I have a “Banana Pi BPI-R4 Pro 8X (MT7988A, 8GB RAM)” The board powers on normally, but I get absolutely no output from the serial console during power-on or reset.
Setup:
Debug console: correct USB-C Debug Console port Boot switch: SW3 A=1, B=1 (SD boot) Serial: 115200 8N1, no flow control SD card tested/removed; issue remains PWR green LED is ON Other LEDs (R/B/W2G/W5G/W6G) also illuminate
Linux detects the onboard USB-UART correctly HOLTEK USB TO UART BRIDGE ID: 04d9:b534 /dev/ttyACM0 fuser /dev/ttyACM0` shows nothing using the port. I tested with: sudo picocom -b 115200 /dev/ttyACM0 and also: sudo cat /dev/ttyACM0
Then power-cycled and pressed RESET, but no characters appear at all — not even the expected early boot ROM messages such as F0:, FA:, or Jump to BL.
Things I have already tried
Correct USB-C Debug Console port
115200 8N1
No hardware/software flow control
SW3 set to 1,1 for SD boot
SD card inserted
SD card removed
Full power cycle
RESET button
picocom
cat /dev/ttyACM0
Verified that no other process is using /dev/ttyACM0
Verified the Holtek USB-UART bridge is correctly detected by Linux
My main questions
- What could cause the BPI-R4 Pro to produce absolutely no output on the Debug Console even though the board is powered on?
- Is it possible that the board is actually booting normally despite producing no UART output?
- If the board can boot without UART output, what is the best way to verify that the boot process is actually working?
- Is there a way to verify whether the MT7988A BootROM is running without relying on the onboard USB-UART console?
- What is the correct hardware-level UART test point/pin for the MT7988A debug UART on the BPI-R4 Pro 8X?
- Can I safely connect my 3.3 V PL2303 USB-TTL adapter directly to the debug UART? If so, which exact TX and GND pins should I use?
- Are there any LED patterns, Ethernet link behavior, SD-card activity, or other indicators that can confirm whether the board has successfully reached U-Boot/OpenWrt when the serial console is silent?
- Is there a recommended recovery procedure for the BPI-R4 Pro if the Debug Console remains completely silent?
- Could a bad bootloader, incorrect boot configuration, eMMC/NAND state, or SD-card image cause the Debug Console to remain completely blank from the very beginning?
Note :- i am just testing so i have not even tried to used my own firmware just using the one provided on Banana pi website.