Uctronics offers several versions of 3.5-inch LCD screen, with SPI and HDMI interfaces, with different enclosures etc. Make sure that you buy exactly this version (SPI with acrylic case and stylus):
https://www.uctronics.com/display/uctronics-3-5-inch-touchscreen-for-raspberry-pi-with-case.html
To install the driver, clone exactly this repository:
https://github.com/UCTRONICS/UCTRONICS_HSLCD35
and execute Raspbian/install_driver.sh script (it will require reboot at the end).
It is also important, that your initial Raspbian image has compatible kernel version - one from these.
Image 2021-05-07-raspios-buster-armhf-lite.zip
(torrent) has kernel version 5.10.17-v7+, which is good.
Do NOT upgrade it after installing, as it would stop the display from working. Instead, after installing the display, execute:
apt-mark hold raspberrypi-kernel
which will prevent the kernel from being upgraded in the future. Security-wise, doing so is a bad idea, but it is necessary for this display to work, since its drivers are linked only with particular kernel versions (source code is not provided).
Do NOT follow these instructions, as they are related to different model, and despite of not working, will also install very old kernel version, with security bugs:
- https://github.com/UCTRONICS/UCTRONICS_LCD35_RPI
- https://www.uctronics.com/wiki/(SKU:_U4703)UCTRONICS_LCD35_RPI_(SPI_interface)
This is a framebuffer-based driver. It works in a different way (much slower) than native drivers. On each operation:
- empty image is created
- all texts (current and all previous ones) are drawn on this image
- image is saved to filesystem
- image contents are copied to framebuffer by
fbitool