Although the buffer descriptor table is located inside the packet buffer memory, its entries can be considered as additional registers used to configure the location and size of the packet buffers used to exchange data between the USB macro cell and the STM32F10xxx. Due to the common APB bridge limitation on word addressability, all packet memory locations are accessed by the APB using 32-bit aligned addresses, instead of the actual memory location addresses utilized by the USB peripheral for the USB_BTABLE register and buffer description table locations.
相关链接:http://www.st.com/stonline/products/literature/rm/13902.pdf
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