Carlos, On Sunday 05 March 2006 05:23, Carlos E. R. wrote:
The Saturday 2006-03-04 at 18:07 -0800, Randall R Schulz wrote:
On Saturday 04 March 2006 17:03, Carlos E. R. wrote: ...
There is no dma for usb drives. No way.
Isn't that a function of what hardware is incorporated into the system? Are you saying that no one makes a USB adaptor with DMA capability even now that there are so many high-speed and mass storage devices? You'd think there'd be a demand for such a thing.
No, I didn't say that.
Actually, you did. You said "There is no dma for usb drives. No way."
The OP poster wanted to activate DMA for his DVD drive on the USB, the same way it is done for internal drives on the IDE bus, with hdparm or something similar.
I see.
There is no such thing.
Yes. There's (currently) no USB counterpart to "hdparm".
It should be possible for the designers of usb controller chips to use dma... but that is a diferent thing. Anyway, the speed of the bus is limited and fixed, dma would not increase it. It would lower the overhead on the cpu, that's all.
Yes and no. It's true that the use of DMA versus programmed I/O doesn't change the characteristic of the device. But if the processor has to take an interrupt for every byte (or word) transmitted, then at the upper ranges of USB bus speeds, DMA would be necessary to permit the full bandwidth of the bus to be realized without saturating the CPU. Consider the Hi-Speed USB spec. That's 20% faster than FireWire 400. Do you think any of the first-generation FireWire interfaces used programmed I/O? 40+ million interrupts per second? Doubtful.
Note:
Extracting from the wikipedia:
...
Randall Schulz