Bare-Metal CAN 2.0 Network with Custom Error-Correcting Code (ECC)

Overview

A bare-metal implementation of the Controller Area Network (CAN 2.0B) protocol.

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Hardware Architecture

• Node 1: ESP32
• Node 2: TI TM4C123GH6PM
• Physical Layer: 2x TI SN65HVD230 (VP230) 3.3V CAN Transceivers

Interconnect & Pin Mapping

Signal	TM4C123 (CAN0)	VP230 #1	VP230 #2	ESP32 (TWAI)	Notes
VCC	+3.3V	3.3V	3.3V	3V3	Native 3.3V logic levels
GND	GND	GND	GND	GND	Common ground reference required across nodes
CANTX	PB5 (CAN0Tx)	CTX	CTX	GPIO 21	Routed via GPIO Matrix (ESP32) / PCTL Mux 0x8 (TM4C)
CANRX	PB4 (CAN0Rx)	CRX	CRX	GPIO 22	Routed via GPIO Matrix (ESP32) / PCTL Mux 0x8 (TM4C)
CAN_H	—	CANH	CANH	—	$120\ \Omega$ termination enabled on both endpoints ($60\ \Omega$ nominal)
CAN_L	—	CANL	CANL	—	Differential pair

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Repository Structure

├── ESP32/CAN/       # ESP-IDF v6.1 CMake project (TWAI direct register access)
└── TM4C123/         # Keil uVision MDK-ARM project (C_CAN bare-metal)

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Toolchain & Build Setup

1. ESP32 Node (VS Code + ESP-IDF v6.1)

1. Install the ESP-IDF extension in VS Code and run ESP-IDF: Open ESP-IDF Installation Manager[cite: 3].
2. Provision the toolchain via Easy Installation (installs Xtensa GCC, CMake, Ninja, and ESP-IDF v6.1 to the host environment)[cite: 3, 5].
3. Reload the window (Developer: Reload Window) and generate a blank project in ESP32/CAN via ESP-IDF: New Project (template-app)[cite: 4].
4. Open ESP32/CAN as the workspace root so CMake and clangd resolve compile_commands.json[cite: 4, 5].
5. Set target architecture to esp32, build the project to index register headers (soc/twai_struct.h), and flash via UART[cite: 5].

2. TM4C123 Node (Keil uVision MDK-ARM)

1. Install the Keil::TM4C_DFP device family pack via Pack Installer.
2. Create a new project in TM4C123/ targeting TM4C123GH6PM.
3. In the Run-Time Environment (RTE) manager, include only CMSIS::CORE and Device::Startup (startup_TM4C123.s and system_TM4C123.c—no peripheral driver libraries).
4. Set the debug and flash probe to Stellaris ICDI under Target Options $\rightarrow$ Debug / Utilities.

The extra files and whatever that need to be downloaded to set up the board were stolen from Quantum Leaps - Modern Embedded Systems Programming series so god knows how to set everything up again. Good luck.

My Notes

ESP32 Stuff

These milestones were generated by Gemini, that's my guide, and then I am making notes on everything as a reference for future use since Gemini yaps too much.

Milestone 1: Wake Up the Silicon (Clock & Reset)

To save power, most peripherals are disabled and held in a reset state by default upon boot.

Clock: Digital logic circuits require an oscillating clock signal to step through operations and move data across registers.

Reset: The reset line forces all internal state machines, FIFOs, and registers of a specific peripheral back to their default hardware values without rebooting the entire CPU. By setting DPORT_PERIP_RST_EN_REG to 0, we are leaving this reset mode, letting it operate.

Milestone 2: Routing Pins Through the GPIO Matrix

First, some mapping magic happens.

Second, we need to output enable the GPIO pins.

Use GPIO.enable_w1ts = (1 << PIN_NUM)

• enable (Direct Read/Write): Writing to this register overwrites all 32 pins at once.

• enable_w1ts (Write 1 to Set): Writing a 1 to any bit position turns on output enable for that corresponding GPIO pin, while writing a 0 does nothing and leaves existing pins completely untouched.

• enable_w1tc (Write 1 to Clear): Writing a 1 to any bit position turns off the output enable for that corresponding GPIO pin.

CANTX is the output from the ESP32. CANRX is the input from the ESP32.

TWAI_RX_IDX = 94

TWAI_TX_IDX = 123

Then lastly you need to map the GPIO pin to the right index

GPIO.func_out_sel_cfg[21].func_sel = 123; // Set GPIO21 to output the CAN TX signal (index 123)

Milestone 3: Configure the TWAI Registers (While in Reset Mode)

Reset Mode is a state where the controller is electrically and logically disconnected from the TWAI bus.

Firstly, we enter reset mode and also enter extended mode.

Extended Mode switches the TWAI hardware from a 1980s legacy register layout (Basic Mode / BasicCAN) to the modern CAN 2.0B register architecture.

Then, we want to configure our BAUD rate. Use TWAI_BUS_TIMING_0_REG and TWAI_BUS_TIMING_1_REG.

For 0_REG, we can configure the BAUD rate (TWAI_BAUD_PRESC) and the Synchronization Jump Width. Need to find out what exactly the jump width is later.

For 1_REG, we can configure some other things, but more interestingly, the sample method! In this project we chose triple sampling (bus_timing_1_reg.sam = 1).

And then we want to configure the acceptance filters.

Lastly, we can send a packet!!

Use tx_rx_buffer[].byte.

TM4C123 Stuff

RX - PB4 and TX - PB5

PB4 and PB5 are wired strictly to CAN0Rx and CAN0Tx (Module 0).

Milestone 1: Clocks & GPIO Pin Muxing

Woke up the CAN0 hardware and connected it physically to pins PB4 and PB5 on the chip.

Milestone 2: CAN Initialization & 500 kbps Bit Timing

Use same values as ESP32.

Milestone 3: Configure Message Object 1 as a Receiver (via IF1 or IF2)

Milestone 4: Poll for New Data and Read the Byte

General

To turn on a bit, use "|=", and to turn it off, use "&= ~".