ST7735-VideoPlayback-STM32

A library for smooth video playback on a ST7735 display. It uses an SD card module for video storage. The library can be used to streams videos at 33-35FPS.

Showcase

Watch the Showcase on Youtube:

Pinout

ST7735 Display:

Display Pin	Connection
LED (Backlight)	5V
SCK (CLK)	SPI1_SCK
SDA	SPI1_MOSI
DC (Data/Command)	PA9
RESET	PC7
CS (Chip Select)	PB6
GND	GND
VCC	5V

SD Card Module:

SD Module Pin	Connection
SD_CS	PB1
SD_MOSI	SPI2_MOSI
SD_MISO	SPI2_MISO
SD_SCK	SPI2_SCK

If you are using the on-display SD card module, VCC and GND are used from the display pin connections.

Usage

TBD:

• CubeMX steps
• Pinout connections
• Sources copy
• Compiling the code
• Video binary generation
• SD card formatting + vid/ directory
• Flash the code and run

Video Conversion Script

The python script is located at video_converter/video_converter.py. It is used to convert a video file to the usable video binary format.

The output binary video.bin is generated in video_converter/video_output.

$ python video_converter.py -h
usage: video_converter.py [-h] [--start START]
                          [--end END] [--landscape]
                          video_input

Convert video to binary format for display.

positional arguments:
  video_input    Path to input video

options:
  -h, --help     show this help message and exit
  --start START  Start time MM:SS
  --end END      End time MM:SS
  --landscape    Use landscape mode for display

Video Format

The video binary follows the below format. This section can be used as a reference for debugging video and frame information.

The file consists of a header followed by per frame data.

Header:
[video_width HB][video_width LB][video_height HB][video_height LB][num_frames HB][num_frames LB]

Per Frame:
['F']['R']['M'][Pixel Data ...]

Pixel Format:
- Each pixel color is 2 bytes in RGB565 form:
[RGB565 Color HB][RGB565 Color LB]

Here,

• HB - Higher byte
• LB - Lower byte

Optimizations

• Using DMA for SD TX and RX.
• Using DMA for ST7735 Display TX.
• Modified FATFS User SPI drivers to allow multi-byte SPI TransmitReceive.
• Using prescaler=2 for SD reading in FCLK_FAST.

Current per-frame timing information:

Frame read time: ~22ms
Frame draw time: ~8ms

Possible optimizations:

• RLE (Run length encoding) and dirty rectangles implementation. (with thresholds to reduce per frame CPU overhead)

Notes

• Mounting/Interfacing the SD card can be nasty over SPI, by giving errors multiple times.
  • Make sure that the SD pins were set to pull-up in CubeMX. See this for reference.
  • Make sure all the connections to the SD card are tight.
  • Try reducing FCLK_SLOW and FCLK_FAST prescalers by using the prescalers specified here.

Libraries Used

• FATFS
• cubeide-sd-card for the FATFS User SPI drivers
• stm32-st7735
• LVGL's Image Converter

References

• ST7735 Datasheet