Samsung S5PC100, User Manual

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3D-ACCELERATOR S5PC100 USER’S MANUAL (REV1.0)
9.6-24
3.2.1 Index Mode
Index mode uses the Vertex Buffer in Host Interface. There are two operation modes: auto-increment mode and
index-transfer mode. NOTE: All of the geometry data must be in the Vertex Buffer. Also, the range of used indices
is deeply related to the VB size: the VB address calculated with indices must be the available VB address. Hence
the indices must be carefully controlled by the application program (or the device driver).
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Auto-increment mode (HI_CONTROL.EnVB=1, HI_CONTROL.AutoInc=1) : CPU sends two DWORDs
representing a count (the number of vertices) and an index (the first index into the Vertex Buffer), to the Host
Interface. Host Interface uses the transferred index for the index to the Vertex Buffer. And then, the next
index is automatically calculated; HI_IDXOFFSET.VALUE is added to the previous index (usually set to 1).
This process is repeated count-times. Each pair of DWORDs (count and index value) represents a set of
indices. Therefore, this scheme maximizes the performance in transferring geometry data.
Figure 9.6- 6 Auto-Increment Mode
In Figure 9.6- 7, six sets of the geometries are transferred from CPU.
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Index-transfer mode (HI_CONTROL.EnVB=1, HI_CONTROL.AutoInc=0) : In index-transfer mode, CPU
sends the individual indices. After CPU sending the number of indices (count), a set of random indices are
transferred. These indices are used to index the Vertex Buffer.
{TO BE DONE: HI_IDXOFFSET can be used
to bias the sent index; (sent index + HI_IDXOFFSET) is used as a new index}.
Figure 9.6- 8 Index-Transfer Mode