Interfacing (DSI, CSI, I2C, etc.) • Garbled UART console on Pi Zero W with PL011 (disable-bt) despite correct baudrate — buildroot custom image

Hi all,

I'm running a custom Buildroot (2026.02) image on a Raspberry Pi Zero W, booting directly (no U-Boot). UART console output is garbled/corrupted from the very first boot message onward — it never becomes readable, even after 30+ seconds.

Setup:
- Board: Raspberry Pi Zero W (BCM2835)
- Kernel: mainline linux (rpi fork), DTS - Terminal: (confirmed correct baudrate)
- USB-serial adapter on GPIO14 (TXD)/GPIO15 (RXD), 3.3V, wired crossed, common GND confirmed

config.txt (relevant parts, post-processed by build script):

cmdline.txt:

I intentionally disabled Bluetooth () to free up the full PL011 hardware UART on GPIO14/15, instead of the Mini-UART, specifically to avoid the classic mini-UART/VPU-clock baudrate drift issue.

What I've already tried:
- Confirmed terminal baudrate matches (115200 8N1)
- Added in addition to — no change
- Verified actually deployed to the boot partition matches source (post-image script confirmed working)
- Captured raw bytes directly from with : output is dominated by bytes with sparse single set bits (not random noise, not repeating printable-char garbage) — suggests receiver is oversampling relative to actual bit rate, i.e. sender's real baud rate is lower than expected 115200.

Question
Given PL011 is selected (not mini-UART) via , and are both set, what else determines the UART reference clock on the Zero W specifically? I'm about to try adding — has anyone confirmed this is still needed even with the full PL011 UART on BCM2835, or is there another firmware parameter I'm missing?

Any pointers appreciated — happy to post more logs/config if useful.

Statistics: Posted by Coolba — Sun Sep 13, 2026 7:10 am — Replies 0 — Views 16

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