Re: [Libusb-devel] How to read reports with libusb

[lpx <sin...@ho...>]

Hi,

I have tried to change the class value to 0xFF but it brought me problems.

Before the change the device appeared to the system as a joystick, and after
the change it was not being found as a joystick.

Nuno


Tim Roberts wrote:
> 
> lpx wrote:
>> -> You shouldn't declare yourself as device class 0.  That has a specific
>> meaning -- it means you are a composite device, which this device is
>> not.  The "vendor-defined" device class is 0xff, and that's what you
>> should use.
>>
>> I didnt made this device descriptor. I'm just using it. Thx for the
>> corrections. 
>>   
> 
> I thought this was a device you were building.
> 
>> Can you tell me something? 
>>
>> Why should it be a vendor-defined instead of composite?
>>   
> 
> By declaring the device class as one of the known values, you are
> promising that your device follows the USB specification for that
> class.  A composite device acts like a USB hub.  It means you have
> several different interfaces, each of which can be treated
> independently.  For example, USB cameras are often composite devices,
> with an audio interface and a video interface inside.
> 
> The problem with declaring yourself as a composite is that the operating
> system believes it knows how to talk to a composite device, by treating
> it like a USB hub.  If you plug your device into Windows, for example,
> the operating system will assign the USB hub driver to your device
> automatically.
> 
> If you don't act like one of the pre-defined device classes, then you
> must declare yourself as vendor-defined.  USB devices must follow the
> rules in the USB specifications.  It would be more accurate to declare
> your device as being in the HID class, if that's the model you intend to
> use.
> 
>> -> If you want 8 bytes, why did you try to read 60 bytes?
>>
>> You are right! I don't want to read 8 but 60 which is the length of the
>> report. Another mistake!
>>   
> 
> 60 is the length of the report DESCRIPTOR, not the report.  This is a
> very important distinction.  The report descriptor tells you how long
> the reports will be.
> 
>> Can you telll me one more thing?
>>
>> Why does the executable of libusb program look like a shell script? That
>> is
>> very weird! And if i want to use libusb to access USB devices into
>> complex
>> programs, they cannot look like a sheel script... What is going on? 
>>   
> 
> libusb is not a program, it is a library that gets linked in to your own
> programs.  All Unix libraries start out with the text string
> "!<arch>\n".  This is just how the "ar" program identifies its
> products.  If you do "file libusb.a", you will clearly see that it is
> not mistaken for a shell script.
> 
> -- 
> Tim Roberts, ti...@pr...
> Providenza & Boekelheide, Inc.
> 
> 
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