2009-05-11 04:49:16 USB HC with DMA Support

Harbhajan Singh (INDIA)

Message: 73938

Hi,

Are there any external USB host controllers drivers available with DMA Support. Please tell us in which ezkit/stamp or any platform these are available.

Thankyou.

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2009-05-11 07:23:43 Re: USB HC with DMA Support

Wolfgang Muees (GERMANY)

Message: 73946

Some USB controllers from NXP have DMA support, but you won't want it....

The only DMA support which makes sense for me for USB host controllers is busmaster DMA. Busmaster DMA is done in the PC world, and you have to search here. I think you will get some PCI chips here. So you need a Blackfin with PCI and Busmaster DMA capability.... good luck!

Non-busmaster DMA is useless because it's only a sort of memcopy inside the controller ISR. You will get no real computing time gains.

Best solution is to use a blackfin CPU with internal DMA for USB. You only have to wait about 5 years for analog devices to get their hardware up and running and adding the root hub.

regards

Wolfgang

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2009-05-11 15:38:35 Re: USB HC with DMA Support

Robin Getz (UNITED STATES)

Message: 73964

Wolfgang:

>Non-busmaster DMA is useless.

This depends on the driver & pheripheral architecture. If the driver is architected in such a way that it can take advantage of a dma_memcpy type environment - then it is far from useless. It can allow the CPU to do other things while the pheripheral buffers are being dumped to main memory. It the peripheral memory is small, then it makes little sense. If it can buffer up things - then you can see good performance gains from it.

It also has secondary benifits (on a Blackfin) - interrupts do not need to be disabled when using DMA, like they do for a core read of ASYNC space.

-Robin

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2009-05-11 23:20:09 Re: USB HC with DMA Support

liang wang (CHINA)

Message: 73974

Dear Robin:

If do not use DMA,can the usb host OHCI be realized in uclinux?If I use externel usb host IC ,but without DMA interface?

In the the field of hc_driver struct in drivers/usb/host

.urb_enqueue = ohci_urb_enqueue,

what is the effect of this function?

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