CustomBoot-32

SRA Eklavya 2025

Table of Contents

• About the Project
  • Aim
  • Description
  • Tech-Stack
  • File Structure
• Getting Started
  • Installation
• Usage
• Results and Demo
• Report
• Troubleshooting
• Contributors
• Mentors
• Resources
• Acknowledgements

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About the Project

Aim

Designing a custom PCB with OTA support and a dual-image Bootloader using ESP32 WROOM-32E and STM32F103C8T6.

Description

The project focuses on creating a custom PCB that integrates the Blue Pill (STM32F103C8T6) with ESP32 WROOM-32E.
The ESP32 hosts a website, receives two firmwares via OTA, creates memory partitions, and initializes a File System in one of the partitions.

On the STM side, a dual-image Bootloader requests firmware based on user input, verifies it, allocates it in flash memory, and executes it.
The firmware transfer is carried out via UART.

Tech-Stack

Languages & Frameworks

Libraries & Tools

Protocols & File System

File Structure

.
├── assets  # All images and test videos
│   ├── 2WayUART.mp4
│   ├── 3D-view back.png
│   ├── 3D-view.png
│   ├── EmbedC.png
│   ├── Final_PCB.png
│   ├── HAL.png
│   ├── LibOpenCM3.png
│   ├── OTA.png
│   ├── PCBSC1.png
│   ├── PCBSC2.png
│   ├── Routing.png
│   ├── SimpleBootloader.mp4
│   ├── SPIFFS.png
│   ├── UART.png
│   ├── website.png
│   ├── Wireless_CMD_Test.mp4
│   └── WorkingVideo.mp4
├── CustomBoot-32  # All the firmwares for both ESP as well as STM
│   ├── 1. OTA
│   ├── 2. Dual_Image_Bootloader
│   ├── 3. ESP_STM_UART1
│   ├── 4. ESP_STM_UART2
│   ├── 5. ESP_TO_STM_FIRMWARE_VIA_UART
│   ├── 6. ESP_STM_FILE_CRC
│   ├── 7. Controling_ESP_GPIO_Wirelessly
│   └── 8. Wireless_Firmware_Selection_ESP_STM(Additional)
├── Documentation  # Detailed documentation of the project
│   └── Final_DOC.pdf
├── Gerber files  # Files made for fabrication of PCB  
├── README.md
└── Schematic files  # Schematics of our PCB
    ├── 4 SRA.kicad_pcb
    └── 4 SRA.kicad_sch

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Getting Started

Installation

1. Clone the repo

   git clone https://github.com/avm1234567/Customboot-32.git

2. Navigate to the project directory

   cd CustomBoot-32

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Usage

The codes used in our project are in the CustomBoot-32 directory.

1. OTA

• From the CustomBoot-32 directory, navigate to the OTA directory:

cd CustomBoot-32/1.\ OTA

• In the code, set your Wi-Fi SSID and password (lines 16-17):

#define WIFI_SSID "Your_SSID"
#define WIFI_PASS "Your_Password"

• Build using ESP-IDF PowerShell:

idf.py fullclean
idf.py build

• Flash and open the serial monitor:

idf.py flash monitor 

2. Dual_Image_Bootloader

• To generate the binary files, open this project in STM32CubeIDE and build it.
• To flash this code, use STM32CubeProgrammer:
  1. Flash LED_BLINK_2.bin at start address 0x08006000: CustomBoot-32/2. Dual_Image_Bootloader/LED_BLINK_2/Debug/LED_BLINK_2.bin
  2. Flash LED_BLINK.bin at start address 0x08004000: CustomBoot-32/2. Dual_Image_Bootloader/LED_BLINK/Debug/LED_BLINK.bin
  3. Flash the Bootloader at start address 0x08000000: CustomBoot-32/2. Dual_Image_Bootloader/Learning_Bootloader/Debug/Learning_Bootloader.bin
• Click Start Programming to run.

3. ESP_STM_UART1

• For the ESP32 code:

cd CustomBoot-32/3.\ ESP_STM_UART1/ESP_STM_COMM
idf.py fullclean
idf.py build
idf.py flash monitor 

• For the STM32 code, generate build files in STM32CubeIDE and flash the binary using STM32CubeProgrammer at address 0x08000000.

4. ESP_STM_UART2

• For the ESP32 code:

cd CustomBoot-32/4.\ ESP_STM_UART2/ESP_STM_COMM
idf.py fullclean
idf.py build
idf.py flash monitor 

• For the STM32 code, generate build files in STM32CubeIDE and flash the binary using STM32CubeProgrammer at address 0x08000000.

5. ESP_TO_STM_FIRMWARE_VIA_UART

• For the ESP32 code:

cd CustomBoot-32/5.\ ESP_TO_STM_FIRMWARE_VIA_UART/OTA
idf.py build
idf.py flash monitor 

• For the STM32 code, build in STM32CubeIDE and flash the binary found at CustomBoot-32/5. ESP_TO_STM_FIRMWARE_VIA_UART/Learning_Bootloader/Debug/Learning_Bootloader.bin at address 0x08000000.

6. ESP_STM_FILE_CRC

• Clone libopencm3 required for the bootloader:

git clone https://github.com/libopencm3/libopencm3.git
cd libopencm3

• Flash the ESP32 firmware:

cd CustomBoot-32/6.\ ESP_STM_FILE_CRC/OTA
idf.py fullclean
idf.py build flash monitor

7. Controlling_ESP_GPIO_Wirelessly

• Clean, build, and flash:

cd CustomBoot-32/7.\ Controling_ESP_GPIO_Wirelessly
idf.py fullclean
idf.py build
idf.py flash monitor

8. Wireless_Firmware_Selection

• Clone libopencm3 required for the bootloader:

git clone https://github.com/libopencm3/libopencm3.git
cd libopencm3

• Flash the ESP32 firmware:

cd CustomBoot-32/8.\ Wireless_Firmware_Selection_ESP_STM\(Additional\)/OTA
idf.py fullclean
idf.py build flash monitor

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Results

Custom PCB Views:

Front	Back

Demo

Working Demo of Final PCB

For other results and test videos, check the Google Drive Folder.

Report

Refer to the detailed project Report.

Troubleshooting

• ERC rule check errors in PCB schematics.
• Routing issues in compact areas while adhering to manufacturer constraints.
• Wi-Fi SSID and password options not appearing in Menuconfig.
• CMakeLists errors affecting SPIFFS initialization.
• Partition table not being detected.
• SPIFFS initialization failure at runtime.
• Favicon loading errors.
• OTA binaries containing unnecessary bloatware.
• UART initialization issues.
• Binary file transfer failures.
• Errors in custom file protocol implementation.
• End-byte transmission errors during communication.
• Application jump not functioning correctly (MSP not set).
• Correct HAL-like application jump with LibOpenCM3.
• Schematic issues resolved through perfboard prototyping and testing.

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Contributors

• Varun Patil
• Omkar Nanajkar
• Archit More

Mentors

• Prithvi Tambewagh
• Shaunak Datar
• Vishal Mutha

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Resources

• Bootloader basics (EmbeTronicx)
• EmbeddedInventor: Bootloader
• Getting Started with STM32
• Bare-metal UART STM32
• ESP32 UART
• CRC32 for STM
• LibOpenCM3 documentation
• SPIFFS
• FreeRTOS
• ESP Web Server Handling
• File Transfer Protocols

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Acknowledgements

We are extremely grateful to our mentors – Prithvi Tambewagh, Shaunak Datar, and Vishal Mutha – for their guidance and support throughout the course of this project.

We also thank SRA-VJTI for their support in organizing Eklavya 2025 and for providing us the opportunity to work on this project.