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BT817/8 Advanced Embedded Video Engine Datasheet

Version 1.1

Document No.: BRT_000302 Clearance No.: BRT#154

4.2.4

Clock Frequency

By default the system clock is running at 60MHz when the input clock is 12MHz. The host is allowed to

switch the system clock to other frequencies by the host command “CLKSEL”. The clock switching

command shall be sent in SLEEP mode only.

After the chip is put into Active mode, software shall update the REG_FREQUENCY value to align with the

chosen system clock frequency by CLKSEL command, if the default 60MHz is changed.

4.3 Graphics Engine

4.3.1

Introduction

The graphics engine executes the display list once for every horizontal line. It executes the primitive

objects in the display list and constructs the display line buffer. The horizontal pixel content in the line

buffer is updated if the object is visible at the horizontal line.

Main features of the graphics engine are:



The primitive objects supported by the graphics processor are: lines, points, rectangles,

bitmaps (comprehensive set of formats), text display, plotting bar graph, edge strips, and line

strips, etc.



Operations such as stencil test, alpha blending and masking are useful for creating a rich set

of effects such as shadows, transitions, reveals, fades and wipes.



Anti-aliasing of the primitive objects (except bitmaps) gives a smoothing effect to the viewer.



Bitmap transformations enable operations such as translate, scale and rotate.



Display pixels are plotted with 1/16th pixel precision.



Four levels of graphics states



Tag buffer detection

The graphics engine also supports customized built-in widgets and functionalities such as ASTC

decode, jpeg decode, screen saver, calibration etc. The graphics engine interprets commands from the

MPU host via a 4 Kbyte FIFO in the BT817/8 memory at RAM_CMD. The MPU/MCU writes commands

into the FIFO, and the graphics engine reads and executes the commands. The MPU/MCU updates the

engine updates REG_CMD_READ after commands have been executed.

Main features supported are:



Drawing of widgets such as buttons, clock, keys, gauges, text displays, progress bars, sliders,

toggle switches, dials, gradients, etc.



JPEG and motion-JPEG decode



Inflate functionality (zlib inflate is supported)



Timed interrupt (generate an interrupt to the host processor after a specified number of

milliseconds)



In-built animated functionalities such as displaying logo, calibration, spinner, screen saver and

sketch



Snapshot feature to capture the current graphics display

For

complete

list

graphics

engine

display

commands

and

widgets

refer

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 (unit of

a texture map) resides in. Each block has a fixed memory footprint of 128 bits, but these bits can

represent varying numbers of texels (the block footprint).

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