Development tools for Zephyr on STM32Workbench for Zephyr: VS Code extension to set up, build, flash and debug Zephyr applications on STM32.Devicetree manager: browse, edit and visualize Zephyr devicetree, STM32CubeMX-like for Zephyr.
I had issues with Eclipse Mars too, So I switched to Luna and everything is working as it should.
However I am using the STM32F429I-discovery board (LCD version.