[Oberon] Re. (2) How is ETHO with USB?

Chris Glur easlab at absamail.co.za
Sat Aug 21 14:50:07 MEST 2010

Jörg wrote:
> Huawei uses a kind of flip-flop device: First time, the USB device 
> identifies itself as a CD-ROM (see Interfaceclass in your trace, 
> SCSI mass storage), automagically installs its modem driver from
> it and that driver changes the USB type to modem.

> See detailed description here:
> http://www.draisberghof.de/usb_modeswitch/

Very interesting, but pity that the Huawei 2252+ is not mentioned.
I wasted my time investigating a friend's Huawei 2252, which had
a USB at the PC side and a RS232 at the device side of the cable.
After I bought the 2252+ I discovered that it had a usb connector
on the device and different software requirements. The device's
plastic cover has a press-out for a serial DB9 connector, and 
I'm wondering if the PCboard could take a DB9 connector, and 
run with the old-tested software, instead of buying and using

> Principally a clever idea, but this approach is highly OS dependent. 
> Seems to only work for Windows now. 
> With some USB trickery (USB_modeswitch) this can be fixed. 
> But this is not (yet??) implemented in NO/A2.


== Chris Glur.

PS. lets analyse this:
] Several new USB devices...have their MS Windows drivers 
] onboard; when plugged in for the first time they act like a 
] flash storage and start installing the driver from there.
] After that (and on every consecutive plugging) this driver 
] switches the mode internally, the storage device vanishes 
] (in most cases), and a new device (like a USB modem) 
] shows up. 
Does "first time" mean:
1. that PC saw 'such a device',
2. that PC saw THAT unique device,
3. that device saw a PC ??

Presumably the 'normal PC action' of probing the USB ports
are not over written, so the initial action, for both "first 
time" and subsequent connections, comes from the PC. So:
1. PC says 'Identify yourself';
2. device identifies itself
3. PC can confirm that it already has the driver loaded.

But if the driver is NOT loaded, the device must pretend
to be a CDROM..
? So how can the device know IF the PC has got the driver ?

The device could always ID as a CDROM and thus load & run
a utility which does:
1. have a look inside the PC & IF no driver exists 
THEN  load it from the fake-CDROM 
 ELSE talk-back to the device telling it to switch modes
   & use the existing driver.

In principle, I don't see linux allowing this.
Have these newer M$-WINs got a root/priveledged mode ?

These types of feedback loops can have unintended consequenses,
especially when one of the components is made by other parties.
My gmail often locks up - apparently at randon - because of
needing cookies ...etc. and having been designed/tested for
the mainstream browser. 
Have you read the JavaScript in many http-pages: they
always test what make of browser is 'listening', so as the
adjust what they say. What happened to universal standards!

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