STM32F746 and External SDRAM Problem

[johnLocke]

Hello,

I want to use external SDRAM as the LTDC framebuffer with the STM32F746 microcontroller. I can write and read the desired data to/from the SDRAM without any issues. However, when I activate the LTDC, during the SDRAM initialization and configuration settings, I suddenly encounter a "target is not responding" error. After this, the microcontroller becomes completely unresponsive. The only way to recover it is to set it to boot mode and erase the entire flash memory.

What could be the problem here?

I appreciate your help.

Thank you.

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[johnLocke]

Is there anyone who can help with this issue?

[Tesla DeLorean]

Perhaps some kind of short, or issue, with pins used for video output.

Or conflicting with debug/trace pin, so PA13,PA14,PB3 to start with.

You could delay the enablement of this SDRAM/LTDC mode, say by a few seconds, this would allow for debug connectivity in a window with "connect under/after reset"

[johnLocke]

Hello, Tesla.

Thank you for your response.

The issue is not related to the conflict between LTDC pins and SWD pins or the SDRAM initialization problem. I solved the issue by connecting the BYPASS_REG pin to VDD with a resistor. Now, everything works as it should. I can write to and read from the LTDC framebuffer in the SDRAM.

My current problem, however, is that when I enter debug mode, the code runs as expected. But if I stop the debug session, I cannot reconnect to the MCU. I have to restart in boot mode and perform a mass erase on the chip. I wonder if this issue might be related to the MPU configuration.

Best regards!