_UID Deep Dive

Firmware-debug focused ACPI identity note.

June 10, 2026 1 min read

_UID distinguishes multiple ACPI devices that share the same hardware ID.

This becomes important when a platform has several similar devices: multiple I2C controllers, multiple batteries, multiple thermal zones, or repeated GPIO-backed devices.

Device (BAT0)
{
    Name (_HID, EisaId ("PNP0C0A"))
    Name (_UID, Zero)
}

Device (BAT1)
{
    Name (_HID, EisaId ("PNP0C0A"))
    Name (_UID, One)
}

Debug Diary

If two devices have the same _HID and confusing _UID values, OS logs and driver instances can become hard to map back to the schematic. During debug, _UID is often the breadcrumb that connects OS-visible instances to board-level reality.

_UID debug checklist

Check devices with duplicate _HID values.
Map _UID values to board schematics or silk labels.
Avoid changing _UID casually; OS device persistence can depend on it.
Confirm that hotplug or SKU-specific devices still produce stable IDs.

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Debug Diary

_UID debug checklist

Related notes

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