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ESP32 simulator, the classic one, on an Xtensa core

Mokxi models the thirty-pin DOIT ESP32 DevKit V1: an ESP32-WROOM-32 with its Xtensa LX6 at 240 MHz, the GPIO matrix, IO_MUX, UART0, timer group 0, ADC1 and the LEDC PWM controller, at the real addresses. One core, not two, and no radio (WiFi here is simulated, and says so), and the contract says exactly where every edge is.

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  • 9peripheral areas modeled
  • 5projects ready to run
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ESP32 DevKit V1: blinklive0.000 s 0.00x
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The board is running real firmware right now. Click it to open the circuit in the editor.
The model

What is modeled

Taken from the board's own contract document and put in plain words, with what is missing listed underneath.

Core
Xtensa LX6 in the windowed ABI, sixty-four address registers, the window overflow and underflow handlers, one instruction per cycle at 240 MHz
Memory
128 KB of instruction RAM at 0x4008_0000 and 192 KB of data RAM at 0x3FFB_0000, kept apart the way ESP-IDF keeps them
GPIO matrix and IO_MUX
Forty pins with the real two-register split, pulls and input enable per pad, and GPIO 34 to 39 refused as outputs, because the chip has no driver on them
UART0
Paced at the configured baud rate, wired to the serial monitor
Timer group 0
Timer 0 at a tick a microsecond behind millis() and micros(); delay() parks the core on CCOMPARE0 rather than spinning on it
ADC1
Twelve bits on the eight real channels (GPIO 36, 37, 38, 39, 32, 33, 34 and 35) with the four attenuations, 11 dB reaching 3.9 V
LEDC
The high-speed group: four timers and eight channels on any pin with an output driver, behind analogWrite, ledcAttach and ledcWrite
The interrupt matrix
Two sources routed the way the hardware routes them, so attachInterrupt is three writes rather than one
WiFi, simulated
WiFi.h, HTTPClient.h and WebServer.h over a network written in software: no radio, no 802.11, no real internet

Not in the model

  • A radio of any kind. There is no 802.11 and no Bluetooth in the model. WiFi is simulated instead (the Arduino API over a network of ours, with no real internet behind it), and every page that mentions it says so.
  • The second core. A real ESP32 has two LX6 cores; this model runs the PRO core, so anything that starts a task on core 1 will not run.
  • The FPU: every floating-point instruction faults rather than returning a wrong number, and the runtime is soft float.
  • The cache, flash and PSRAM, the RTC and ULP, deep sleep, ADC2, the touch and hall sensors, I2C, SPI, I2S and RMT.
  • Several addresses (the IO_MUX pad order, the timer group and LEDC layouts, the SENS offsets, the interrupt matrix numbers and the GPIO matrix signal indices LEDC uses) are this model’s belief rather than something it can stand behind. Section 6 of the contract names every one.
Start here

Open one and press Run

Each of these opens in the editor exactly as it is drawn here.

Projects

Every built-in project on the ESP32 DevKit V1

Each has its own page with the circuit running, the code and a parts list.

Learn

Tutorials that use this board

Each one ends in a running circuit, on this same board.

analogRead on an ESP32: 12 bits, attenuation and ADC2Uno vs ESP32 vs Pico: which to start with

Questions

Is it free?

Yes. Every board and every part is on the free plan, with no account needed.

Can I compile my own sketch for it?

Yes. Edit the sketch and press Run: it compiles in the tab with clang for Xtensa, and the build panel shows every step. Nothing is uploaded. Floating-point math is the one thing to avoid: this model has no FPU, so a float multiply faults rather than returning a wrong number.

Does it simulate WiFi or Bluetooth?

Bluetooth, no. WiFi, yes: simulated, and it says plainly that it is. Your sketch uses the real Arduino calls (WiFi.begin, WiFi.status, HTTPClient, WebServer), and the board joins a network, fetches a page and serves one. Underneath there is no radio, no 802.11 and no real internet: four made-up addresses under .mokxi exist and nothing a sketch does leaves this tab.

Why will pinMode(34, OUTPUT) not work?

Because it does not work on the chip either. GPIO 34 to 39 have an input buffer and no output driver at all. Mokxi refuses the write the way the silicon does, counts it, and puts a small amber mark on the board rather than letting you believe the pin is driving something.

Why does my potentiometer never reach 4095?

Because at the default 11 dB attenuation this converter’s full scale is about 3.9 V, and your rail is 3.3 V. About 3466 is the top of a 3.3 V sweep, and the knob example prints the raw number so it is not a mystery.

Is this the 30-pin or the 38-pin board?

The thirty-pin DOIT DevKit V1. The 38-pin Espressif DevKitC is a full inch between header rows and brings out six more pins: the GPIO numbers are the same chip’s, the positions are not.

Does it run both cores?

One. The PRO core runs; there is no APP CPU and no FreeRTOS to schedule across them, so a setup()/loop() sketch is fine and xTaskCreatePinnedToCore is not.

Also here

The other boards

Every one of these runs today, and every one is free.

Looking for the shorter introduction? See the ESP32 DevKit simulator page.

ESP32-C3-DevKitM-1
runs now
A RISC-V core at 160 MHz with GPIO, UART, the SYSTIMER, a twelve-bit ADC on GPIO 0 to 4 and LEDC PWM on any pin, on the real memory map.
Firmware for the modeled peripherals uses the board’s memory map. The contract also marks register addresses inside the SAR ADC and LEDC that are still unverified.
Open the board page
Arduino Uno R3
runs now
A complete ATmega328P, with three timers in every mode, USART0, the ADC, interrupts and sleep.
Blink, serial, a held button and a hardware PWM fade, at 16 MHz and real time.
Open the board page
Arduino Nano
runs now
The Uno's ATmega328P on a board 45 by 18 mm, so it pushes into the breadboard instead of standing beside it.
Two more analog inputs than an Uno, and the same firmware runs on both.
Open the board page
Arduino Mega 2560
runs now
The big Arduino: fifty-four digital pins, sixteen analog inputs and four serial ports, on the ATmega2560.
Everything an Uno sketch knows how to do, with enough pins left over to do it to twelve things at once.
Open the board page
Arduino Leonardo
runs now
An Uno-shaped board whose USB goes to the chip itself: Serial is a USB CDC endpoint and Serial1 is pins 0 and 1.
The ATmega32U4 with its ten-bit timer, fourteen ADC channels and five external interrupts, at 16 MHz.
Open the board page
ESP32-C6-DevKitC-1
runs now
A second RISC-V board: thirty-one GPIOs, 512 KB of SRAM in one window, UART0, the SYSTIMER, a twelve-bit ADC on GPIO 0 to 6 and LEDC PWM on any pin.
The contract says plainly which addresses come from the manual, which are believed rather than verified, and what is not modeled at all.
Open the board page
ESP32-S3-DevKitC-1
runs now
The ESP32-S3 on an Xtensa LX7 at 240 MHz: GPIO matrix, UART0, USB serial, ADC1, LEDC PWM and the RMT driving the RGB LED, on the real memory map.
One core where the chip has two, no radio and no FPU. Your own sketch compiles in the tab.
Open the board page
ESP8266 NodeMCU V1.0
runs now
The Xtensa LX106 at 80 MHz in the call0 ABI, with D0 to D8 that are not GPIO numbers, two active-low LEDs, and PWM done in software because the chip has none.
WiFi uses a simulated network, with no radio or real internet. The ADC is the one block whose registers are this model’s own, because Espressif never published the chip’s.
Open the board page
Raspberry Pi Pico
runs now
RP2040 on our own ARMv6-M core, with SIO GPIO, the 1 MHz timer and alarms, UART0 and eight PWM slices.
Blink, a button, serial and a fade at real time, with sleep parked on WFI.
Open the board page
Raspberry Pi Pico W
runs now
The same RP2040 and the same forty pins as the Pico, so the same ELF runs on it.
The CYW43439 is not modeled. WiFi uses a simulated network, and the on-board LED is driven through the board runtime rather than GP25.
Open the board page
Seeed XIAO SAMD21
runs now
A thumbnail-sized Cortex-M0+ at 48 MHz: eleven pads, every one of them an analog input, with PWM on ten of them.
Serial is the chip’s own USB, modeled as a byte pipe with no stack above it, and Serial1 is a real USART on D6 and D7.
Open the board page
BBC micro:bit V2
runs now
The nRF52833 on our own Cortex-M4 core at 64 MHz, with GPIO, GPIOTE, three TIMERs, RTC0 and UARTE0 on the real register map.
The 5x5 LED matrix scanned as the hardware scans it, buttons A and B, the speaker and three rings on the edge connector.
Open the board page
ATtiny85
runs now
A whole microcontroller in an 8-pin DIP, straight into the breadboard: six I/O, two timers, an ADC and a USI.
Blink, a button on INT0, a knob on the ADC and a serial port it bit-bangs for itself.
Open the board page
STM32F411 Black Pill
runs now
Cortex-M4 with Thumb-2, NVIC and SysTick at 84 MHz, with GPIO, TIM2 to TIM5 and USART1 on the real register map.
Blink on PC13, a button, serial and a PWM fade, all at real time.
Open the board page
STM32 Blue Pill (F103)
runs now
Cortex-M3 at 72 MHz, with GPIO on the F1’s CRL and CRH, TIM1 to TIM4, USART1 and a twelve-bit ADC.
Blink on PC13, a button, serial with a live reading, and a PWM fade, all at real time.
Open the board page
Arduino Uno R4 Minima
runs now
Renesas RA4M1, Arm Cortex-M4 at 48 MHz, in an Uno’s shape and on an Uno’s 5 V pins. Modeled: the PFS port block, GPT PWM on the six tilde pins, SCI2 as Serial1 on D0 and D1, and a fourteen-bit ADC that analogRead reads ten bits of.
Not modeled: a USB stack (Serial is a byte pipe with no enumeration behind it), the ICU, so there is no attachInterrupt, and the AGT. The contract says plainly which addresses come from the manual and which are believed rather than verified.
Open the board page
Arduino Pro Mini
runs now
The Uno’s ATmega328P on the smallest Arduino there is, with no USB on it, in both builds: 5 V at 16 MHz and 3.3 V at 8 MHz.
The 3.3 V board really runs at 8 MHz, so a sketch built for 16 MHz keeps half time on it, as it does on the bench.
Open the board page
Arduino Micro
runs now
The Leonardo’s ATmega32U4 on a board that pushes into a breadboard, with the L LED on pin 13 and the SPI pins on holes of their own.
Serial is the chip’s own USB and Serial1 is pins 0 and 1, and the Leonardo’s programs run on it unchanged.
Open the board page
SparkFun Pro Micro
runs now
The ATmega32U4 in a Pro Mini’s footprint with a USB socket on the end, running the Leonardo’s programs.
No LED on pin 13: its lamps are RX and TX, lit by pulling their pins low.
Open the board page
Wemos D1 mini
runs now
The NodeMCU’s ESP8266 on a board a third the size, with the same D0 to D8 names and only the holes that do something.
WiFi on a simulated network, and your own sketch compiles in the tab.
Open the board page
ESP-01S
runs now
An ESP8266 with eight pins, four of them GPIO, and a blue LED that lights when its pin is low.
Wired with jumpers, because its two rows will not sit in a breadboard. WiFi is simulated.
Open the board page
Seeed XIAO ESP32-C3
runs now
The ESP32-C3 at 160 MHz on the XIAO’s thumbnail outline: fourteen pads, and D0 to D10 that are the XIAO’s numbers, not GPIOs.
No user LED to blink, WiFi on a simulated network, and sketches that compile in the tab.
Open the board page
ESP32-C3 SuperMini
runs now
The smallest ESP32-C3 board in common use, sixteen pins named by GPIO, at 160 MHz.
Its blue LED on GPIO 8 lights when the pin is LOW, the other way around from the DevKit’s.
Open the board page
Arduino Uno R4 WiFi
runs now
The Uno R4’s RA4M1 with a 12 x 8 LED matrix to draw on through Arduino_LED_Matrix.h.
WiFi through WiFiS3.h on a simulated network: no radio, no ESP32-S3 in the model, no real internet.
Open the board page

Try it on your own firmware

What you build here runs on the board on your desk, unchanged. Nothing to install and no account needed.

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