Introduction
ARM and FPGA are two very different types of processors used for a wide range of applications. Understanding the key differences between these architectures is important when selecting the right processor for a given application.
This article will provide an overview of ARM and FPGA processors, compare their architectures and performance attributes, analyze their programming approaches, and highlight suitable applications for each technology. Key differences will be summarized in tables throughout the article.
ARM Processors Overview
ARM processors are 32-bit and 64-bit RISC (Reduced Instruction Set Computer) CPUs that are designed for low cost and power efficiency. ARM cores are extremely popular in mobile and embedded devices due to their minimalist, power-optimized architecture.
Some key attributes of ARM processors:
- RISC architecture with simpler instructions that execute in single clock cycles
- Fixed hardware logic and execution pipelines
- Excellent energy efficiency and low heat dissipation
- Scalable performance from microcontrollers to application processors
- Available as standardized cores licensed to many vendors
- Requires software development in C/C++ or Assembly
ARM cores are used in billions of devices including smartphones, tablets, microcontrollers, and other embedded systems. Leading vendors like Qualcomm, Samsung, Nvidia, AMD, and Apple design their own ARM-based chips.
FPGA Processors Overview
FPGAs (Field Programmable Gate Arrays) are integrated circuits that can be programmed and reconfigured after manufacturing. This enables an FPGA to effectively morph into a custom computing device tailored for each application.
Key attributes of FPGAs:
- Flexible fabric of logic blocks and routing that can be reconfigured
- Parallel processing architecture optimized for data flow applications
- Hardware level programmability using HDLs like Verilog or VHDL
- High performance potential for parallel workloads
- Well suited for DSP, ML, image processing, etc
- Widely used for hardware acceleration and prototyping
While not as ubiquitous as ARM chips, FPGAs are popular for niche applications requiring custom hardware-level optimization and processing.
Architecture Comparison
ARM and FPGA processors have fundamental differences in their architecture and implementation:
| Parameter | ARM Processor | FPGA |
|---|---|---|
| Design Philosophy | RISC fixed architecture | Reconfigurable fabric |
| Processing Approach | Sequential von Neumann | Parallel dataflow |
| Execution Logic | Fixed pipelines and data paths | Reprogrammable logic blocks + routing |
| Hardware Flexibility | None, fixed function | Highly flexible, customizable logic |
| Software Flexibility | High, can run different OS & apps | Limited without HW changes |
| Performance Attributes | Predictable | Application dependent |
| Programming | C/C++, Assembly | HDL (Verilog/VHDL) |
| Development Approach | Software algorithms | Hardware logic synthesis |
This table summarizes the key architectural differences between the two technologies:
RISC vs Reconfigurable Logic Architecture
The core design philosophy behind ARM and FPGA processors are completely different. The RISC architecture used in ARM chips has fixed hardware logic blocks tuned for efficiency in executing software instructions. In contrast, FPGAs contain a flexible fabric of logic blocks with programmable interconnects that can be rewired as needed.
Sequential vs Parallel Processing
ARM uses a classic sequential von Neumann architecture where instructions are executed one after another. FPGAs employ a dataflow architecture that processes data in parallel through customized pipelines. Multiple operations can occur simultaneously.
Fixed Pipelines vs Reconfigurable Logic
ARM processors rely on hardwired logic blocks and execution pipelines tailored for RISC instructions. With FPGAs, any hardware function can be synthesized using the basic logic elements, letting you customize data paths and control logic.
Software vs Hardware Flexibility
ARM processors are software-flexible – different operating systems and applications can run on the same ARM core. FPGAs are the opposite – they are hardware-flexible and must be physically reprogrammed for new functions, but software is largely fixed.
This contrast in fundamental architecture leads to major differences in performance, programming, and use cases.
Performance Comparison
Both ARM and FPGA offer excellent performance, but in very different ways:
| Performance Attribute | ARM Processor | FPGA |
|---|---|---|
| Processing Style | Sequential | Parallel |
| Clock Speeds | Up to ~3 GHz | Typically 100-400 MHz |
| Latency | 10s – 100s of cycles | Single cycle throughput |
| Throughput | Gigabytes/sec | Terabytes/sec potential |
| Performance Scale | Up to multicore CPUs | 10X-100X speedups possible |
| Power Efficiency | Excellent | Configurable for efficiency |
| Cost Efficiency | Low cost per unit | High development costs |
Let’s analyze the key performance differences:
Sequential vs Parallel Execution
The von Neumann nature of ARM processors means they execute operations sequentially, albeit with some instruction parallelism via pipelines. FPGAs process data simultaneously in customized parallel pipelines, enabling much higher throughput. However, latency is lower on ARM cores.
Clock Speed Differences
ARM cores reach clock speeds up to around 3 GHz today by optimizing critical paths for fast sequential execution. FPGAs typically run at 100-400 MHz but make up for lower clocks through massive parallelism.
Throughput and Latency
ARM processors can complete single operations faster due to higher clocks (latency in 10s-100s of cycles). However, FPGA throughput for highly parallel tasks like encryption or image processing can be orders of magnitude higher (terabytes/sec).
Performance Scalability
ARM scales well to multicore CPUs with shared memory access. FPGAs can provide 10X-100X speedups for parallel workloads by customizing logic, but single thread performance lags.
Power and Cost Efficiency
ARM excels at power efficiency for mobile devices with clock gating and power management features. FPGAs can also be tuned for power efficiency but higher performance comes at a cost premium, while ARM chips leverage economies of scale.
For the right applications, FPGAs can significantly outperform ARM processors. But ARM remains superior for general purpose computing and single-threaded tasks.
Programming Model Comparison
ARM and FPGAs have completely different programming methodologies:
| Programming Attribute | ARM | FPGA |
|---|---|---|
| Primary Languages | C/C++, Assembly | Verilog, VHDL (HDLs) |
| Abstraction Level | Software algorithms | Hardware logic |
| Device Learning | Not required | Must learn FPGA fabric |
| Programming Approach | Procedural, sequential | Concurrent, parallel |
| Debugging | Software debugging | Hardware verification |
| Optimization | Compiler optimizations | Logic synthesis optimization |
Some key aspects:
Software vs Hardware Languages
ARM processors are programmed using software languages like C/C++ and Assembly to implement algorithms. FPGAs require hardware description languages (HDLs) like Verilog and VHDL that describe digital logic gates and connections.
Abstraction from Hardware
Software programmers can develop code without knowledge of the underlying processor. With FPGAs, you must understand the low-level fabric in order to synthesize logic that maps efficiently.
Programming Paradigm
ARM code is written procedurally with sequential instructions. FPGA logic must be designed concurrently with parallel data flows in mind. Different mental models are required.
Debugging and Optimization
Software debugging tools are more mature. FPGA optimization relies heavily on the synthesis tool mapping designs to the underlying hardware as efficiently as possible.
FPGA programming has a much steeper learning curve but enables hardware-level customization. ARM programming is more accessible thanks to abundant software resources.
Use Case Comparison
Given their differing attributes, ARM and FPGAs are suited for very different applications:
| Use Cases | ARM Processors | FPGAs |
|---|---|---|
| Mobile devices | Excellent fit | Not suitable |
| Embedded systems | Widely used | Overkill for most |
| IoT endpoints | Well suited | Premium use cases |
| Cloud acceleration | Limited suitability | Excellent fit |
| DSP algorithms | Capable for many apps | Higher performance possible |
| Computer vision | Often sufficient | More demanding apps benefit |
| Autonomous vehicles | Generally not used | Critical for some subsystems |
Here are some typical use cases that favor ARM or FPGAs:
Mobile Devices
ARM processors are designed for mobile applications where low power draw is critical. FPGAs are overkill for smartphones and tablets due to cost and power constraints.
Embedded Systems
ARM MCUs and application processors power most embedded electronics like home appliances, sensors, industrial, etc. FPGAs are usually too expensive for mainstream embedded use.
IoT Endpoints
ARM Cortex M class MCUs feature in most IoT endpoint designs. Some higher performance IoT applications utilize FPGAs where ML acceleration is required locally.
Cloud Acceleration
FPGAs are widely used to accelerate computationally intensive tasks in data centers by customizing parallel pipelines. ARM servers have limited suitability currently.
Computer Vision
Lower resolution computer vision runs well on ARM chips. But FPGA acceleration becomes important for higher resolution or when deep learning algorithms are used.
Autonomous Vehicles
ARM processors typically do not have the performance for autonomous vehicle subsystems. FPGAs are critical for sensor fusion, perception, and decision making.
For any given application, the tradeoffs between these technologies must be carefully evaluated when selecting a processing platform.
Conclusion
ARM and FPGA processors have fundamental differences in architecture, programming, performance attributes, and typical applications.
Key Takeaways:
- ARM processors feature a RISC architecture optimized for low cost and power efficiency. FPGAs provide a flexible fabric of logic blocks that can be reconfigured.
- ARM uses a sequential von Neumann architecture while FPGAs leverage parallel dataflow processing.
- FPGAs can accelerate suitable parallel workloads by 10X-100X but have a steep development curve. ARM offers broadly accessible software-based programming.
- ARM excels in mobile and embedded devices. FPGAs are used where custom hardware acceleration is critical.
Understanding these complementary technologies is important when architecting systems. With their respective strengths, ARM and FPGAs will continue powering many of the world’s electronic devices into the foreseeable future.
Frequently Asked Questions
What are the key differences between ARM and FPGA architectures?
ARM uses fixed RISC processor cores while FPGAs provide reconfigurable logic fabrics. ARM has a sequential von Neumann architecture whereas FPGAs use a parallel dataflow architecture.
When is ARM processors the best choice over FPGA?
ARM processors are superior for mobile applications, embedded systems, and general purpose computing where low cost and power efficiency are critical. Their software programmability is also more accessible.
When is FPGA the right choice over ARM processors?
FPGAs are chosen for applications requiring custom hardware acceleration and parallel processing. They excel in cloud acceleration, high performance DSP and computer vision algorithms, and critical autonomy systems.
Can ARM processors be reconfigured like FPGAs?
No, ARM processors have fixed architecture and cannot be reconfigured at the hardware level. FPGAs can be reprogrammed even after manufacturing to morph into customized accelerators.
Do FPGAs completely replace ARM processors?
No, FPGAs complement rather than replace ARM processors in most systems. ARM CPUs are still used to execute control, I/O and application layer software alongside FPGA acceleration. The technologies have different strengths.