USB Control

Control USB device power state

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

Import

from lager import Net, NetType

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

Methods

Method	Description
enable()	Enable (power on) USB port
disable()	Disable (power off) USB port
toggle()	Toggle USB port power state

Exception Classes

Exception	Description
USBBackendError	Base class for USB hub errors
LibraryMissingError	Required vendor SDK not installed
DeviceNotFoundError	USB hub not found
PortStateError	Error changing port state

Method Reference

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:

Parameter	Type	Description
name	str	Name of the USB net
type	NetType	Must be NetType.Usb

Returns: USB Net instance

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")

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")

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

Examples

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")

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')

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)

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

Hardware	Features
Acroname BrainStem USB Hub	Individual port power control, current monitoring
YKUSH USB Hub	Per-port power switching

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