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STM32L496 firmware >512 KB - dual-bank flash overlap (normal execution + OTA)

Taksh
Associate III

‎2026-01-29 4:35 AM - last edited on ‎2026-01-29 5:08 AM by

Hello ST Community,

I am working on an OTA firmware update implementation on STM32L496, and I am facing an issue related to dual-bank internal flash usage when the firmware size exceeds 512 KB.
I would like to explain my setup and the problem in a simple and clear way.

 

MCU and Flash Details

  • MCU: STM32L496

  • Internal Flash: 1 MB

  • Flash configured in dual-bank mode

    • Bank1: 512 KB

    • Bank2: 512 KB

 

What We Are Doing

Normal Application

  • The main application is stored in internal flash

  • Firmware is built using STM32CubeIDE

  • No OTA activity during normal operation

OTA (Current / Tested)

  • OTA is performed using NB-IoT and NFC

  • Firmware is received in chunks

  • Chunks are written to flash

  • CRC is verified

  • After successful verification, firmware is switched

This OTA flow works only when firmware size is less than 512 KB.

 

Main Issue (Occurs Even Without OTA)

When the firmware size increases beyond 512 KB (for example ~600 KB), the system starts misbehaving even if OTA is not started at all.

Observed Behavior

  • UART logs show garbage or corrupted values

  • Application does not work as expected

  • Random or unstable behavior is observed

Important Point

This happens:

  • Without erasing flash

  • Without writing flash

  • Without switching banks

  • During normal execution only

When firmware size is below 512 KB, the system works perfectly.

 

Our Understanding of the Problem

  • When firmware size is less than 512 KB, the entire code fits in Bank1

  • When firmware size exceeds 512 KB:

    • The linker places code and data in both Bank1 and Bank2

    • The application executes across both banks

According to documentation, executing code from both banks should be supported.
However, in our case, once the code spans Bank1 and Bank2, instability is observed.

 

Why This Is Important for OTA

We are planning to move OTA storage to external SPI flash (MX25R3235F, 4 MB) and use a bootloader-based OTA approach.

However, even with external flash OTA:

  • The application firmware itself will still be larger than 512 KB

  • If execution across Bank1 + Bank2 is not reliable, external OTA will also not work

So the first priority is to understand and solve this dual-bank execution issue for large firmware.

 

Questions

  1. Is it fully supported to run a single application spanning Bank1 and Bank2 on STM32L496?

  2. Are there any specific option byte settings required for firmware larger than 512 KB?

  3. Are there any known limitations or errata related to large firmware on STM32L4 series?

  4. Are there any recommended linker script examples from ST for applications larger than one bank?

 

Summary

  • Firmware <512 KB → works correctly

  • Firmware >512 KB → unstable behavior

  • Issue occurs even without OTA

  • OTA (internal or external) depends on resolving this first

Any guidance, confirmation, or reference from the community would be very helpful.

Thank you for your time and support.

Best regards,
Taksh Patel

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TDK
Super User

‎2026-01-29 6:06 AM

Some STM32L496 chips only have 512 kB of FLASH. Which one are you using?

After updating, verify the content of the flash using STM32CubeProgrammer. If it matches what is expected, there is no issue with the update procedure.

There is no inherent problem or restriction with an application using both banks. Probably your OTA isn't working correctly here.

If you feel a post has answered your question, please click "Accept as Solution".
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