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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

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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. 
from lager import Net, NetType

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

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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

​
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)

​
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