Owner's manual

Table Of Contents
DS785UM1 8-13
Copyright 2007 Cirrus Logic
Graphics Accelerator
EP93xx User’s Guide
8
8
Note:The word count for this example would be: 6 - 1 = 5 words, since P6 ends in the 6th word.
The word count takes into account the whole pixel, not just the starting location. So,
WIDTH = 0x5 would be written to the “BLKDESTWIDTH” register.
8.6 Register Usage
Since some registers have different meanings based on the type of transfer being performed,
the next section will give the use and meaning of the register during the various graphics
transfers.
8.6.1 Breshenham’s Algorithm Line Draw
The following sequence describes how to set up the registers that are used for a
Breshenham algorithm line draw:
1. Setup LINEINIT Register
Write YINIT = 0x800 (2048) and XINIT = 0x800 in the “LINEINIT” register.
2. Setup LINEPATTERN Register
A. Write desired values to the Pattern (PTRN) and Count (CNT) fields to create solid or
patterned lines. The “LINEPATTRN” register contains a 4-bit pattern Count (CNT)
value and a 16-bit Pattern (PTRN) that defines 16 pixel on/off patterns for line
functions. CNT specifies the position of the last bit used in the PTRN field starting at
bit 0 of the PTRN field.
B. For a solid line, write CNT = 0xF and PTRN = 0xFFFF to the “LINEPATTRN
register. The solid line will have the color value that is written to the MASK field in
the “BLOCKMASK” register.
C. For a pattern of 8 ‘on’ pixels and 8 ‘off’ pixels, write CNT = 0xF and PTRN = 0x00FF
to the “LINEPATTRN” register. The 8 ‘on’ pixels would have the color value that is
written to the MASK field in the “BLOCKMASK” register. The 8 ‘off’ pixels would
either be transparent as specified by BG = ‘0’ in the “BLOCKCTRL” register or have
the color value written to the “BACKGROUND” register as specified by BG = ‘1’ in
the “BLOCKCTRL” register. Using DX/DY line draw, the pattern will be more
consistent for any line regardless of angle.
Table 8-20. 24 BPP Memory Layout for Destination Image
Address 31 24 23 16 15 8 7 0
0x0058
P1 P0 P0 P0
0x005C
P2 P2 P1 P1
0x0060
P3 P3 P3 P2
0x0064
P5 P4 P4 P4
0x0068
P6 P6 P5 P5
0x006C P7 P7 P7
P6