You want to a guess what the MaxPower is listed for the Logitech V20 portable
usb speakers are that are plugged into my pc?
I'll give you one guess.
Yep, MaxPower is listed as 590 mA
"The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire to
power connected USB devices.
A unit load is defined as 100 mA in USB 2.0, and 150 mA in USB 3.0. A device
may draw a maximum of 5 unit loads (500 mA) from a port in USB 2.0; 6 (900 mA)
in USB 3.0."
"Bus 003 Device 002: ID 046d:0a04 Logitech, Inc. V20 portable speakers (USB
powered)
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 1.10
bDeviceClass 0
bDeviceSubClass 0
bDeviceProtocol 0
bMaxPacketSize0 8
idVendor 0x046d Logitech, Inc.
idProduct 0x0a04 V20 portable speakers (USB powered)
bcdDevice 0.07
iManufacturer 1 Logitech
iProduct 2 Logitech USB Speaker
iSerial 0
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 0x00e9
bNumInterfaces 3
bConfigurationValue 1
iConfiguration 3 G6 2005/03/29 10:05
bmAttributes 0xc0
Self Powered
MaxPower 500mA
The total RMS Power of the Logitech V20 Portable USB Speakers = 2 W or 2000 mA.
Whether I'm driving audio through the speakers our not, the MaxPower stays at
500 mA.
LSUSB MaxPower is the power output of the USB port the USB device is connected
to and not what that MaxPower of the device is or can take.
All the USB ports on my pc are 2.0, if you've a mix of USB ports or different
PCs with different USB port specs, you can prove this by moving the USB device
to the different ports and checking the MaxPower that LSUSB lists.
Sent with Proton Mail secure email.
------- Original Message -------
On Tuesday, January 17th, 2023 at 2:59 PM, Galen Seitz <[email protected]>
wrote:
> On 1/17/23 14:48, MC_Sequoia wrote:
> ...snip...
>
> > So, in conclusion I think the "MaxPower" data point provided by lsusb
> > command is about the bus electrical output capacity that the device
> > is connected to and not about the device itself that's connected to
> > the usb bus.
>
>
> This is not true, at least not for a USB device (not a hub). The
> MaxPower descriptor contains the maximum current that the device will
> ever draw. Properly designed USB devices first come up in a low power
> state where they draw 100 mA or less. The software driving the USB
> system calculates how much power is available. If there is sufficient
> power available, then the system initializes the device and allows it to
> go to its desired higher power state.
>
>
> galen
> --
> Galen Seitz
> [email protected]
