adding support for the ST7796 + creating a new variant of the T-beam

[Nasimovy]

modified the existing library for the ST7789 to support the ST7796
created a new variant of the T-beam that supports the ST7796 shield

edit:
the touchscreen is not working yet, the address has been added to the scani2c, should i separate it?

🤝 Attestations

• I have tested that my proposed changes behave as described.
• I have tested that my proposed changes do not cause any obvious regressions on the following devices:
  • LilyGo T-Beam

[Nasimovy]

converted it to draft because i seem to get SPI related errors

[caveman99]

Looking good overall, though i'd prefer if you got the touchscreen working as well

[Nasimovy]

im trying lower SPI speeds for both the LORA module and the display because it looks like the tbeam is very EMI susceptible, or the ST7796 pumps out loads of EMI.

yesterday i had a SPI related error every ~20 minutes, also next to zero Bluetooth reception

i first want to resolve that issue before i start implementing the touchscreen

edit: resolved, Bluetooth reception is resolved with higher pinheaders

[Copilot]

Pull Request Overview

Adds support for the ST7796 display and a matching T-Beam variant, plus a new CST226SE touchscreen driver.

• Define ST7796 pin mappings, dimensions, and backlight settings in variants/tbeam/variant.h
• Introduce a tbeam-displayshield PlatformIO environment with ST7796 and touchscreen library dependencies
• Update conditional compilation in display setup, NodeDB, and I2C scanning—and add TouchScreenCST226SE driver

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
variants/tbeam/variant.h	ST7796 macros and screen parameters
variants/tbeam/platformio.ini	New env with USE_ST7796 flag and lib_deps
src/mesh/NodeDB.cpp	Include USE_ST7796 in default-config screen check
src/main.cpp	Add USE_ST7796 to setup guards and CPU speed logic
src/input/TouchScreenCST226SE.h	New CST226SE touchscreen interface declaration
src/input/TouchScreenCST226SE.cpp	Implementation of CST226SE touchscreen handling
src/graphics/images.h	Extend image conditions to include USE_ST7796
src/graphics/ScreenFonts.h	Include USE_ST7796 in font-size guard
src/graphics/Screen.h	Add #include <ST7796Spi.h> for the new driver
src/graphics/Screen.cpp	Instantiate ST7796Spi, backlight and cleanup logic
src/detect/ScanI2CTwoWire.cpp	Detect CST226SE in I2C scan sequence
src/detect/ScanI2C.h	Add CST226SE to DeviceType enum
src/configuration.h	Define CST226SE_ADDR and CST226SE_ADDR_ALT

Comments suppressed due to low confidence (1)

src/input/TouchScreenCST226SE.cpp:21

• [nitpick] Consider adding unit or integration tests for the CST226SE driver initialization and touch event handling to ensure the new touchscreen code is covered and behaves as expected.

void TouchScreenCST226SE::init()

[mverch67]

I think using lovyanGFX (TFTDisplay.cpp) would have saved some work as it natively supports the ST7796 display driver and also the CST226 touch screen driver (in its develop branch). It would have allowed smoother integration into TFTDisplay.cpp and avoided some code duplication for the touch driver (e.g. onEvent()) as it would have been handled automatically by class TouchScreenImpl1. As a benefit screen powersave functions could have been inherited as well.

[Nasimovy]

I think using lovyanGFX (TFTDisplay) would have saved some work as it natively supports the ST7796 display

lovyangfx makes the program to large to fit on the t-beam (iram overflow ~2700)

edit: maybe i'm stupid but i got the display working in the arduino ide with lovyangfx but i couldn't fit it in the meshtastic code.

[mverch67]

lovyangfx makes the program to large to fit on the t-beam (iram overflow ~2700)

The current tbeam size in master is:

RAM:   [=         ]   7.4% (used 96820 bytes from 1310720 bytes)
Flash: [========= ]  89.3% (used 2165385 bytes from 2424832 bytes)

I wouldn't expect lovyanGFX being that large (260kB)?!

[Nasimovy]

lovyangfx makes the program to large to fit on the t-beam (iram overflow ~2700)

The current tbeam size in master is:

RAM:   [=         ]   7.4% (used 96820 bytes from 1310720 bytes)
Flash: [========= ]  89.3% (used 2165385 bytes from 2424832 bytes)

I wouldn't expect lovyanGFX being that large (260kB)?!

the IRAM is insufficient by 2736 bytes

/root/.platformio/packages/toolchain-xtensa-esp32/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld: .pio/build/tbeam-displayshield/firmware.elf section `.iram0.text' will not fit in region `iram0_0_seg'
/root/.platformio/packages/toolchain-xtensa-esp32/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld: IRAM0 segment data does not fit.
/root/.platformio/packages/toolchain-xtensa-esp32/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld: region `iram0_0_seg' overflowed by 2736 bytes

edit: if i compile the exact same code with 1 modification it fits on a esp 32S3