GRAU: A Generic Runtime-Reconfigurable Activation-Requantization Unit for Quantized Neural Network Accelerators

arXiv:2602.22352 · cs.AR, cs.AI · Submitted 2026-02-25 · Read on arXiv

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Introduction to the show: ident: AI Radio. Generated commentary on the latest Artificial Intelligence papers.

Tom: I'm Tom.

Jane: And I'm Jane, here with Lu, Meng and our in-house large language model, Lalam.

Tom: We're looking at the paper: "GRAU: A Generic Runtime-Reconfigurable Activation-Requantization Unit for Quantized Neural Network Accelerators".

Jane: The gist The proposed Generic Reconfigurable Activation Unit (GRAU) is a novel hardware design that uses piecewise linear fitting with power-of-two approximations to achieve high hardware efficiency and flexibility for…

Tom: First, who's behind it and why it matters.

Title and authors: Jane: So let’s talk about what the title GRAU: A Generic Runtime-Reconfigurable Activation-Requantization Unit for Quantized Neural Network Accelerators tells us about this paper. It basically says they built a hardware unit that can be generic, reconfigurable, and handle requantization all at once for neural networks.

Tom: What I find interesting is the focus on runtime reconfiguration. It means the hardware isn't locked into one thing; it’s meant to adapt while you are running your model. That flexibility is what makes this different from older fixed designs where you had to bake in all your possibilities at the start.

Lu: And when you look at the authors, Yuhao Liu, Salim Ullah, and Akash Kumar from Ruhr University Bochum and Dresden University of Technology; they have a strong background in hardware design and scalable data analytics which makes sense for this kind of work.

Meng: I’m thinking about the actual hardware implementation mentioned. They claim it only requires basic comparators and one-bit right shifters, which is pretty lean for deployment on resource constrained chips that we deal with constantly at scale <ref:2602.22352#pg1,basic comparators and 1-bit right shifters>.

Jane: That's a huge point because it lowers the barrier for using this in production environments where power and area are critical constraints. It moves the discussion from just "can we run this?" to "how much power does it use when I run this specific model?".

Tom: And they’re tackling mixed-precision quantization right there, supporting things like two/four/eight-bit settings simultaneously, which is a major win for flexibility across different deployment scenarios <ref:2602.22352#pg2>.

Lu: It sets up the whole framework by folding Batch Normalization and output requantization into this unified activation processing unit, which simplifies the overall system design significantly.

Meng: So this isn't just about one part; it’s about simplifying the entire activation pipeline, which means less complex control logic to manage when you deploy it in a real traffic scenario.

Jane: It seems like they are aiming for a unified design that handles all these complexities without adding significant overhead to the overall system architecture. That simplification is what I find most compelling right now.

Tom: So we’ve seen the title and authors, and it points toward a hardware solution that aims to solve the inflexibility problem inherent in traditional activation units.

The paper's summary: Jane: Now let’s look at the actual summary of GRAU: A Generic Runtime-Reconfigurable Activation-Requantization Unit for Quantized Neural Network Accelerators. It says they developed a fast greedy piecewise linear fitting algorithm to replace the nonlinear activation folded with batch normalization and output re-quantization in Quantized Neural Networks.

Tom: That greedy algorithm is the engine here, right? It iteratively refines the approximation by finding the point with the maximum vertical distance between where you want to be and what you have. It sounds like a smart way to get a good fit without doing all that complex math upfront.

Lu: They show that they develop representations called PWLF, PoT-PWLF, and APoT-PWLF, which are then approximated using power-of-two slopes to handle things like SiLU. It’s about getting a representation that can model non-monotonic functions instead of just sticking to simple monotonic ones.

Meng: So they are replacing the old method with these new representations, and the key is that this framework supports multiple nonlinear and non-monotonic activations like ReLU, Sigmoid, and SiLU under four/eight-bit unified precision and two/four/eight-bit mixed settings <ref:2602.22352#pg2>.

Tom: That means you can run models using those complex functions without needing to switch to a completely different hardware implementation just because the activation function is non-monotonic.

Jane: It’s about making the hardware more software friendly, so the hardware adapts to whatever activation function your software demands, which is exactly what we need for modern AI deployment.

Lu: They developed this fast greedy piecewise linear fitting algorithm to replace that nonlinear activation folded with batch normalization and output re-quantization in Quantized Neural Networks, which is a big step in unifying the processing unit.

Meng: I’m looking at the experiments on CIFAR-ten and ImageNet with VGG16 and ResNet18 under those mixed settings, which tells us how this actually performs when we put it under some real load <ref:2602.22352#pg1>.

Tom: The results suggest that their approach is feasible to use for QNNs, and they show the feasibility of using these PoT/APoT approximations on CIFAR-ten and ImageNet with VGG16 and ResNet18 models under four/eight-bit unified-precision and two/four/eight-bit mixed-precision settings with various activation functions like ReLU, Sigmoid, and SiLU <ref:2602.22352#pg2>.

Jane: So the implication is that this approach is feasible to use for QNNs with those mixed settings, which means it’s not just a theoretical idea anymore; it’s showing results on standard models.

Lu: They also developed this fast greedy piecewise linear fitting algorithm to replace the nonlinear activation folded with batch normalization and output re-quantization in Quantized Neural Networks, which is a big step in unifying the processing unit.

Meng: I want to see those exploration results when they show how this scales beyond the small models they tested; real traffic at scale is where you find out if this hardware actually holds up under load.

Tom: The point they make is that their approach is feasible to use for QNNs, and they show the feasibility of using these PoT/APoT approximations on CIFAR-ten and ImageNet with VGG16 and ResNet18 models under four/eight-bit unified-precision and two/four/eight-bit mixed-precision settings with various activation functions like ReLU, Sigmoid, and SiLU <ref:2602.22352#pg2>.

The paper's improvements: Tom: So let’s talk about the specific improvements they suggest in GRAU. The big one is that it cuts hardware footprint by over ninety percent compared to multi-threshold units. This reduction in LUT consumption means we can finally build smaller chips for edge devices.

Jane: It’s a design that supports mixed precision quantization and lets you reconfigure the activation unit at runtime just by updating a few registers for different functions or precisions, which is what makes it so flexible.

Lu: They also pointed out that scaling up the number of segments is often more efficient than trying to increase the exponent number in the slope approximation. That gives us a clear rule for how to optimize the hardware budget when we are designing these units from scratch.

Meng: For production, this means we can build much smaller, more power-efficient edge accelerators because the LUT consumption is so low and the ADP numbers are better than what we were using on those MT units.

Tom: The implication is that we can finally move beyond fixed hardware solutions and design something that adapts to the model itself while staying efficient.

Jane: It really sets a new baseline for generic activation hardware design in this space because it shows how much overhead you can actually reduce without losing accuracy on QNN models.

Lu: They plan to keep exploring the fine-grained approximation of these QNN models and do more design space exploration based on their PWLF algorithm for better results.

Meng: I’m still focused on what happens when we take this from simulation into real traffic, because that’s where you find out if it actually breaks at scale.

Tom: So, to wrap up, GRAU is this Generic Runtime-Reconfigurable Activation-Requantization Unit for Quantized Neural Network Accelerators which cuts hardware footprint by over ninety percent compared to multi-threshold units.

Jane: It’s a design that supports mixed precision quantization and lets you reconfigure the activation unit at runtime just by updating a few registers for different functions or precisions.

Lu: This work establishes a unified hardware design that enables runtime reconfiguration, multi-function support, and mixed-precision activation with significantly reduced overhead.

Conclusion: Tom: So we’re wrapping up on GRAU, which is this Generic Runtime-Reconfigurable Activation-Requantization Unit for Quantized Neural Network Accelerators which cuts hardware footprint by over ninety percent compared to multi-threshold units.

Lu: I think this is just the beginning; the real work now is in pushing that approximation accuracy when applied to more complex QNN structures.

Meng: Yeah, if they can push that refinement further, it could really make a difference in what we can actually ship to customers.

Tom: What’s next for this research is seeing how deep they can push that fine-grained approximation for the QNN models and do a proper design space exploration based on their PWLF algorithm.

Jane: And that exploration will tell us if this hardware is ready for the kind of real traffic we actually see in production environments.

Lu: Exactly, because the way you approximate those slopes determines how well it handles non-monotonic functions like SiLU or ReLU, which is a big part of what makes these activations useful.

Meng: If they can show that this hardware holds up under load with the accuracy they claim, then we’re looking at something that could actually be deployed widely on resource constrained chips.

Lalam: I'm just keeping my fingers crossed for those results; this paper sets a strong direction for building more flexible and efficient AI hardware.

Tom: That’s it for GRAU; it really shows how much efficiency we can gain when we move away from traditional fixed-threshold approaches in activation units.

Jane: We get to see a design that balances high efficiency with the need for flexibility across different models and precisions, which is really what we need in this field right now.

Ruhr University Bochum · Dresden University of Technology · Center for Scalable Data Analytics and Artificial Intelligence (ScaDS.AI Dresden/Leipzig)

cs.AR, cs.AI

Submitted: 2026-02-25

Updated: 2026-10-19

Comments: Accepted by FPT 2026 Special Session

Code: https://github.com/liuyh-Horizon/GRAU-Approx-Toolkit

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

Importance score: 78/100

The gist: The gist The proposed Generic Reconfigurable Activation Unit (GRAU) is a novel hardware design that uses piecewise linear fitting with power-of-two approximations to achieve high hardware efficiency

Key concepts

Piecewise Linear Fitting (PWLF): This is the core mathematical technique used to approximate complex nonlinear activation functions by breaking them into several straight line segments. The GRAU uses this method, approximating the slopes of these segments using powers of two, which makes the hardware implementation simpler and more efficient than standard methods.
Power-of-Two (PoT) and Additive Power-of-Two (APoT): These are specific approximations used to determine the steepness (slope) of the linear segments in the PWLF model. By approximating slopes with powers of two, the hardware implementation avoids complex calculations, allowing for efficient representation using simple logic gates and reducing hardware resource usage significantly.
Runtime Reconfigurability: The GRAU is designed to be flexible by allowing its internal structure to change while the chip is running. This reconfiguration is achieved by updating a small set of registers that control the segment breakpoints and shift encodings, enabling it to switch between different activation functions or quantization precisions on the fly.

Terminology

Quantization — 2× in this paper · explained in 14 episodes
Accuracy — 1× in this paper · explained in 1 episode

Summary

The gist The proposed Generic Reconfigurable Activation Unit (GRAU) is a novel hardware design that uses piecewise linear fitting with power-of-two approximations to achieve high hardware efficiency and flexibility for low-precision quantized neural network accelerators.

Motivation and Problem Statement

Classic multi-threshold activation hardware faces limitations such as exponential hardware scaling with precision, inefficiency in mixed-precision quantization, and an inability to represent non-monotonic activations like SiLU<ref:2602.22352#pg2> The Multi-Threshold (MT) activation unit requires a set of fixed thresholds for n-bit outputs, causing a rapid increase in hardware cost as precision increases However, the MT unit must implement the maximum number of thresholds required by the highest precision, which leads to exponential hardware resource consumption Furthermore, serial reuse of a comparator can reduce hardware costs but significantly increases latency at higher precisions

GRAU Design and Methodology

The GRAU design is based on piecewise linear fitting where the segment slopes are approximated by powers of two The core idea involves transforming the original nonlinear activation functions folded with Batch Normalization and output re-quantization into PWLF, PoT-PWLF, and APoT-PWLF representations compatible with the proposed GRAU architecture<ref:2602.22352#pg5> This transformation involves a three-step approximation process:

Adjusting the breakpoints of segments to their nearest integers
Approximating the slope of each segment in PWLF functions to the nearest PoT and APoT value
Choosing the left rounded breaking point of each segment to create a new linear function with approximated PoT and APoT slopes

The algorithm used for generating these approximations is a fast greedy piecewise linear fitting algorithm which employs a greedy integer-aware breakpoint selection strategy This algorithm starts from a single segment spanning the entire input range and iteratively refines the approximation by identifying the point with the maximum vertical distance between the target nonlinear function and the chord connecting the segment endpoints

Hardware Implementation and Efficiency

The GRAU hardware design requires only basic comparators and 1-bit right shifters, supporting mixed-precision quantization and nonlinear functions such as SiLU The implementation is realized in both pipelined and serialized variants to balance throughput and cost

**- Hardware Friendly and Runtime Reconfiguration: The design uses only comparators and a 1-bit shifter pipeline and can be reconfigured at runtime by updating a small set of breakpoint and shift-encoding registers It supports multiple nonlinear activations (e.g., ReLU, Sigmoid, SiLU) and easily adapts to different quantization precisions through lightweight reconfiguration of breakpoints and shifts The hardware resource consumption shows that both PoT-PWLF and APoT-PWLF activation units are much more LUT-efficient than the MT unit, reducing LUT usage by over 90% compared to Multi-Threshold (MT) units Furthermore, the lower ADP and PDP of the GRAU also show that our work has better power and design efficiency than the Multi-Threshold activation units The pipelined GRAU instances can support higher clock frequencies due to their low critical total path delay Moreover, within the proposed design, increasing the segment number is generally more LUT-efficient than increasing the exponent number Combined with the accuracy results, this suggests that allocating hardware budget to more segments is often more cost-effective than allocating it to more 2n candidates The implementation results show that our work can reduce more than 90% of the LUT consumption of Multi-Threshold-based generic activation functions, supporting higher clock frequencies with better power and hardware efficiency The total delay for the pipelined GRAU instances takes 24 cycles to complete one approximate nonlinear processing, which is slower than the 1/2/4-bit quantization of the Multi-Threshold activation unit However, considering that GRAU also has thresholds, it can support the 1/2-bit Multi-Threshold quantization with 1/3 thresholds The hardware results show that both PoT-PWLF and APoT-PWLF activation units are much more LUT-efficient than the MT unit, compared with the pipelined MT design requiring 10206 LUTs In contrast to the encoding setting in Figure 3, in the real hardware implementation, all shifting encodings are negative The final result will apply the sign bit and bias to complete the piecewise linear approximation for the activation unit The results suggest that allocating hardware budget to more segments is often more cost-effective than allocating it to more 2n candidates We will deeply explore the fine-grained approximation for the QNN models and the design space exploration of hardware based on our PWLF algorithm The paper concludes that we implemented the serialized and pipelined PoTPWLF and APoT-PWLF approximated Generic Reconfigurable Activation Unit (GRAU) in this work This implementation results show that our work can reduce more than 90% of the LUT consumption of Multi-Threshold-based generic activation functions, supporting higher clock frequencies with better power and hardware efficiency The paper aims to establish a unified activation hardware design that enables runtime reconfiguration, multi-function support, and mixed-precision activation with significantly reduced overhead The goal of this work is not to design a full accelerator architecture. Instead, we aim to establish a unified activation hardware design that enables runtime reconfiguration, multi-function support, and mixed-precision activation with significantly reduced overhead The paper concludes that the PoTPWLF and APoT-PWLF approximations result in a small accuracy loss compared to the original, accurate QNN models The implementation results show that our work can reduce more than 90% of the LUT consumption of Multi-Threshold-based generic activation functions, supporting higher clock frequencies with better power and hardware efficiency We will deeply explore the fine-grained approximation for the QNN models and the design space exploration of hardware based on our PWLF algorithm The paper concludes that we implemented the serialized and pipelined PoTPWLF and APoT-PWLF approximated Generic Reconfigurable Activation Unit (GRAU) in this work This implementation results show that our work can reduce more than 90% of the LUT consumption of Multi-Threshold-based generic activation functions, supporting higher clock frequencies with better power and hardware efficiency The paper aims to establish a unified activation hardware design that enables runtime reconfiguration, multi-function support, and mixed-precision activation with significantly reduced overhead The goal of this work is not to design a full accelerator architecture. Instead, we aim to establish a unified activation hardware design that enables runtime reconfiguration, multi-function support, and mixed-precision activation with significantly reduced overhead The paper concludes that the PoTPWLF and APoT-PWLF approximations result in a small accuracy loss compared to the original, accurate QNN models The implementation results show that our work can reduce more than 90% of the LUT consumption of Multi-Threshold-based generic activation functions, supporting higher clock frequencies with better power and hardware efficiency We will deeply explore the fine-grained approximation for the QNN models and the design space exploration of hardware based on our PWLF algorithm The paper concludes that we implemented the serialized and pipelined PoTPWLF and APoT-PWLF approximated Generic Reconfigurable Activation Unit (GRAU) in this work This implementation results show that our work can reduce more than 90% of the LUT consumption of Multi-Threshold-based generic activation functions, supporting higher clock frequencies with better power and hardware efficiency The paper aims to establish a unified activation hardware design that enables runtime reconfiguration, multi-function support, and mixed-precision activation with significantly reduced overhead The goal of this work is not to design a full accelerator architecture.

Improvements for AI systems

Bold hardware efficiency improvement through GRAU: The design reduces LUT consumption by over 90% compared with Multi-Threshold (MT) units, achieving higher frequency, lower Area-Delay-Product (ADP), and lower PowerDelay-Product (PDP). This allows for significantly smaller and more power-efficient edge accelerators for neural networks.
Flexibility in activation function support: GRAU supports multiple nonlinear and non-monotonic activations (e.g., ReLU, Sigmoid, SiLU) and easily adapts to different quantization precisions through lightweight reconfiguration of breakpoints and shifts. This enables the hardware to be repurposed for various network architectures without requiring a complete redesign.
Mixed-precision quantization capability: The unit supports mixed-precision quantization by using basic comparators and 1-bit right shifters, allowing for efficient implementation of models that utilize both 4/8-bit unified and various mixed precisions (2/4/8-bit).
Handling non-monotonic activations: Unlike Multi-Threshold units which are restricted, GRAU can handle functions like SiLU by using Piecewise Linearized Fitting (PWLF) with Power-of-Two (PoT) and Additive Powerof-Two (APoT) slope approximation, addressing the limitation where MT units inherently supports only monotonically increasing functions.
Runtime reconfigurability: The unit is designed for runtime reconfiguration by updating a small set of breakpoint and shift-encoding registers, which allows the hardware to be reconfigured at runtime for different activation functions or precision modes.