USB HS CDC stop working if Internal IP DMA is enabled on STM32F469NI

[kiran_g]

Hi,

I am working on STM32F469NI using the USB OTG HS peripheral in CDC (VCOM) mode.

• When using USB CDC without DMA, the VCOM works fine.

• However, when I enable Internal IP DMA (from CubeMX → USB_OTG_HS → Parameter Settings → Enable internal IP DMA), the USB CDC communication stops working after some time.

Setup details:

• MCU: STM32F469NI

• USB mode: Device (CDC VCOM)

• PHY: Internal FS PHY

• DMA Mode: Internal IP DMA enabled for USB_OTG_HS

• Running on custom board

Observed behavior:

• On PC, the VCOM port is detected correctly.

• Initially, data transfer works fine.

• After some time (or after repeated Tx/Rx), the communication hangs completely. No data transfer occurs until reset.

• If I disable Internal IP DMA, the issue goes away.

What I tried:

• Checked buffer alignment (made Tx buffers 4-byte aligned).

• Verified HAL callbacks (CDC_Transmit_FS etc.) are still being called.

Questions:

1. Is Internal IP DMA for USB HS CDC fully supported on STM32F469NI?

2. Are there known limitations / errata related to this?

3. Any additional configuration needed for DMA mode (buffer alignment, cache maintenance, etc.)?

4. Could this be an issue in Cube/HAL implementation?

Any guidance or reference examples would be helpful.