Touchgfx compatibility

[jijomathew]

hello,

 I am working on a project where I need to display a Touch GFX frame buffer on an OLED display that supports only 8-bit data transfers. The Touch GFX frame buffer is in RGB565 format (16-bit), while the OLED expects 8-bit data chunks for communication over SPI. I'm using an STM32 microcontroller and an SSD1333 display controller.

My setup.

• Microcontroller: STM32L4 series
• Display: OLED with SSD1333 controller (RGB565, 8-bit transfer)
• Framebuffer: 16-bit RGB565 from Touch GFX
• Communication: SPI 

  How can I split or convert the 16-bit RGB565 frame buffer data from Touch GFX into 8-bit chunks to properly send it to the OLED using SPI? Is there a specific function or method in Touch GFX that facilitates this kind of transformation?

  uint8_t Display_Frame_15_[] = {
  
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  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  
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  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x08, 0x00, 0x38, 0x61, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  
  0x00, 0x00, 0x00, 0x00,....}

  This is the image buffer that OLED drive demands ,pixel is 160*128

[unsigned_char_array]

---

@jijomathew wrote:
Microcontroller: STM32L4 series

---

Which one?

---

@jijomathew wrote:

• How can I split or convert the 16-bit RGB565 frame buffer data from Touch GFX into 8-bit chunks to properly send it to the OLED using SPI? Is there a specific function or method in Touch GFX that facilitates this kind of transformation?

---

Here are the functions you need to adapt to your Display:

https://support.touchgfx.com/docs/development/touchgfx-hal-development/scenarios/scenarios-spi

What data conversion is needed depends on your display and driver. You might need to swap byte order and/or bit order.
First write a driver for your display:

• Display init()
• Display clear()
• Display setCursor(x,y)
• Display writeData(data, numberOfPixels)
• Display writePixel(x,y,color) // only for testing, too slow for actual use

Then write a simple test program (use a for-loop to put a few rectangles of different colors on the display).

You might be able to use the DMA to do the SPI transfers to speed up your program.

If that works adapt the TouchGFX functions so it uses your driver.

@MM..1mentioned partial framebuffers. Read about partial framebuffers here: https://support.touchgfx.com/docs/development/scenarios/lowering-memory-usage-with-partial-framebuffer

[MM..1]

Too read about TouchGFX partial framebuffer mode. And you little mix 8bit is paralel mode vs SPI no paralel bus...

[jijomathew]

I have already integrated Touch GFX and the driver I am using takes input in the form of uint8_t. The driver function for drawing a bitmap is: 

HAL SPI Transmit(&hspi3, (uint8_t*) image, 40960, 10);

However, the Touch GFX frame buffer is in constant uint16_t* format, accessed via the get client frame Buffer(); function. To match the driver input, I typecast the framebuffer to constant uint8_t*:

(constant uint8_t*) get client frame buffer();

Despite this, the image displayed on the OLED screen appears distorted. I suspect the issue lies in the way the 16-bit frame buffer is being handled by the driver, as it expects 8-bit data.

Can you please help me understand the cause of this distortion and suggest the best approach to resolve it?

[unsigned_char_array]

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@jijomathew wrote:

However, the Touch GFX frame buffer is in constant uint16_t* format, accessed via the get client frame Buffer(); function. To match the driver input, I typecast the framebuffer to constant uint8_t*:

---

Typecasting a pointer won't change the data.
You probably need to change byte order.
You do this by modifying the original buffer or by creating a separate buffer with the converted values.
Some L4 models contain hardware acceleration (chromart) that can potentially help with this. But since you refused to answer my question I don't know what model you have.

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@jijomathew wrote:

the OLED screen appears distorted.

---

Please upload a photo of this.

[jijomathew]

The model is L496ZG 

[MM..1]

Primary question is your LCD SPI mode 3wire or 4wire? You show sending 8bit , then seem 4wire, but check.

[jijomathew]

[unsigned_char_array]

Looks like color bits are mixed up. What's the original image? Perhaps you can try a different test image such as a rainbow.

[MM..1]

How to change TouchGFX FrameBuffer to Big Endian? - STMicroelectronics Community