Raghavendra wrote: > I have a query regarding DMA(Direct Memory Access) for the usb devices. USB devices never do DMA. > As far as Linux is concerned, how the DMA action being taking place for > USB devices. It doesn't take place. > As per my understanding, the USB host controller is taking care of > the DMA operations. That's correct. When an URB is submitted by host software the host controller asks the device for data, and when data arrives from the device the host controller writes the data into memory using DMA. > But I require a little more insight into it. I recommend to study chapters 5 and 8 of the USB 2.0 specification: http://www.usb.org/developers/docs/usb_20_070113.zip > Further more, if it is possible for the USB devices, then can this > support be also extended towards low-end protocols such as I2C or SPI? Not in the general case. It is possible to develop an I²C or SPI bus master which is capable of DMA toward the host memory, and to create a protocol on top of I²C or SPI which allows devices to remote control the DMA engine in the master, but I'd say that's quite an artificial case. //Peter -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
