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David Gwilliam
2026-02-12 00:45:31 -08:00
commit 5f168f370b
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libraries/PNGdec/examples/dma_perf_boost/dma_perf_boost.ino Normal file
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//
// Example sketch showing the performance benefit of using
// DMA when pushing pixels to serial connected LCD displays
//
// written by Larry Bank (bitbank@pobox.com)
// Febrary 27, 2025
//
#include <PNGdec.h>
#include <bb_spi_lcd.h>
#include "../../test_images/octocat.h"
PNG png;
BB_SPI_LCD lcd;
int w, h, xoff, yoff;
bool bDMA;
static uint16_t usPixels[320]; // make sure there is enough room for the full image width
//
// PNG draw callback
// Called with a full row of pixels
// for every row in the image
//
int PNGDraw(PNGDRAW *pDraw)
{
if (pDraw->y == 0) {
// set the address window when we get the first line
lcd.setAddrWindow(xoff, yoff, w, h);
}
// There's a risk of overwriting pixels that are still being sent to the display if we only use a single \
// DMA buffer, **BUT** in this case, the PNG decoding plus the pixel conversion takes a long time
// relative to sending pixels to the display. If the display were a REALLY slow one, then it would be
// prodent to use a dual (ping-pong) buffer scheme to avoid that risk.
png.getLineAsRGB565(pDraw, usPixels, PNG_RGB565_BIG_ENDIAN, 0); // get help converting to RGB565
if (bDMA) {
lcd.pushPixels(usPixels, pDraw->iWidth, DRAW_TO_LCD | DRAW_WITH_DMA);
} else {
lcd.pushPixels(usPixels, pDraw->iWidth);
}
return 1;
} /* PNGDraw() */
void setup()
{
long lTime;
lcd.begin(DISPLAY_CYD_543 /*DISPLAY_WS_AMOLED_18*/);
lcd.fillScreen(TFT_BLACK);
lcd.setFont(FONT_12x16);
lcd.setTextColor(TFT_GREEN);
lcd.setCursor((lcd.width() - 17*12)/2, 0);
lcd.print("PNG DMA Perf Demo");
png.openFLASH((uint8_t *)octocat, sizeof(octocat), PNGDraw);
w = png.getWidth();
h = png.getHeight();
xoff = (lcd.width() - w)/2; // center on the LCD
yoff = (lcd.height() - h)/2;
bDMA = false; // first time without DMA
lTime = micros();
png.decode(NULL, PNG_FAST_PALETTE); // use the RGB565 palette to speed up color conversion for the LCD
lTime = micros() - lTime;
png.close();
lcd.setCursor((lcd.width() - (20*12))/2, lcd.height()-32);
lcd.printf("Without DMA: %d us\n", (int)lTime);
png.openFLASH((uint8_t *)octocat, sizeof(octocat), PNGDraw);
w = png.getWidth();
h = png.getHeight();
xoff = (lcd.width() - w)/2; // center on the LCD
yoff = (lcd.height() - h)/2;
bDMA = true; // second time with DMA
lTime = micros();
png.decode(NULL, PNG_FAST_PALETTE); // use the RGB565 palette to speed up color conversion for the LCD
lTime = micros() - lTime;
png.close();
lcd.setCursor((lcd.width() - (17*12))/2, lcd.height()-16);
lcd.printf("With DMA: %d us\n", (int)lTime);
}
void loop()
{
}