There's more information in the actual specification of the I/O port descriptor:
Base alignment, _ALN: Alignment for minimum base address, increment in 1-byte blocks.
I believe this is the required alignment within I/O space for the base address that is
programmed into the device. Where 0,1 = Byte aligned, 2 = word aligned, 4 = dword aligned,
From: devel-bounces(a)acpica.org [mailto:[email protected]
] On Behalf
Of master chief
Sent: Thursday, December 03, 2009 11:28 AM
Subject: [Devel] Base Address Granularity
In the ACPI specification, under IO (IO Resource Descriptor Macro) I read:
"AddressAlignment evaluates to an 8-bit integer that specifies the
alignment granularity for the I/O address assigned. The field
DescriptorName. _ALN is automatically created to refer to this portion of
the resource descriptor."
And while the latter part about the addition of _ALN is perfectly clear to
me, I have trouble understanding the former part. I looked at a number of
Apple, Asus and GigaByte DSDT's and there I find Apple and GigaByte using a
granularity of 0x01 and Asus 0x00.
Apparently both work, even in my own DSDT code, but I cannot for the life
of me find anything related to the exact meaning of this "granularity".
Please advise. Thank you.
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