FADT: Difference between revisions
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{{ACPI}}
'''FADT''' (Fixed ACPI Description Table) is a data structure used in the [[ACPI]] programming interface. This table contains information about fixed register blocks pertaining to power management.▼
''This page is about the ACPI FADT(Fixed ACPI Description Table)''
It contains information about ACPI fixed registers, DSDT pointer, etc.
▲'''FADT'''
==Finding the FADT==
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==Structure==
The FADT is a complex structure and contains a lot of data. Here it is:
<
{
struct ACPISDTHeader h;
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GenericAddressStructure X_GPE0Block;
GenericAddressStructure X_GPE1Block;
};</
== GenericAddressStructure ==
Before going to far, keep in mind that the GAS is a structure used by ACPI to describe the position of registers. Its structure is:
<
{
uint8_t AddressSpace;
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uint8_t AccessSize;
uint64_t Address;
};</
{| border="1"
|+ Possible values of AddressSpace
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| 1 || System I/O
|-
| 2 || [[PCI]] Configuration Space
|-
| 3 || Embedded Controller
|-
| 4 || [[SMBus|System Management Bus]]
|-
| 5
|-
| 6 || PCI Device [https://wiki.osdev.org/PCI#PCI_Device_Structure BAR] Target
|-
| 7 || [[IPMI|Intelligent Platform Management Infrastructure]]
| 0x80 to 0xBF || Reserved▼
|-
| 8 || [[General Purpose I/O]]
| 0xC0 to 0xFF || OEM Defined▼
|-
| 9 || [[Generic Serial Bus]]
|-
| 0x0A || [[PCC|Platform Communication Channel]]
|-
|-
|}
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| 1 || Byte access
|-
| 2 || 16-bit
|-
| 3 || 32-bit
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| 4 || 64-bit
|}
Address is a
== Fields ==
=== FirmwareCtrl ===
This is a 32-bit pointer to the [[FACS]]. Since ACPI 2.0 a new field has been added to the table, X_FirmwareControl of type [[#GenericAddressStructure|GAS]], which is 64-
=== Dsdt ===
A 32-bit pointer to the [[DSDT]]. This has a X_Dsdt brother too.
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|}
=== SCI_Interrupt ===
The System Control Interrupt is used by ACPI to notify the OS about fixed events, such as for example, pressing the power button, or for General Purpose Events (GPEs), which are firmware specific. This member in the FADT structure indicates the [[PIC]] or [[IOAPIC]] interrupt pin for it. To know if it's a PIC IRQ, check if the dual 8259 interrupt controllers are present via the [[MADT]]. Otherwise, it's a GSI. If you are using the IOAPIC and the PIC is present, remember to check the Interrupt Source Overrides first to get the GSI associated with the IRQ source.
=== SMI_CommandPort ===
This is an I/O Port. This is where the OS writes AcpiEnable or AcpiDisable to get or release the ownership over the ACPI registers. This is 0 on systems where the [[System Management Mode]] is not supported.
== What's next? ==
You should preserve the pointer to the [[FACS]] (in FirmwareControl (if <
[[Category:ACPI]]
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