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TVP4020
Programmers Reference Manual
Programming Model
13
do any pre-work
get free DMA buffer and mark as in use
put render data into this new buffer
DMAAddress(address of new buffer)
while (TRUE) {
count = *DMACount;
// note this is volatile
if (count) {
while (--count)
;
// wait for count to expire
}
else
break;
// DMA completed
}
DMACount(number of words in new buffer)
mark the old buffer as free
return
In general the DMA buffer format consists of a 32-bit address tag
description word followed by one or more data words. The DMA buffer
consists of one or more sets of these formats. The following paragraphs
describe the different types of tag description words that can be used.
DMA Tag Description Format
When DMA is performed each 32-bit tag description in the DMA buffer
conforms to the following format.
reserved
0
8
16
24
31
Count or Mask
Address Tag
reserved
Mode
0 = Hold tag
1 = Increment tag
2 = Indexed
tag
3 = Reserved
Figure 3.1
DMA Tag Description Format
There are 3 different tag addressing modes for DMA: hold, increment
and indexed. The different DMA modes are provided to reduce the
amount of data which needs to be transferred, hence making better use
of the available DMA bandwidth. Each of these is described in the
following sections. Each row in the following diagrams represents a 32-
bit value in the DMA buffer. The address tag for each register is given in
the Graphics Register Reference Appendix D.
Hold Format
Summary of Contents for TVP4020 PERMEDIA 2
Page 1: ...Texas Instruments TVP4020 PERMEDIA 2 Programmer s Reference Manual Issue 4 ...
Page 284: ...TVP4020 Programmers Reference Manual A Gouraud Shaded Triangle 275 ...
Page 292: ...TVP4020 Programmers Reference Manual Register Tables 283 ...
Page 314: ...TVP4020 Programmers Reference Manual Index 305 ...
Page 315: ...Index TVP4020 Programmers Reference Manual 306 Index ...
Page 323: ...Index TVP4020 Programmers Reference Manual 314 ...