AML
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| ACPI |
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| Fixed Tables |
| Differentiated Tables |
| Tools/Libs |
ACPI Machine Language (AML) is the platform independent code that ACPI utilizes. A knowledge of it is required to even shutdown the computer. It is found in the DSDT and SSDT tables, which are in turn found by parsing the RSDT or XSDT.
AML code is byte code which is parsed from the beginning of each table when that table is read. It contains definitions of devices and objects within the ACPI namespace. By parsing the code, paying attention to all appropriate control-flow statements, an AML interpreter can build up a database of all devices within a system and the properties and functions they support (in reference to configuration and power management).
The specification is available from the UEFI website. In addition, Intel provides a reference implementation in its ACPICA software.
ASL and AML
ASL is ACPI source language. It is a more human-readable form of the byte code that is AML. This difference is similar to that between assembly code and the actual binary machine code. The Intel ASL assembler (iasl) is freely available on many Linux distributions and can convert in either direction between these formats.
Sample ASL code
The following is a very simple example of ASL code for a DSDT.
test.asl:
DefinitionBlock ("test.aml", "DSDT", 1, "OEMID ", "TABLEID ", 0x00000000)
{
Scope (_SB)
{
Device (PCI0)
{
Name (_HID, EisaId ("PNP0A03"))
}
}
}
This can then be compiled to AML by running 'iasl test.asl' to generate test.aml.
Here is an actual device off an HP pavilion g6 (RTC). This is embedded in a much larger DefinitionBlock:
Device (RTC)
{
Name (_HID, EisaId ("PNP0B00")) // _HID: Hardware ID
Name (_CRS, ResourceTemplate () // _CRS: Current Resource Settings
{
IO (Decode16,
0x0070, // Range Minimum
0x0070, // Range Maximum
0x01, // Alignment
0x08, // Length
)
IRQNoFlags ()
{8}
})
OperationRegion (CMS0, SystemCMOS, Zero, 0x40)
Field (CMS0, ByteAcc, NoLock, Preserve)
{
RTSE, 8,
Offset (0x02),
RTMN, 8,
Offset (0x04),
RTHR, 8,
Offset (0x06),
RTDY, 8,
RTDE, 8
}
}
Notice that the region is in the CMOS.
Following on from the RTC, here is a PS/2 Keyboard off the same PC:
Device (PS2K)
{
Name (_HID, EisaId ("PNP0303")) // _HID: Hardware ID
Method (_STA, 0, NotSerialized) // _STA: Status
{
Return (0x0F)
}
Name (_CRS, ResourceTemplate () // _CRS: Current Resource Settings
{
IO (Decode16,
0x0060, // Range Minimum
0x0060, // Range Maximum
0x01, // Alignment
0x01, // Length
)
IO (Decode16,
0x0064, // Range Minimum
0x0064, // Range Maximum
0x01, // Alignment
0x01, // Length
)
IRQ (Edge, ActiveHigh, Exclusive, )
{1}
})
Name (_PRS, ResourceTemplate () // _PRS: Possible Resource Settings
{
StartDependentFn (0x00, 0x00)
{
FixedIO (
0x0060, // Address
0x01, // Length
)
FixedIO (
0x0064, // Address
0x01, // Length
)
IRQNoFlags ()
{1}
}
EndDependentFn ()
})
Name (_PRW, Package (0x02) // _PRW: Power Resources for Wake
{
0x18,
0x03
})
Method (_PSW, 1, NotSerialized) // _PSW: Power State Wake
{
Store (Arg0, KBWK)
}
}
the above 2 samples were gathered via a utility I wrote to snatch DSDT data from the Registry, disassembled by iASL.--Bellezzasolo 14:58, 20 January 2013 (CST)
This defines one table (the DSDT), and requests that the output AML be placed in a file called test.aml. The "OEMID " is a 6 character string defining the name of the OEM who made the firmware of the system, the "TABLEID " is an 8 character string defining the name of the table - it is normally OEM specific. The last entry in the DefinitionBlock line is the OEM revision id. It defines one namespace within the root namespace which is called _SB. Note that all device/scope/object names are 4 characters long, therefore this is sometimes represented as "_SB ". _SB is a special name in the ACPI namespace called "System Bus", which is the main scope under which all devices and bus objects are found. See the ACPI specification table 5-67 for a list of predefined names.
Within the _SB scope we define a device called PCI0, which has one object within it called _HID. _HID is again a predefined name that refers to a device's Plug and Play hardware ID, in this case the built-in macro EisaId is used to generate the value 0x030ad041 from "PNP0A03", which is the PNP ID of a PCI root bus. A reasonably complete list of PNP ids is available from http://tuxmobil.org/pnp_ids.html.
AML Opcodes
This table comes from the ACPI specification, where it is provided mainly for use during debugging an AML parser. For example, if your parser fails and the next byte (that it couldn't parse) is "0x72" then you could refer to this table to see that it is an "Add" operation. Don't let this table confuse you into thinking that AML consists a linear flow of simple instructions to be decoded one at a time. Most AML consists of nested, recursively defined structures and lists.
| Value (Hex) | Name |
|---|---|
| 0x00 | ZeroOp |
| 0x01 | OneOp |
| 0x06 | AliasOp |
| 0x08 | NameOp |
| 0x0A | BytePrefix |
| 0x0B | WordPrefix |
| 0x0C | DWordPrefix |
| 0x0D | StringPrefix |
| 0x0E | QWordPrefix |
| 0x10 | ScopeOp |
| 0x11 | BufferOp |
| 0x12 | PackageOp |
| 0x13 | VarPackageOp |
| 0x14 | MethodOp |
| 0x15 | ExternalOp |
| 0x2E (‘.’) | DualNamePrefix |
| 0x2F (‘/’) | MultiNamePrefix |
| 0x30-0x39 ('0'-'9') | DigitChar |
| 0x41-0x5A (‘A’-‘Z’) | NameChar |
| 0x5B (‘[’) | ExtOpPrefix |
| 0x5B 0x01 | MutexOp |
| 0x5B 0x02 | EventOp |
| 0x5B 0x12 | CondRefOfOp |
| 0x5B 0x13 | CreateFieldOp |
| 0x5B 0x1F | LoadTableOp |
| 0x5B 0x20 | LoadOp |
| 0x5B 0x21 | StallOp |
| 0x5B 0x22 | SleepOp |
| 0x5B 0x23 | AcquireOp |
| 0x5B 0x24 | SignalOp |
| 0x5B 0x25 | WaitOp |
| 0x5B 0x26 | ResetOp |
| 0x5B 0x27 | ReleaseOp |
| 0x5B 0x28 | FromBCDOp |
| 0x5B 0x29 | ToBCD |
| 0x5B 0x2A | UnloadOp |
| 0x5B 0x30 | RevisionOp |
| 0x5B 0x31 | DebugOp |
| 0x5B 0x32 | FatalOp |
| 0x5B 0x33 | TimerOp |
| 0x5B 0x80 | OpRegionOp |
| 0x5B 0x81 | FieldOp |
| 0x5B 0x82 | DeviceOpList |
| 0x5B 0x83 | ProcessorOp |
| 0x5B 0x84 | PowerResOp |
| 0x5B 0x85 | ThermalZoneOpList |
| 0x5B 0x86 | IndexFieldOp |
| 0x5B 0x87 | BankFieldOp |
| 0x5B 0x88 | DataRegionOp |
| 0x5C (‘\’) | RootChar |
| 0x5E (‘^’) | ParentPrefixChar |
| 0x5F(‘_’) | NameChar |
| 0x60 (‘`’) | Local0Op |
| 0x61 (‘a’) | Local1Op |
| 0x62 (‘b’) | Local2Op |
| 0x63 (‘c’) | Local3Op |
| 0x64 (‘d’) | Local4Op |
| 0x65 (‘e’) | Local5Op |
| 0x66 (‘f’) | Local6Op |
| 0x67 (‘g’) | Local7Op |
| 0x68 (‘h’) | Arg0Op |
| 0x69 (‘i’) | Arg1Op |
| 0x6A (‘j’) | Arg2Op |
| 0x6B (‘k’) | Arg3Op |
| 0x6C (‘l’) | Arg4Op |
| 0x6D (‘m’) | Arg5Op |
| 0x6E (‘n’) | Arg6Op |
| 0x70 | StoreOp |
| 0x71 | RefOfOp |
| 0x72 | AddOp |
| 0x73 | ConcatOp |
| 0x74 | SubtractOp |
| 0x75 | IncrementOp |
| 0x76 | DecrementOp |
| 0x77 | MultiplyOp |
| 0x78 | DivideOp |
| 0x79 | ShiftLeftOp |
| 0x7A | ShiftRightOp |
| 0x7B | AndOp |
| 0x7C | NandOp |
| 0x7D | OrOp |
| 0x7E | NorOp |
| 0x7F | XorOp |
| 0x80 | NotOp |
| 0x81 | FindSetLeftBitOp |
| 0x82 | FindSetRightBitOp |
| 0x83 | DerefOfOp |
| 0x84 | ConcatResOp |
| 0x85 | ModOp |
| 0x86 | NotifyOp |
| 0x87 | SizeOfOp |
| 0x88 | IndexOp |
| 0x89 | MatchOp |
| 0x8A | CreateDWordFieldOp |
| 0x8B | CreateWordFieldOp |
| 0x8C | CreateByteFieldOp |
| 0x8D | CreateBitFieldOp |
| 0x8E | TypeOp |
| 0x8F | CreateQWordFieldOp |
| 0x90 | LandOp |
| 0x91 | LorOp |
| 0x92 | LnotOp |
| 0x92 0x93 | LNotEqualOp |
| 0x92 0x94 | LLessEqualOp |
| 0x92 0x95 | LGreaterEqualOp |
| 0x93 | LEqualOp |
| 0x94 | LGreaterOp |
| 0x95 | LLessOp |
| 0x96 | ToBufferOp |
| 0x97 | ToDecimalStringOp |
| 0x98 | ToHexStringOp |
| 0x99 | ToIntegerOp |
| 0x9C | ToStringOp |
| 0x9D | CopyObjectOp |
| 0x9E | MidOp |
| 0x9F | ContinueOp |
| 0xA0 | IfOp |
| 0xA1 | ElseOp |
| 0xA2 | WhileOp |
| 0xA3 | NoopOp |
| 0xA4 | ReturnOp |
| 0xA5 | BreakOp |
| 0xCC | BreakPointOp |
| 0xFF | OnesOp |