Specifications

AMD Geode™ GeodeROM Functional Specification 237
16
Virtual Hardware 32087C
16.0Virtual Hardware
AMD Geode™ solutions and the GeodeROM SMM software make it possible to emulate hardware functionality. The firm-
ware responds to SMIs generated by specialized hardware and provides virtual devices such as the XpressAUDIO™ sub-
system, the XpressGRAPHICS™ subsystem, RTC/CMOS devices, and UARTs.
16.1 Virtual Video
Note: Section 16.1 applies to SoftVGA and the Geode GX1 processor only. For other SMI handlers, see their graphics
software specification.
Using Virtual System Architecture™ technology, GeodeROM optionally includes support for SoftVGA. SoftVGA takes
advantage of embedded hardware capability to provide a VGA graphics subsystem compatible with the IBM VGA with addi-
tional functionality to support the VESA BIOS extensions.
The SoftVGA virtualizes the video interface by supporting the standard VGA interface with the VESA BIOS extensions and
a single indexed register. This register operates as an indexed pair such that the register index is written to 0AC1Ch, and
the data is then read from or written to 0AC1Eh. This register is used to define three initialization parameters: the size of the
video memory in 128 KB segments, determine whether SoftVGA is to be enabled, and if enabled, determine whether it is to
be initially active. This register is to be written only at initialization. Writing this register after initialization creates unpredict-
able results. After initialization, the preferred video interface is the standard VGA interface.
The initialization parameters fit within one byte and have the format of that shown in Table 16-1.
Example 1:
; Set the SoftVGA initialization parameters
mov dx, 0AC1Ch ; The index register address
mov ax, 0200h ; The index of the initialization register
out dx, ax ; Set the index
mov dx, 0AC1Eh ; The data register address
mov ax, 0029h ; SoftVGA installed and initially active, 2.5 MB video memory
Table 16-1. Virtual Video Register
Register
Index
Register Name
or Use Access Description
0200h Video initialization Write Only Set the video initialization parameters. Default is SoftVGA installed and
on, using the memory size specified during the GeodeROM configura-
tion. The bit formats are:
Bit 7:
0 = SoftVGA is initially active
1 = SoftVGA is initially inactive (used for dual-monitor support).
Bits [6:1]:
Amount of video memory in 128 KB blocks.
Bit 0:
0 = SoftVGA is not to be installed
1 = Install SoftVGA.