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A simple question about the syntax of OperationRegion


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When I read ACPI Spec, I find this example

OperationRegion (GIO, SystemIO, 0x125, 0x1)
Field (GIO, ByteAcc, NoLock, Preserve) {
IDEI, 1, // IDEISO_EN - isolation buffer
IDEP, 1, // IDE_PWR_EN - power
IDER, 1 // IDERST#_EN - reset#

and also the following description


OperationRegion (RegionName, RegionSpace, Offset, Length)


Declares an operation region named RegionName. Offset is the offset within the selected RegionSpace at

which the region starts (byte-granular), and Length is the length of the region in bytes.

What's the exactly meaning of Length?

There are three arguments, but why the length in the example is one byte ? Is it just because one argument takes one bit, so three arguments take three bits, the unwanted bits (5 bits) are set to zero?


Sorry for my silly question,and really appreciate your answer.


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