[Feedback] USB Setup buffer should be separated from PCD_HandleTypeDef structure

[lconlcong]

Description

Currently, in the HAL USB driver, the PCD_HandleTypeDef structure embeds the setup packet buffer directly:

uint32_t Setup[12]; /*!< Setup packet buffer */

This design tightly couples the control structure (state, locks, callbacks) with a DMA-dependent buffer. As a result:

• When USB OTG FS/HS DMA is enabled, the entire PCD_HandleTypeDef must be located in a DMA-accessible SRAM region.

• This prevents developers from keeping the handle itself in faster memory (e.g. DTCM) while only placing the setup buffer in SRAM.

• It reduces flexibility and forces a performance compromise.

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Suggestion

The setup buffer should be separated from the handle:

• PCD_HandleTypeDef should only store a pointer to the setup buffer.

• The actual buffer can then be allocated by the user in a proper memory region (DMA-accessible SRAM).

For example:

uint32_t *Setup; /*!< Pointer to setup packet buffer */

This would make memory placement more flexible:

• Developers can keep the handle in DTCM for fast CPU access.

• Only the setup buffer needs to be placed in SRAM for DMA.

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Current Workaround

The current workaround is to move the entire handle into SRAM, but this is suboptimal because most fields in the handle do not require DMA access.