Bridgetek FT801 - Screenshot; Performance

FT800 Series Programmer Guide
Version 2.1
Document Reference No.: BRT_000030 Clearance No.: BRT#037
30
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2.5.8 Screenshot
The code below demonstrates how to utilize the registers and RAM_SCREENSHOT to
capture the current screen with full pixel value. Each pixel is represented in 32 bits and
BGRA format. However, this process may cause the flicking and tearing effect.
#define SCREEN_WIDTH 480
#define SCREEN_HEIGHT 272
uint32 screenshot[SCREEN_WIDTH*SCREEN_HEIGHT];
wr8(REG_SCREENSHOT_EN, 1);
for (int ly = 0; ly < SCREEN_HEIGHT; ly++) {
wr16(REG_SCREENSHOT_Y, ly);
wr8(REG_SCREENSHOT_START, 1);
//Read 64 bit registers to see if it is busy
while (rd32(REG_SCREENSHOT_BUSY) | rd32(REG_SCREENSHOT_BUSY + 4));
wr8(REG_SCREENSHOT_READ , 1);
for (int lx = 0; lx < SCREEN_WIDTH; lx ++) {
//Read 32 bit pixel value from RAM_SCREENSHOT
//The pixel format is BGRA: Blue is in lowest address and Alpha
is in highest address
screenshot[ly*SCREEN_HEIGHT + lx] = rd32(RAM_SCREENSHOT + lx*4);
}
wr8(REG_SCREENSHOT_READ, 0);
}
wr8(REG_SCREENSHOT_EN, 0);
Code Snippet 12 Screenshot with full pixel value
2.5.9 Performance
The graphics engine has no frame buffer: it uses dynamic compositing to build up each
display line during scan out. Because of this, there is a finite amount of time available to
draw each line. This time depends on the scan out parameters (REG_PCLK and
REG_HCYCLE) but is never less than 2048 internal clock cycles.
Some performance limits:
 The display list length must be less than 2048 instructions, because the
graphics engine fetches display list commands one per clock.
 The graphics engine performance rending pixels is 4 pixels per clock, for any
line with 2048 display commands the total pixels performance drawn must be
less than 8192.
 For some bitmap formats, the drawing rate is 1 pixel per clock. These are
TEXT8X8, TEXTVGA and PALETTED.
 For bilinear filtered pixels, the drawing rate is reduced to ¼ pixel per clock.
Most bitmap formats draw at 1 pixel per clock, and the above formats
(TEXT8X8, TEXTVGA and PALETTED) draw at 1 pixel every 4 clocks.