4/29/2020
Godson 3A1000 Processor User Manual
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Godson 3A1000 Processor User Manual Part 2
16 X system memory allocation
The memory allocation problem of the X system describes the video memory allocation problem. In 3A-690e, the graphics card is set
It is inside the North Bridge 690E and is a device of PCIE. The display core of the graphics card is ATI X1250, integrated inside
128M video memory also supports shared video memory. The maximum shared video memory can be up to 128M. The display process of the graphics card is this
Similar: The CPU transfers the instructions and data related to drawing to the graphics card through the PCIE bus. GPU according to CPU requirements
To complete the image processing process and save the final image data in the video memory.
Figure 16-1 Graphics card processing image display process
For the case of using independent video memory, since the video memory is inside the graphics card, the process becomes
The card can directly write the content to the video memory. For shared video memory, the process is a bit more complicated, the GPU will write
After the video memory address is told to the CPU, there will be two situations: 1. The video memory address is a PCI space address. CPU will put
The content is directly written to the PCIE bus, and PCIE performs another address conversion to the actual memory address, which is
Is the physical address; second, the memory address is the memory address. At this time, the CPU will directly write the content to the video memory in the memory
position. Obviously, for the method of shared memory, the second scheme will be more efficient.
The following specifically describes how to implement the second way of sharing video memory in PMON Chinese. To expand our PCI
Space, we use TLB mapping. In bonito.h of PMON, we define it like this:
