| 摘要 |
A universal serial bus (USB) device or host provides a universal serial bus (USB) controller with a direct memory access (DMA) mode. In a DMA mode, a universal serial bus (USB) transmit endpoint may be programmed for a direct memory access (DMA) transmit channel, or a universal serial bus (USB) receive endpoint may be programmed for a direct memory access (DMA) receive channel. For a USB device, a DMA transmit channel performs data transfer to a universal serial bus (USB) host, and a DMA receive channel handles data transfer from the USB host. For a USB host, a DMA transmit channel performs data transfer to the USB device, and a DMA receive channel handles data transfer from the USB device. A universal serial bus transmit protocol and a universal serial bus receive protocol for the DMA mode of the USB controller permit a maximum packet size of universal serial bus (USB) data to be programmed to a value greater than the physical size of a USB transmit or receive buffer of a USB transmit or receive endpoint. A USB controller with a DMA mode thus allows for a significant reduction in the buffer size of a USB transmit or receive buffer. A USB device having a controller with a DMA mode handles USB data as fast as the USB host can request USB data.
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