What is Renode?

Whole-system Emulator

• CPU cores
• Peripherals
• Interconnections

Target platforms

• Windows
• Mac
• Linux
• • CI

CPU Cores

• x86
• arm
• arm64
• ppc
• riscv
• spark
• xtensa

Peripherals

Peripherals Are Just Special Memory

• Writing to a memory address does a thing
• Reading from an address gets a result
• Interrupts are just GPIOs

10% of the Functionality Gets You 90% of the Way There

• E.g. in a serial device, baudrate, timers, and parity/stop can be ignored
• Just "Tx", "Rx", and interrupt setup
• Most software works just fine if you return zeroes for invalid addresses

SVD files are your friend

• Your chip probably comes with a SVD file
• This gives a map of RAM and peripherals
• Renode can parse this and use it for logging / defaults

Existing Peripherals in Renode

• Built-in peripherals for a number of devices
• STM32
• NRF52
• IMXRT
• LiteX
• See https://github.com/renode/renode-infrastructure/tree/master/src/Emulator/Peripherals/Peripherals for more

Creating Peripherals

• Renode is written in C#
• Like Java, C# has an `eval()` function
• Peripherals can be written and loaded at runtime

Networks in Renode

• Built-in support for CAN, Ethernet, and Wireless
• Also possible to add networks at runtime
• No latency, just packets of data
• Different devices run at different speeds

Other Goodies

• LCD monitor with touchscreen support
• Python interpreter for quick hacks
• Attach GDB to any CPU core
• Attach a serial port to a network connection
• Scriptable with Robot framework
• Log function calls

Shortcomings

• Unable to unload modules
• Need to restart Renode when you change a file
• No real audio support
• Support for verifying I2S, but can't play it
• Only x64 hosts
• Runs under Rosetta on Mac
• Documentation needs work
• Use the source!

Extending Renode

First, Betrusted

• FPGA with VexRiscv
• 2nd FPGA with smaller VexRiscv
• 16-bit COM bus between them
• AES extensions
• x25519 "ENGINE" accelerator
• SHA accelerator
• Battery charger and manager
• Custom lcd, timers, and USB

Emulating it under Renode

• Good enough to develop the OS!
• Good enough to catch bugs

ENGINE bug

1. Added test vectors to the OS
2. Ran test vectors on physical device
3. Got test vectors passing in Renode
4. • Yay!
5. Someone (without a device!) decided to add more vectors
6. Tested in Renode
7. Passed
8. Failed on hardware
9. Bug in detecting overflow condition for normalization in hardware
10. https://github.com/betrusted-io/gateware/commit/817e284a3d92037b8cb0686735578d2bb60853e9

Getting Started with Renode

1. Renode Platform Definition (.repl)
2. Renode Script (.resc)

Example project repl

Example project resc

Running it

How to Extend Renode

1. Find a peripheral that does what you want
2. • You might even find a compatible peripheral!
3. Copy it to your project
4. Change the constructor
5. Change the register set
6. Import the `.cs` file into Renode
7. Add it to your platform file

Demonstration!

Running Badge Software in Renode

It Doesn't

Xtensa is a New Architecture

• Added support for ESP32 family
• Merged quickly
• Few others use Xtensa

Extensive use of Boot ROM

• Pulled ROM off device with esptool
• Load into RAM
• Set entrypoint

Add a serial port

• Immediately get output
• Breaks immediately

Load SVD file

Add Peripherals

Slowly Advance

What's Left

• SPI Controller
• Interrupt Controller