On 6/2/06, Xiaofan Chen wrote: > I just came across an interesting thread in the linux-usb-devel mailing > list. > http://marc.theaimsgroup.com/?l=linux-kernel&m=114915375324284&w=2 > > The main problem is that lots of USB device does not follow the USB > specification in terms of power budget and it is now up to the Linux > USB developers to decide how to deal with them. > > I think we will also meet this kind of problems during design. What > will you do in this case? > In some cases, depending on the customer we would suggest them to buy qualified parts or we can even supply the parts as an accessory. For example, sensor manufacturers normally will supply the cord sets, mounting brackets and other accessories and they can be good business. The best (or worst to us consumers) example is the InkJet Printer industry. Sometime we can just say sorry to the customer --> you pay what you get. In this particular case, it is obviously not possible since the Linux developers are not really selling something even though we could consider the Linux users to be their customers. I actually agree with Alan Stern (the Linux USB developer who comes out the patch). At most Linux should only allow a bit over current. To allow 200mA where 100mA is the requirement is a really too much since the consumer USB port are not really that robust to handle this. The flash memory makers should fix the problems and the average users should use better quality USB sticks. In some other cases, I would try to fulfill the customer's requirement but there should be a limit that the quality/reliability of the product should not be compromised. That is why often we need to give quite some reserves within the design limit (technical limit and cost limit). It is sad to hear cheap computer casings (with no proper ground of the USB port) can kill some very expensive gadgets or some very cheap USB lamps/fans could kill the computer motherboards. Regards, Xiaofan -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist