GXLV Datasheet, PDF (141/247 Pages) National Semiconductor (TI) – Geode™ GXLV Processor Series Low Power Integrated x86 Solutions

Integrated Functions (Continued)
4.5.7.3 VGA Display Support
The graphics pipeline contains full hardware support for
the VGA front end. The VGA data is stored in a 256 KB
buffer located in graphics memory. The main task for Vir-
tual VGA (see Section 4.6 “Virtual VGA Subsystem” on
page 157) is converting the data in the VGA buffer to an 8-
bpp frame buffer that can be displayed by the display con-
troller.
For some modes, the display controller can display the
VGA data directly and the data conversion is not neces-
sary. This includes standard VGA mode 13h and the vari-
ations of that mode used in several games; the display
controller can also directly display VGA planar graphics
modes D, E, F, 10, 11, and 12. Likewise, the hardware can
directly display all of the higher-resolution VESA modes.
Since the frame buffer data is written directly to memory
instead of travelling across an external bus, the GXLV pro-
cessor often outperforms VGA cards for these modes.
The display controller, however, does not directly support
text modes. SoftVGA must convert the characters and
attributes in the VGA buffer to an 8-bpp frame buffer
image the hardware uses for display refresh.
4.5.8 Display Controller Registers
The Display Controller maps 100h memory locations
starting at GX_BASE+8300h for the display controller reg-
isters. Refer to Section 4.1.2 “Control Registers” on page
99 for instructions on accessing these registers.
The Display Controller Registers are divided into six cate-
gories:
• Configuration and Status Registers
• Memory Organization Registers
• Timing Registers
• Cursor and Line Compare Registers
• Color Registers
• Palette and RAM Diagnostic Registers
Table 4-28 summarizes these registers and locations, and
the following subsections give detailed register/bit for-
mats.
Table 4-28. Display Controller Register Summary
GX_BASE+
Memory Offset Type Name/Function
Configuration and Status Registers
8300h-8303h
8304h-8307h
8308h-830Bh
830Ch-830Fh
R/W
R/W
R/W
R/W
DC_UNLOCK
Display Controller Unlock: This register is provided to lock the most critical memory-
mapped display controller registers to prevent unwanted modification (write operations).
Read operations are always allowed.
DC_GENERAL_CFG
Display Controller General Configuration: General control bits for the display controller.
DC_TIMING_CFG
Display Controller Timing Configuration: Status and control bits for various display
timing functions.
DC_OUTPUT_CFG
Display Controller Output Configuration: Status and control bits for pixel output
formatting functions.
Memory Organization Registers
8310h-8313h
8314h-8317h
8318h-831Bh
831Ch-831Fh
8320h-8323h
8324h-8327h
R/W
R/W
R/W
--
R/W
R/W
DC_FB_ST_OFFSET
Display Controller Frame Buffer Start Address: Specifies offset at which the frame buffer
starts.
DC_CB_ST_OFFSET
Display Controller Compression Buffer Start Address: Specifies offset at which the com-
pressed display buffer starts.
DC_CUR_ST_OFFSET
Display Controller Cursor Buffer Start Address: Specifies offset at which the cursor mem-
ory buffer starts.
Reserved
DC_VID_ST_OFFSET
Display Controller Video Start Address: Specifies offset at which the video buffer starts.
DC_LINE_DELTA
Display Controller Line Delta: Stores line delta for the graphics display buffers.
Default
Value
00000000h
00000000h
xx000000h
xx000000h
xxxxxxxxh
xxxxxxxxh
xxxxxxxxh
00000000h
xxxxxxxxh
xxxxxxxxh
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