Advanced Configuration and Power Interface Specification

ACPI Software Programming Model
// Create the GenericSerialBus data buffer
Name(BUFF, Buffer(34){})
// Create SerialBus buf as BUFF
CreateByteField(BUFF, 0x00, STAT) // STAT = Status (Byte)
CreateBytefield(BUFF, 0x01, LEN) // LEN = Length (Byte)
CreateWordField(BUFF, 0x03, DATW) // DATW = Data (Word - Bytes 2 & 3, or 16 bits)
CreateField(BUFF, 16, 256, DBUF) // DBUF = Data (Bytes 2-33)
CreateField(BUFF, 16, 32, DATD) // DATD = Data (DWord)
// Read block of data from the device using command value 0
Store(TFK1, BUFF)
If(LNotEqual(STAT, 0x00)) {
Return(0)
}
// Read block of data from the device using command value 1
Store(TFK2, BUFF)
If(LNotEqual(STAT, 0x00)) {
Return(0)
}
In this example, two field elements (TFK1, and TFK2) are defined to represent the virtual registers
for command values 0 and 1. Access to any of the field elements will cause a GenericSerialBus
transaction to occur to the device.
Writing blocks of data requires similar semantics, such as in the following example.
Store(16, LEN) // In bits, so 4 bytes
Store(Store(BUFF, TFK1), BUFF) // Invoke Write Block transaction
If(LEqual(STAT, 0x00)) {…}
// Transaction successful?
This accessor is not viable for some SPBs because the bus may not support the appropriate
functionality. In cases that variable length buffers are desired but the bus does not support block
accessors, refer to the SerialBytes protocol.
5.5.2.4.5.3.6 Word Process Call (AttribProcessCall)
The GenericSerialBus Process Call protocol (AttribProcessCall) transfers 2 bytes of data bidirectionally
(performs a Write Word followed by a Read Word as an atomic transaction). This
protocol uses a command value to reference up to 256 word-sized virtual registers.
The following ASL code illustrates how a device supporting the Process Call protocol should be
accessed:
OperationRegion(TOP1, GenericSerialBus, 0x00, 0x100) // GenericSerialBus device at slave address
0x42
Field(TOP1, BufferAcc, NoLock, Preserve)
{
}
Connection(I2CSerialBus(0x5a,,100000,,"\_SB.I2C",,,,RawDataBuffer(){1,6}))
AccessAs(BufferAcc, AttribProcessCall) // Use the GenericSerialBus Process Call protocol
FLD0, 8, // Virtual register at command value 0.
FLD1, 8, // Virtual register at command value 1.
FLD2, 8 // Virtual register at command value 2.
// Create the GenericSerialBus data buffer
Name(BUFF, Buffer(6){})
// Create GenericSerialBus data buffer as BUFF
CreateByteField(BUFF, 0x00, STAT) // STAT = Status (Byte)
CreateWordField(BUFF, 0x02, DATA) // DATA = Data (Word)
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