Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
Field
ExitBootServices
Exit
Byte
Length
Byte
Offset
Description
8 40 Timer value logged at the point just prior to the OS loader gaining
control back from the ExitBootServices function for UEFI
compatible firmware.
For non-UEFI compatible boots, this field must be zero.
5.2.24 Generic Timer Description Table (GTDT)
This section describes the format of the Generic Timer Description Table (GTDT), which provides
OSPM with information about a system’s Generic Timers configuration. The Generic Timer (GT) is
a standard timer interface implemented on ARM processor-based systems. The GT hardware
specification can be found at Links to ACPI-Related Documents (http://uefi.org/acpi) under the
heading ARM Architecture. The GTDT provides OSPM with information about a system's GT
interrupt configurations, for both per-processor timers, and platform (memory-mapped) timers.
The GT specification defines the following per-processor timers:
• Secure privilege level 1 (EL1) timer,
• Non-Secure EL1 timer,
• Non-Secure privilege level 2 (EL2) timer,
• Virtual timer,
and the following Platform (memory-mapped) timers.
• GT Block
• Server Base System Architecture (SBSA) Generic Watchdog
Table 5-117 GTDT Table Structure
Field
Byte
Length
Byte
Offset
Description
Header
Signature 4 0 ‘GTDT’. Signature for the Generic Timer Description Table.
Length 4 4 Length, in bytes, of the entire Generic Timer Description Table.
Revision 1 8 2
Checksum 1 9 Entire table must sum to zero.
OEMID 6 10 OEM ID.
OEM Table ID 8 16 For the Generic Timer Description Table, the table ID is the
manufacturer model ID.
OEM Revision 4 24 OEM revision of Generic Timer Description Table for supplied
OEM Table ID.
Creator ID 4 28 Vendor ID of utility that created the table.
Creator Revision 4 32 Revision of utility that created the table.
CntControlBase
Physical Address
8 36 The 64-bit physical address at which the Counter Control block
is located.This value is optional if the system implements EL3
(Security Extensions). If not provided, this field must be
0xFFFFFFFFFFFFFFFF
196 April, 2015 Version 6.0