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Control the power state of USB devices and ports on your testbed using USB hubs with per-port power control.

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Import

from lager import Net, NetType

# For exception handling
from lager import (
    USBBackendError,
    LibraryMissingError,
    DeviceNotFoundError,
    PortStateError
)

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Methods

MethodDescription
enable()Enable (power on) USB port
disable()Disable (power off) USB port
toggle()Toggle USB port power state; returns the resulting state (True=enabled)
state()Read the current power state without changing it (True=enabled)

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Exception Classes

ExceptionDescription
USBBackendErrorBase class for USB hub errors
LibraryMissingErrorRequired vendor SDK not installed
DeviceNotFoundErrorUSB hub not found
PortStateErrorError changing port state

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Method Reference

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Net.get(name, type=NetType.Usb)

Get a USB net by name. 
from lager import Net, NetType

usb = Net.get('DUT_USB', type=NetType.Usb)
Parameters:
ParameterTypeDescription
namestrName of the USB net
typeNetTypeMust be NetType.Usb
Returns: USB Net instance

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enable()

Enable (power on) the USB port. 
from lager import Net, NetType

usb = Net.get('CAMERA_USB', type=NetType.Usb)
usb.enable()
print("USB port powered on")

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disable()

Disable (power off) the USB port. 
from lager import Net, NetType

usb = Net.get('CAMERA_USB', type=NetType.Usb)
usb.disable()
print("USB port powered off")

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toggle()

Toggle the power state of the USB port. Returns the resulting state (True if now enabled, False if now disabled). 
from lager import Net, NetType

usb = Net.get('SENSOR_USB', type=NetType.Usb)
now_on = usb.toggle()  # On -> Off or Off -> On

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state()

Read the current power state of the USB port without changing it. Returns True if the port is currently enabled (powered on), False if disabled. The value is read live from the hub, so it always reflects the real port state. 
from lager import Net, NetType

usb = Net.get('SENSOR_USB', type=NetType.Usb)
if not usb.state():
    usb.enable()   # only power on if it isn't already

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Examples

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Basic Power Control

from lager import Net, NetType

# Get USB net
usb = Net.get('CAMERA', type=NetType.Usb)

# Power on USB device
usb.enable()
print("Camera powered on")

# Power off USB device
usb.disable()
print("Camera powered off")

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Power Cycle Device

from lager import Net, NetType
import time

def power_cycle(net_name, delay=2):
    """Power cycle a USB device."""
    usb = Net.get(net_name, type=NetType.Usb)
    print(f"Power cycling {net_name}...")
    usb.disable()
    time.sleep(delay)
    usb.enable()
    print(f"{net_name} restarted")

power_cycle('DUT_USB')

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Error Handling

from lager import Net, NetType
from lager import (
    USBBackendError,
    LibraryMissingError,
    DeviceNotFoundError,
    PortStateError
)

try:
    usb = Net.get('SENSOR_USB', type=NetType.Usb)
    usb.enable()
    print("Sensor powered on")

except LibraryMissingError:
    print("USB hub SDK not installed")

except DeviceNotFoundError:
    print("USB hub not found - check connection")

except PortStateError as e:
    print(f"Port error: {e}")

except USBBackendError as e:
    print(f"USB error: {e}")

​
Automated Test Setup

from lager import Net, NetType
import time

def setup_test():
    """Power on all USB peripherals for testing."""
    usb_devices = ['PROGRAMMER', 'SENSOR', 'DEBUGGER']

    for name in usb_devices:
        try:
            usb = Net.get(name, type=NetType.Usb)
            usb.enable()
            print(f"{name} powered on")
        except Exception as e:
            print(f"Warning: {name} - {e}")

    time.sleep(1)  # Wait for USB enumeration

    # Enable main power
    psu = Net.get('VDD', type=NetType.PowerSupply)
    psu.set_voltage(3.3)
    psu.enable()

    return True

def teardown_test():
    """Power off all USB peripherals."""
    # Disable main power first
    psu = Net.get('VDD', type=NetType.PowerSupply)
    psu.disable()

    # Power off USB peripherals
    for name in ['PROGRAMMER', 'SENSOR', 'DEBUGGER']:
        try:
            usb = Net.get(name, type=NetType.Usb)
            usb.disable()
        except Exception:
            pass

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USB Device Reset

from lager import Net, NetType
import time

def reset_usb_device(net_name, reset_time=2, settle_time=3):
    """
    Reset a USB device by power cycling.

    Args:
        net_name: USB net name
        reset_time: Time to keep power off (seconds)
        settle_time: Time to wait after power on (seconds)
    """
    usb = Net.get(net_name, type=NetType.Usb)
    print(f"Resetting {net_name}...")

    # Power off
    usb.disable()
    print(f"  Power off for {reset_time}s")
    time.sleep(reset_time)

    # Power on
    usb.enable()
    print(f"  Power on, waiting {settle_time}s for enumeration")
    time.sleep(settle_time)

    print(f"  {net_name} reset complete")

# Usage
reset_usb_device('DUT_USB', reset_time=2, settle_time=5)

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Toggle for Quick State Change

from lager import Net, NetType
import time

# Get USB net
usb = Net.get('LED_USB', type=NetType.Usb)

# Quick on/off cycle using toggle
for i in range(5):
    usb.toggle()
    time.sleep(0.5)

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Supported Hardware

HardwareFeatures
Acroname BrainStem USB HubIndividual port power control, current monitoring
YKUSH USB HubPer-port power switching

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Notes

  • USB nets must be configured on the Lager Box with hub serial number and port mapping
  • Power state changes take effect immediately
  • Allow time for USB enumeration after powering on (~1-3 seconds)
  • Power cycling can be useful for device reset/recovery
  • The toggle() function is useful for quick state changes
  • Use exception handling for robust error recovery