ugfx/drivers/gdisp/STM32LTDC

Usage

To use this driver:

1. Add in your gfxconf.h: a) #define GFX_USE_GDISP GFXON

2. To your makefile add the following lines:

	include $(GFXLIB)/gfx.mk
	include $(GFXLIB)/drivers/gdisp/STM32LTDC/driver.mk

3. Add a board_STM32LTDC.h to you project directory (or board directory) based on one of the templates.

Limitations

Currently, both gOrientationPortrait and gOrientationLandscape are not supported by this driver.

Configuration

Configuration options available in gfxconf.h:

Option	Default	Description
STM32LTDC_DMA_CACHE_FLUSH	GFXOFF	Whether to flush the DMA cache on DMA2D operations. This will be turned on automatically on certian platforms/systems.
STM32LTDC_USE_DMA2D	GFXON	Whether to use the DMA2D peripheral for hardware acceleration.
STM32LTDC_USE_LAYER2	GFXOFF	Whether to use the 2nd LTDC layer. See the corresponding section below.
STM32LTDC_USE_DOUBLEBUFFERING	GFXOFF	Whether to use double buffering. See the corresponding section below.
STM32LTDC_USE_RGB565	GFXOFF	Whether to use RGB565 instead of RGB888.

2nd layer

To use the 2nd LTDC layer:

• set STM32LTDC_USE_LAYER2 to GFXON in gfxconf.h.
• set GDISP_TOTAL_DISPLAYS to 2 in gfxconf.h.

The 2nd layer is exposed as a separate display. Use gdispGetDisplay() to retrieve the individual layers.

For more information, see:

• https://wiki.ugfx.io/index.php/Multiple_displays#Example_-_Same_controller
• https://wiki.ugfx.io/index.php/Multiple_displays#Access_the_displays

Double buffering

To use double buffering:

• set STM32LTDC_USE_DOUBLEBUFFERING to GFXON in gfxconf.h.
• set GDISP_TOTAL_DISPLAYS to 2 in gfxconf.h.

When double buffering is enabled, the 2nd LTDC layer cannot be used. While this limitation is easy to remove from a software perspective, there is little benefit in doing so. Double buffering requires, as the name implies, twice the memory. If the 2nd layer would be used together with double buffering strategy, a total of four full framebuffers would be required. Years of real-world experience shows that there's practically never enough memory bandwidth available to do this.

To use double buffering in an application, retrieve the two buffers via gdispGetDisplay(). Whenever a buffer swap is necessary, use gdispGControl(g, STM32LTDC_CONTROL_SHOW_BUFFER, NULL); where g is the buffer to be shown.

Simple example:

#include "gfx.h"

static GDisplay* _display1;
static GDisplay* _display2;

// Requests a buffer swap on the driver level
static void _setActiveBuffer(GDisplay* g)
{
	gdispGControl(g, STM32LTDC_CONTROL_SHOW_BUFFER, NULL);
}

int main(void)
{
	// Initialize uGFX library
	gfxInit();
	
	// Get the two buffers
	_display1 = gdispGetDisplay(0);
	if (!_display1)
		gfxHalt("could not get display 1");
	_display2 = gdispGetDisplay(1);
	if (!_display2)
		gfxHalt("could not get display 2");

	// Render to each buffer
	gdispGClear(_display1, GFX_BLUE);
	gdispGClear(_display2, GFX_RED);

	// Switch between buffers
	while (gTrue) {
		gfxSleepMilliseconds(800);
		_setActiveBuffer(_display1);
		gfxSleepMilliseconds(800);
		_setActiveBuffer(_display2);
	}

	return 0;
}