Accelerated Graphics Port Interface Specification

AGP3.0 Interface Specification
Rev. 1.0
141
Bits Access Field Description
“1s” for the APSIZE encoding for its maximum
aperture size. For e.g. if core logic supports 256MB
max, it must hardwire APSIZE[11:8] to ‘1’. Writes to
these bits will have no effect.
• Min Aperture Size: If this is different from the table
above, the core logic must hardwire the “0s” in the
encoding for its min aperture size. For e.g. if min
supported size is 16MB, APSIZE[1,0] must be
hardwired to ‘0. Write will have no effect.
The above scheme forces the aperture to be always naturally
aligned to the selected aperture size.
5.9.5 NEPG: AGP ENABLED APERTURE PAGE SIZE
Offset: CAPPTR + 16h
Size: 2 bytes
Table 72: Enabled Page
Bits Access Field Description
15:12 R-W-
D’0000
20
SEL Size Select (SEL) selects the AGP aperture Page Size from field N.
For example, if SEL = 0111b, this will select NEPG[7] or an aperture
Page Size of 512KB if the bit is set. Default for SEL = 0 is N = 0 or
4KB Page Size support.
If the following requirements are not met for the value of NEPG.SEL it
is unpredictable which AGP aperture Page size, if any, is selected:
• SEL ranges from b’0000 to b’1010 (all other values undefined)
• NEPG[SEL}] must be ‘1’.
11 RZ-MW Reserved Reserved
10:0 R-IW N NEPG[bit N] indicates whether the Core-logic implementation supports
an AGP3.0 aperture Page size of (2 ^ (N+12)).
If NEPG[bit N] is ‘1’, then the corresponding AGP aperture page size is
supported; if ‘0’ then the size is not supported.
For example, if NEPG bit 7 is set, then the implementation supports an
AGP aperture page size of (2 ^ (7+12)) or 512KB.
NEPG[6] must be ‘1’ by all implementations to support 4 KB page size.
The largest page size supportable is 4MB.
4KB page must always be supported. This means NEPG[0] must = 1
for all core-logic implementations.
20
If an implementation supports only 1 page size (4KB) , then this field may be implemented as Read-Only.