engine for a Single Column
There are three operational modes:
  • Tensor Floating-point Mode
    • The DOT engine feeds the ALU which operates in floating-point mode. A shared exponent is supplied with the input data and separate shared exponents are loaded into the two sets of ping pong buffers. These shared exponents are used in the ALU to perform a fixed-point to floating-point conversion. It represents and manipulates rational numbers and operates in the floating-point format (IEEE-754 standard).
  • Tensor Fixed-point Mode
    • The DOT engine feeds the ALU which operates in fixed-point mode. It represents and manipulates integers and fixed-point numbers.
  • Tensor Accumulation Mode
    • The DOT engine is bypassed and ALU operates in floating-point mode. A 32-bit floating-point input is supplied directly to the ALU for each column. It represents and manipulates rational numbers and operates in the floating-point format (IEEE-754 standard).

In all three operational modes, the ALU features an accumulator and cascade signals between DSP blocks.

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