Simulation, FPGA, Emulation - How Do You Test a Chip Before Manufacturing?

In previous posts, we learned about:

• Verification
• Synthesis
• Place & Route
• STA

But there’s still a big question:

How do you really know the chip will work before manufacturing it?

Because after the chip is manufactured:

• It can’t be changed
• Fixing costs a fortune
• If there’s a major bug - the entire project might fail

Therefore, before manufacturing, you need to test the chip in every possible way.

And there are three main tools for this:

1. Simulation
2. FPGA - Testing on programmable hardware
3. Emulation - Full emulation

1. Simulation

This is the most basic tool.

What Is Simulation?

Simulation is a process where:

• You take the RTL
• You take the Testbench
• You run a “simulator”
• You see how signals change over time

It’s a virtual execution of the chip.

What Do You See in Simulation?

• How signals pass between modules
• What the values are at any given moment
• Where bugs get stuck
• How the system responds to different inputs

Why Is Simulation Important?

Because it’s:

• Cheap
• Relatively fast
• Allows testing countless scenarios
• Helps identify bugs early

But it has one big problem:

It’s very slow compared to actual hardware.

Simulating one second of chip operation can take hours (and sometimes days) on a computer.

So when you want to test more complex things - you move to more advanced tools.

2. FPGA - Field Programmable Gate Array

FPGA is a special chip that can be reprogrammed.

What Is an FPGA?

FPGA is physical hardware that contains:

• Millions of logic gates
• Programmable blocks
• Flexible connections

You can “load” your design into it - and it will behave like your chip.

Why FPGA?

Because:

• It’s a million times faster than simulation
• Works in real-time
• Allows testing the chip on an actual system
• Allows running actual software on it

FPGA is a “beta version” of the chip.

How Does It Work?

1. Take the RTL or Netlist
2. “Burn” it to the FPGA
3. Connect the FPGA to a system
4. Run actual code on it
5. Test system behavior

FPGA gives enormous confidence before moving to manufacturing.

What Are the Drawbacks of FPGA?

• It’s not identical to the final chip
• It’s slower than the actual chip
• It doesn’t support all features
• Sometimes it’s large and expensive

But despite everything - it’s a critical tool in the development process.

3. Emulation

Emulation is an intermediate stage between Simulation and FPGA.

What Is Emulation?

Emulation is a large hardware system that simulates the chip:

• Using arrays of FPGAs
• Or special hardware
• That allows running the entire chip in real-time

It’s like a “testing lab” that simulates the chip at high speed.

Why Emulation?

Because:

• Faster than simulation (thousands of times and more)
• Allows testing complex scenarios
• Allows running a complete operating system on the chip
• Allows testing integration with other components

Emulation is suitable for large and complex chips.

How Does It Work?

1. Upload the design to the Emulation system
2. Connect it to a complete system
3. Run actual software
4. Test interaction with other components
5. Verify everything works as expected

Emulation is the closest test to an actual chip.

When Do You Use Each Tool?

Stage	Tool	Speed	Accuracy	Use
Early development	Simulation	Very slow	High	Logic testing
Integration testing	FPGA	Fast	Medium	System testing
Final testing	Emulation	Very fast	Very high	Complete testing
Manufacturing	Actual chip	Fastest	100%	Final product

An Analogy to Clear Things Up

Think about car development:

Simulation: Testing on computer - how the engine will behave, how the brakes will work.

FPGA: Building a simple prototype - a car you can drive, but not perfect.

Emulation: Building a complete prototype - a car almost identical to the final one.

Actual chip: The final car that goes to market.

Summary

Before manufacturing a chip, it’s tested in three ways:

1. Simulation - Virtual execution, slow but accurate
2. FPGA - Testing on actual hardware, fast and convenient
3. Emulation - Complete testing at high speed

Only after all these tests pass successfully - you proceed to Tapeout.

Each of these tools is important at a different stage, and together they ensure the chip will be correct.

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In the next post, we’ll learn about Tapeout - the exciting stage where the design is sent to manufacturing, and what happens afterward until you get an actual chip.