Data Sheet

Copyright © Bridgetek Pte Ltd 22
BT81X (815/6) Advanced Embedded Video Engine Datasheet
Version 1.0
Document No.: BRT_000220 Clearance No.: BRT#126
 In-built animated functionalities such as displaying logo, calibration, spinner, screen saver and
sketch
 Snapshot feature to capture the current graphics display
For a complete list of graphics engine display commands and widgets refer to
BT81X_Series_Programming_Guide, Chapter 4.
4.3.2 ASTC
ASTC stands for Adaptive Scalable Texture Compression, an open standard developed by ARM for use in
mobile GPUs.
ASTC is a block-based lossy compression format. The compressed image is divided into a number of
blocks of uniform size, which makes it possible to quickly determine which block a given texel resides in.
Each block has a fixed memory footprint of 128 bits, but these bits can represent varying numbers of
texels (the block footprint).
Block footprint sizes are not confined to powers-of-two, and are also not confined to be square. For 2D
formats the block dimensions range from 4 to 12 texels.
Using ASTC for the large ROM fonts can save considerable space. Encoding the four largest fonts in ASTC
8x8 formats gives no noticeable loss in quality and reduces the ROM size from 1 MByte to about 640
Kbytes.
4.3.3 ROM and RAM Fonts
The BT815/6 has built in ROM character bitmaps as font metrics. The graphics engine can use these
metrics when drawing text fonts. There are a total of 19 ROM fonts, numbered with font handle 16-34.
Fonts 31-34 are large ROM fonts encoded in ASTC 8x8 format. The user can define and load customized
font metrics into RAM_G or external flash, making it possible to support a full range of Unicode characters
with UTF-8 coding points.
Each ROM font metric block has a 148 byte font table which defines the parameters of the font and the
pointer of font image. The font table format is shown in Table 4-7.
Address Offset
Size(byte)
Parameter Description
0
128
width of each font character, in pixels
128
4
font bitmap format, for example L1, L4 or L8
132
4
font line stride, in bytes
136
4
font width, in pixels
140
4
font height, in pixels
144
4
pointer to font image data in memory
Table 4-7 Font Table Format
The ROM fonts are stored in the memory space ROM_FONT. The ROM font table is also stored in the
ROM. The starting address of the ROM font table for font index 16 is stored at ROM_FONT_ADDR, with
other font tables following. The ROM font table and individual character width (in pixel) are listed in Table
4-8, Table 4-9 and Table 4-10. Font index 16, 18 and 20-31 are for basic ASCII characters (code 0-127),
while font index 17 and 19 are for Extended ASCII characters (code 128-255). The character width for
font index 16 through 19 is fixed at 8 pixels for any of the ASCII characters.
Font Index
1
6
1
7
1
8
1
9
2
0
2
1
2
2
2
3
2
4
2
5
2
6
2
7
2
8
2
9
3
0
3
1
3
2
3
3
3
4
Font format
L
1
L
1
L
1
L
1
L
1
L
1
L
1
L
1
L
1
L
1
L
4
L
4
L
4
L
4
L
4
L
4
L
4
L
4
L
4
Line stride
1
1
1
1
2
2
2
3
3
4
7
8
9
1
1
1
4
1
8
2
3
3
0
3
9
Font width
(max)
8
8
8
8
1
1
1
3
1
7
1
8
2
5
3
4
1
3
1
5
1
9
2
1
2
8
3
7
4
9
6
3
8
2
Font height
8
8
1
1
1
1
2
2
2
3
1
2
2
2
3
4
6
8
1