Alan,
>
> On Thu, 4 Jan 2007, Mike King wrote:
>
> > > > > > Anytime a SET_CONFIGURATION is sent to the device without being
> > > > > > preceeded
> > > > > > by the secret vendor specific command the device reverts to the
> > > > > > previous
> > > > > > device descriptor data indicating 100ma.
>
> When you say "preceeded by", do you mean "immediately preceeded by"? How
> long a time, and what other requests, are allowed to come between the
> secret command and the Set-Config? What if there are two consecutive
> Set-Configs -- will the second one cause the device to revert?
What I see with the analyzer is that the secret command immediately preceeds
the set-config. And, yes, a second set-config causes the device to
restore the power-on default device descriptor indicating 100ma.
>
> BTW, it's very unusual -- bordering on illegal -- for a device to change
> the contents of its configuration descriptor without re-enumerating. Are
> you sure it really does this? Or does it leave the descriptor the same
> (500 mA) but revert to drawing only 100 mA of current?
I'm sure it does this as I'm watching with a hardware analyzer (Finisar
Bus Doctor). In terms of actual current draw, I don't know. I don't have
a current probe to see what is happening. I do know that on the display
it will say "insufficient charging current" if it has not gone thru this
secret command / set-config sequence.
>
>
> > > The settling time is only necessary after the secret command and the
> > > SET_CONFIGURATION. The device resets itself and is coming out of reset
>
> Note: You say the device "resets" itself, but you really mean that it
> disconnects itself from the USB bus and then reconnects. That's different
> from a reset.
Thanks for correcting me. I am still trying to teach myself about USB
devices as well as the Linux USB implementation. What the analyzer indicates
is a reset. Here is the full sequence as shown by the Finisar :
GET_DESCRIPTOR DEVICE
SET_ADDRESS
GET_DESCRIPTOR DEVICE
GET_DESCRIPTOR CONFIG (9 bytes)
bMaxPower = 100ma
0x09 0x02 0x2e 0x00 0x01 0x01 0x00 0x80 0x32
GET_DESCRIPTOR CONFIG (full config)
GET_DESCRIPTOR STRING (repeated 4 times with different indexes)
CLASS_SPECIFIC CMD (secret command) value=0, index=1, length=0
SET_CONFIGURATION config value = 1,index=0,length=0
reset
reset
reset
GET_DESCRIPTOR DEVICE
SET_ADDRESS
GET_DESCRIPTOR DEVICE
GET_DESCRIPTOR CONFIG (9 bytes)
bMaxPower = 500ma, all other settings are same as previous
0x09 0x02 0x2e 0x00 0x01 0x01 0x00 0x80 0xfa
GET_DESCRIPTOR CONFIG (full config)
GET_DESCRIPTOR STRING (repeated 4 times with different indexes)
SET_CONFIGURATION config value = 1, index=0,length=0
BULK
BULK
BULK
...
...
... ad infinitum
>
> > Hi,
> >
> > maybe I am dense. On Windows you see:
> >
> > secret command -> SET_CONFIGURATION -> {device resets by itself} ->
> > SET_CONFIGURATION >> 500 mA
> >
> > don't you? If so, I am suggesting you do:
> >
> > secret command -> usb_reset_device() -> {device is reset by the hub} ->
> > SET_CONFIGURATION (from normal probe)
> >
> > I am speculating that the device firmware has code like:
> >
> > switch (command) {
> > case SECRET_COMMAND:
> > reset_upon_set_config = 1;
> > full_power = 1;
> > break;
> > case SET_CONFIGURATION:
> > if (reset_upon_set_config) {
> > reset();
> > } else {
> > set_config();
> > }
> >
> > So it might not matter how the reset is done.
>
> When is full_power cleared? If it gets cleared at the end of the
> SET_CONFIGURATION case then you will have the following sequence:
>
> secret command (reset_upon_set_config = full_power = 1)
>
> Set Configuration (Does a disconnect & reset, turns on full power
> mode, and does reset_upon_set_config = full_power = 0)
>
> Re-enumerate (Reads 500 mA power usage in the new descriptor)
>
> Device recharges its battery but is unusable because it is in
> the unconfigured state
>
> Set Configuration (Now the device is usable but it has reverted
> to 100 mA since full_power was 0)
>
> This doesn't seem to square with what Mike wrote earlier.
>
> You should note also that in this situation it won't help to call
> usb_reset_device() from the probe routine. You still won't be able to
> avoid the Set Configuration request after the reset completes.
Full power is never cleared. The device stays in this state as long as
it is connected.
>
> Alan Stern
>
Thanks,
Mike
P.S. Alan, I also forgot to thank you for a previous response to my question
"Are endpoint addresses unique". Many thanks for that response as well.
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