samples: subsys: input: draw_touch_events: BUS FAULT on STM32U5G9J-DK1 + st_lcd_dsi_mb1835

[CharlesDias]

Describe the bug

On the STM32U5G9J-DK1 with st_lcd_dsi_mb1835, the sample becomes stuck, and a "strange" image is displayed on the screen. No output log.

The BUS FAULT message is printed out when the sample is rerun with the CONFIG_LOG_MODE_IMMEDIATE enabled.

!*** Booting Zephyr OS build v4.1.0-15211-g47a20f60d09a ***
[00:00:00.637,000] <inf> sample: Touch sample for touchscreen: st1633i@70, dc: display-controller@40016800
<err> os: ***** BUS FAULT *****
<err> os:   Precise data bus error
<err> os:   BFAR Address: 0x0
<err> os: r0/a1:  0x200e15b8  r1/a2:  0x00000000  r2/a3:  0x00000000
<err> os: r3/a4:  0x00000000 r12/ip:  0x00000000 r14/lr:  0x08005e53
<err> os:  xpsr:  0x6100020f
<err> os: Faulting instruction address (r15/pc): 0x08005c96
<err> os: >>> ZEPHYR FATAL ERROR 25: Unknown error on CPU 0
<err> os: Fault during interrupt handling

<err> os: Current thread: 0x200e1418 (unknown)
<err> os: Halting system

Additionally, if the SCREEN_WIDTH_TO_CROSS_DIM value is changed to 20, the FAUL does not occur; instead, it shows only a horizontal line, rather than a cross.

Regression

• This is a regression.

Steps to reproduce

1. Apply the patch boards: shields: st: enable the touch input on st_lcd_dsi_mb1835 #98717
2. Compile and flash the sample west build -p -b stm32u5g9j_dk1 --shield st_lcd_dsi_mb1835 samples/subsys/input/draw_touch_events

Relevant log output

!*** Booting Zephyr OS build v4.1.0-15211-g47a20f60d09a ***
[00:00:00.637,000] <inf> sample: Touch sample for touchscreen: st1633i@70, dc: display-controller@40016800
<err> os: ***** BUS FAULT *****
<err> os:   Precise data bus error
<err> os:   BFAR Address: 0x0
<err> os: r0/a1:  0x200e15b8  r1/a2:  0x00000000  r2/a3:  0x00000000
<err> os: r3/a4:  0x00000000 r12/ip:  0x00000000 r14/lr:  0x08005e53
<err> os:  xpsr:  0x6100020f
<err> os: Faulting instruction address (r15/pc): 0x08005c96
<err> os: >>> ZEPHYR FATAL ERROR 25: Unknown error on CPU 0
<err> os: Fault during interrupt handling

<err> os: Current thread: 0x200e1418 (unknown)
<err> os: Halting system

Impact

Annoyance – Minor irritation; no significant impact on usability or functionality.

Environment

No response

Additional Context

No response

[CharlesDias]

Fixed on:

• samples: subsys: input: draw_touch_events: fix overflow in clear_screen loop #98719

[CharlesDias]

After further investigation, I found that the BUS FAULT was caused by the clear_screen loop writing past the framebuffer. When CROSS_DIM does not evenly divide the panel WIDTH/HEIGHT, the last tile on the right/bottom extends beyond the framebuffer row/column.

Backtrace

#12 0x0800a3ea in memcpy ()
#13 0x08007ece in stm32_ltdc_write (dev=<optimized out>, x=<optimized out>, y=<optimized out>, desc=0x20000000 <buf_desc>, buf=0x800aff4 <buffer_cross_empty>) at /home/charlesdias/zephyrproject/zephyr/drivers/display/display_stm32_ltdc.c:233
#14 0x0800056e in display_write (buf=0x800aff4 <buffer_cross_empty>, desc=0x20000000 <buf_desc>, y=190, x=399, dev=<optimized out>) at /home/charlesdias/zephyrproject/zephyr/include/zephyr/drivers/display.h:288
#15 clear_screen () at /home/charlesdias/zephyrproject/zephyr/samples/subsys/input/draw_touch_events/src/main.c:93
#16 0x08000694 in main () at /home/charlesdias/zephyrproject/zephyr/samples/subsys/input/draw_touch_events/src/main.c:156

Solution:
For each x,y tile, it now creates a local descriptor with:

• width = min(CROSS_DIM, WIDTH - x)
• height = min(CROSS_DIM, HEIGHT - y)
• pitch remains CROSS_DIM (source stride in pixels)
• buf_size = width * height * BPP

This guarantees we never copy past the framebuffer boundaries for tiles at the right/bottom edges.

Additional fix (pixel format)
Additionally, the zephyr_lcd_controller pixel-format did not match the driver configuration, which expects PANEL_PIXEL_FORMAT_ARGB_8888.

Solution (pixel format)
Set the zephyr_lcd_controller pixel-format to PANEL_PIXEL_FORMAT_ARGB_8888 to match the driver configuration.