On Wednesday 16 March 2005 10:29 am, Dan Ingalls wrote:
> Ned Konz <ned at squeakland.org>  wrote:
> >And MIDI?
>
> This makes me think of more areas where we need nice cross-platform
> support.  Namely
>
>  USB
> and
>  BlueTooth.
>
> Has anyone given some thought to how we might pull all these facilities
> together in a nice uniform manner and then provide necessary VM support so
> that it is wonderfully independent of platform?
>

One problem is that USB doesn't generally present itself as a generic serial 
stream (unless you're using a USB to serial converter, in which case it looks 
like a standard serial port).

Instead, USB devices have different kinds of interface depending on their 
device class -- HID (human interface devices), Storage, etc.

-----
From the USB organization web site:

Device Descriptor bDeviceClass values:

Value Hex Value Descriptor
0  0  Class information at interface level
2  2  Communication (or with WMC 1.0 class information at interface level)
9  9  HUB
220  DC Diagnostic Device (see below for details)
224  E0  Wireless Controller (see below for details)
239  EF  Miscellaneous Device Class (see below for details)
255  FF  Vendor-Specific

Interface Descriptor bInterfaceClass values:

Value Hex Value Descriptor
1  1  Audio
2  2  CDC-Control
3  3  HID
5  5  Physical
6  6  Image (subclass & protocol must be 1)
7  7  Printer
8  8  Mass-Storage
9  9  HUB
10  A  CDC-Data
11  B  Chip/Smart Card
13  D Content-Security
14  E  Video
220  DC  Diagnostic Device (see below for details)
224  E0  Wireless Controller (see below for details)
254  FE  Application-Specific (see below for details)
255  FF  Vendor-Specific

Device / Interface Class Code Details:

Diagnostic Device (Device/Interface Class Code 220)
SubClass        Protocol
1  Reprogrammable Diagnostic Device  1  USB2 Compliance Device
 
Wireless Controller (Device/Interface Class Code 224)
SubClass        Protocol
1  RF Controller       1  Bluetooth Programming Interface

Miscellaneous Device Class (Device Class 239)
SubClass         Protocol
2  Common Class      1  Interface Association Descriptor

Application-Specific (Interface Class Code 254)
SubClass
1  Device Firmware Update
2  IrDA Bridge
3  Test & Measurement Class (USBTMC)

-----

And then there's the vendor-specific definitions (like, for instance, a number 
of the scanners and USB/serial interfaces), where the protocol isn't even 
predictable.

And the way in which the various operating systems expose these APIs varies 
considerably.

On some systems, for instance, if you plug in a USB CD drive you won't be able 
to talk to it via the more generic USB interface, as that interface will be 
owned by the storage driver.

On Linux, there's a userland USB host interface (usbdevice_fs.h) and a USB 
client interface (for computers that are USB slaves) (usb_gadgetfs.h).  The 
USB host interface includes these ioctl calls:

USBDEVFS_CONTROL         
USBDEVFS_BULK            
USBDEVFS_RESETEP         
USBDEVFS_SETINTERFACE    
USBDEVFS_SETCONFIGURATION
USBDEVFS_GETDRIVER       
USBDEVFS_SUBMITURB       
USBDEVFS_DISCARDURB      
USBDEVFS_REAPURB         
USBDEVFS_REAPURBNDELAY   
USBDEVFS_DISCSIGNAL      
USBDEVFS_CLAIMINTERFACE  
USBDEVFS_RELEASEINTERFACE
USBDEVFS_CONNECTINFO     
USBDEVFS_IOCTL           
USBDEVFS_HUB_PORTINFO    
USBDEVFS_RESET           
USBDEVFS_CLEAR_HALT      
USBDEVFS_DISCONNECT      
USBDEVFS_CONNECT         

Are there particular devices or types of devices that you'd like to interface 
to?

I'm not sure about Bluetooth; where I've seen it used it's looked like a 
serial connection, but with the identity of the two ends known (so there's 
potentially a bit of "pairing" and enumeration protocol involved).

-- 
Ned Konz
http://bike-nomad.com/squeak/