Architecture Overview (Continued)
1.5.2 Display Controller
The memory controller handles multiple requests for
memory data from the GXm processor, the graphics
accelerator and the display controller. The memory con-
troller contains extensive buffering logic that helps mini-
mize contention for memory bandwidth between graphics
and CPU requests. The memory controller cooperates
with the internal bus controller to determine the cacheabil-
ity of all memory references.
The display port is a direct interface to the CS5530 which
drives a TFT flat panel display, LCD panel, or a CRT dis-
play.
The display controller (video generator) retrieves image
data from the frame buffer region of memory, performs a
color-look-up if required, inserts the cursor overlay into
the pixel stream, generates display timing, and formats
the pixel data for output to a variety of display devices.
The display controller contains Display Compression
Technology (DCT) that allows the GXm processor to
refresh the display from a compressed copy of the frame
buffer. DCT typically decreases the screen-refresh band-
width requirement by a factor of 15 to 20, further minimiz-
ing bandwidth contention.
1.5.4 PCI Controller
The GXm processor incorporates a full-function PCI inter-
face module that includes the PCI arbiter. All accesses to
external I/O devices are sent over the PCI bus, although
most memory accesses are serviced by the SDRAM con-
troller. The Internal Bus Interface Unit contains address
mapping logic that determines if memory accesses are
targeted for the SDRAM or for the PCI bus.
1.5.3 XpressRAM Memory Subsystem
The memory controller drives a 64-bit SDRAM port
directly. The SDRAM memory array contains both the
main system memory and the graphics frame buffer. Up to
four module banks of SDRAM are supported. Each mod-
ule bank will have two or four component banks depend-
ing on the memory size and organization. The maximum
configuration is four module banks with four component
banks providing a total of 16 open banks. The maximum
memory size is 1 GB.
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