STM32F429 LTDC and SDRAM

[predrag10]

Posted on June 16, 2015 at 14:26

Is it possible to use internal RAM as a frame buffer for LTDC?

Where exactly in std lib examples are external RAM and LTDC connected? It seems to me that the code is written on SDRAM address but I cannot find any DMA/DMA2D initialization for sending data from SDRAM to LTDC controller.

Thank you!

#!stm32f4-disco #!stm32f4-disco #sdram #sdram #ltdc

[Tesla DeLorean]

Posted on June 16, 2015 at 14:44

/* LCD Size (Width and Height) */

#define  LCD_PIXEL_WIDTH    ((uint16_t)240)

#define  LCD_PIXEL_HEIGHT   ((uint16_t)320)

#define LCD_FRAME_BUFFER       ((uint32_t)0xD0000000)

#define BUFFER_OFFSET          ((uint32_t)0x50000)

STM32F429I-Discovery_FW_V1.0.1\Utilities\STM32F429I-Discovery\stm32f429i_discovery_lcd.h

STM32F429I-Discovery_FW_V1.0.1\Utilities\STM32F429I-Discovery\stm32f429i_discovery_lcd.c

[predrag10]

Posted on June 16, 2015 at 15:09

I've seen that and realize that writing to LCD to draw a char is writing to external RAM memory address i.e.

*(__IO uint16_t*) (CurrentFrameBuffer + (2*Xaddress) + xpos) = CurrentBackColor;

How is then the data converted from SDRAM to LTDC RGB pins?

Can I use internal SRAM memory instead of external SDRAM?

[waclawek.jan]

Posted on June 16, 2015 at 16:06

I don't use the LCD controller but if I read RM0090 right, the LCD controller is an AHB-matrix master and incorporates a DMA of its own. The framebuffer address is held in LTDC_LxCFBAR.

According to fig.2, the controller can master the FLASH, all the three SRAMs and the FMC controller.

JW

[predrag10]

Posted on June 16, 2015 at 16:14

Ok I've figured it out. You need to enter start address of LTDC Layer1 and/or Layer2:

LTDC_Layer_InitStruct.LTDC_CFBStartAdress = LCD_FRAME_BUFFER;

If you use external SDRAM you have level of abstraction and by writing on memory location 0xD0000000 or 0xC0000000 you are writing both on SDRAM and LTDC.

Thank you, guys!

[Tesla DeLorean]

Posted on June 16, 2015 at 16:46

Yes, you both have access to the frame buffer, from a user perspective you paint content there, and from the peripheral side is sits in a loop copying/streaming the data out in the prescribed format to the lines of the screen, over-and-over.

[predrag10]

Posted on June 16, 2015 at 21:18

Thanks Clive! For RAM space calculation is this OK approach: 320x240*18bits/8bits = 172,8kB of memory of 256kB total for 1 layer?