Role of DMA in USB????

[prashanthaditya]

Hi all,

Can any body tell me what is the role of external DMA in any USB device??? I know that DMA interface with memory, endpoint buffers and micro controller, but how does the DMA helps in controlling memory to transfer the data and what are the signals the DMA receives to transfer the data between memory and endpoint buffers?

Please reply...

Thank you.

 

[dtn_me]

The input and output devices and their drivers expect to be able to put/get data in response to a hardware interrupt from the DMA controller when their transducer has processed one service period of data. The DMA controller can move a single sample between the device and the host buffer at a rate much faster than the sample rate of either device.

The input and output device drivers provide two service periods of system buffering. One buffer is always being processed by the DMA controller. The other buffer is guaranteed to be ready before the current buffer is exhausted.

 

[prashanthaditya]

Thank you for the reply. Could you elaborate it in detail or please tell me where can i find material relating to the above querry??

Thank you.

 

[phoenixfeng]

there are two basic types of dma: register-based
and descriptor-based
software write information(buf address, endponit number, pay-load ..etc) into register or descriptor
DMA use the information to moving data between FIFO and SDRAM

 

[archillios]

USB Controller IP ususally contain MASTER interface, for example, AHB MASTER.
Exernal DMA is a back-up, in fight with potential bugs in MASTER interface. The controller support DMA request interface of course.

Some references can be found in Mentor Graphics USB Controller IP document.