Intel Extensible Firmware Interface - Manual (Page 734)

Extensible Firmware Interface Specification
16-20 12/01/02 Version 1.10
16.3.2 Debugport Device Path
The debugport driver must establish and maintain an instance of the EFI Device Path protocol for
the debugport. A graceful handoff of debugport ownership between the EFI Debugport driver and
an OS debugport driver requires that the OS debugport driver can determine the type, location, and
configuration of the debugport device.
The Debugport Device Path is a vendor-defined messaging device path with no data, only a GUID.
It is used at the end of a conventional device path to tag the device for use as the debugport. For
example, a typical UART debugport would have the following fully qualified device path:
ACPI(PciRootBridge)/Pci(0x1f,0)/ACPI(PNP0501,0)/UART(115200,n,8,1)/DebugPort()
The Vendor_GUID that defines the debugport device path is the same as the debugport protocol
GUID, as defined below.
#define DEVICE_PATH_MESSAGING_DEBUGPORT \
EFI_DEBUGPORT_PROTOCOL_GUID
Table 16-1 shows all fields of the debugport device path.
Table 16-1. Debugport Messaging Device Path
Mnemonic Byte
Offset Byte
Length
Description
Type 0 1 Type 3 – Messaging Device Path.
Sub Type 1 1 Sub Type 10 – Vendor.
Length 2 2 Length of this structure in bytes. Length is 20 bytes.
Vendor_GUID 4 16 DEVICE_PATH_MESSAGING_DEBUGPORT .