Enabling Timer on STM32H747I-DISCO (CM4 or CM7) Causes LCD to Go Blank — What Could Be the Issue?

[Shealtiel]

I'm using the STM32H747I-DISCO board. When I enable any timer (e.g., TIM3, TIM4) on either CM4 or CM7, the LCD display goes blank or stops updating. The display works fine until the timer is initialized.

• I'm using TouchGFX on CM7.
• Display is initialized correctly at startup.
• The issue appears right after initializing the timer via HAL.

Could this be due to a conflict with LTDC clocks, TouchGFX timing, or backlight control (PWM)? How can I safely use a timer without affecting the display?

Any insights or configuration tips would be appreciated.

[Ozone]

You would need to show the code associated with this timer(s), especially initialisation and interrupt handling routines (including callbacks).
And check if TouchGfx uses some of those timers already.

I'm not a H7 / TOuchGfx user, so I can only give general hints.

[Shealtiel]

Thank you for the suggestions!

I’ve checked the CM7 code (which runs TouchGFX), and it does not use any timers explicitly only the default system clock and LTDC setup. However, when I enable certain timers (like TIM3 or TIM4) on CM4, the LCD on CM7 goes blank or stops updating.

This happens even if CM7 never touches those timers. So I suspect it could be a shared clock source issue, or maybe the CM4 initialization is interfering with something used by LTDC (like a PLL or peripheral clock domain).