usb problem in a embedded system

Jun 12, 2007 3 Replies
M

Hi,



I'm developing an embedded system which can work as an USB host. It i based on the PIC18F6622 mcu, and the MAX3421E USB driver. While working as USB host, the system should communicate to any flas memory stick. At the moment, I've tried 4 different memory sticks, and just 2 of the work fine, so it is possible to read/write files from/to them (all devices work fine when plugged to a PC). The 2 devices that do not work report to the SCSI comman "test_unit_ready" with 0x01, that is, they are not ready. I don't know how to make them be ready. I've tried to reset them, but the always report the same. Any suggestion?



Thanks


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L

It is a matter of breathtaking complexity to support "standard" products from different vendors. The best advice one can give is to observe exactly what happens when you plug those sticks into a Windows host, and emulate what you see there.

Are these perhaps password-protected?

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M

I dont think they are password protected as in XP you dont need a OEM driver for it, they just work under the XP operating system.

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A

Do you mean that the returned CSW contains 0x01 ("Command failure")? If so, you need to read the sense (REQUEST_SENSE) from the stick to find out what it is objecting to. This will give you the sense code as well as the additional sense codes. Have you checked what class/subclass/protocol the sticks are returning - are they all the same?

Andrew

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