FAQ
TL;DR: A NiceMCU XH-WB3S board (BK7238, 2 MB flash) can run OpenBeken if you erase the whole SPI and re-flash with a CRC-fixed 7238 image; boards cost ≈ US $1.50 each and need >300 mA during Wi-Fi start-up. “Boot loops usually mean undervoltage” [Elektroda, insmod, post #21562748]
Why it matters: Correct flashing and stable power prevent endless reboots and CRC errors.
Quick Facts
• Chipset: BK7238, ARM Cortex-M33, 160 MHz [Elektroda, divadiow, post #21440151]
• On-board flash: 2 MB (ID 0x852015) [Elektroda, divadiow, post #21289375]
• Dev-board price: US $1–1.5 on AliExpress [Elektroda, insmod, post #21327474]
• Recommended supply: 3.3 V @ ≥350 mA during TX bursts [*BK72xx DS*]
• Default UART: 115 200 bps on P0 (UART2) [Elektroda, divadiow, post #21442320]
Why do I get endless CRC-mismatch errors when flashing?
The GUI flasher lacked the Puya 25Q16HB (ID 0x152085) entry, so the chip stayed write-protected and every sector verify failed. Update to BK7231GUIFlashTool ≥v1.9.21 or add the ID manually, then erase and re-flash [Elektroda, p.kaczmarek2, post #21342531]
Which firmware file should I use for the XH-WB3S board?
Use OpenBK7238_QIO_x.xx.xx.bin (or the .rbl OTA file) because the module really contains a BK7238, not a BK7231 [Elektroda, DeDaMrAz, post #21542280]
The board reboots every few seconds—why?
A reboot loop with only the RT-Thread banner usually means the 3.3 V rail dips below 3.0 V when Wi-Fi starts. Provide a stable ≥350 mA source or add a 470 µF capacitor [Elektroda, insmod, post #21562748]
How do I force the bootloader to accept my image?
Check “Overwrite bootloader” in the GUI, flash the CRC-fixed QIO image, then reset. On BK7238 the bootloader sits at 0x0 and refuses un-CRC’d binaries [Elektroda, divadiow, post #21550671]
What is the “No TLV header found in flash” message?
It comes from the SDK’s RF-calibration code; the first boot notices that the RF OTP/TLV partition is empty, writes defaults, then continues. The notice is harmless [Elektroda, p.kaczmarek2, post #21564311]
Why does my custom MAC vanish after reboot?
BK7238 stores the MAC in the RF-OTP/TLV area. Current OpenBeken writes it to config only; on the 7238 it must be written with manual_cal_write_macaddr_to_flash(). Until patched, the chip reloads the factory MAC on cold boot [Elektroda, p.kaczmarek2, post #21564311]
How can I enter Safe-Config mode if AP never appears?
Press or toggle RESET five times within 5 s; the bootloader starts OBK in SafeConfig, creating AP “OpenBK_xxxxxx” even with invalid Wi-Fi data [Elektroda, divadiow, post #21550706]
Power-meter readings jump by 20 V—bug or feature?
Voltage spikes on BL0937 driver occur when heavy logging or MQTT runs. Disable verbose logs (loglevel 0) or MQTT to stabilise readings [Elektroda, insmod, post #21520958]
Fast-Connect flag—what does it do?
FastConnect 1 skips full scan and uses stored BSSID/PSK. It cuts connect time from ≈3 s to 300 ms and saves ≈80 mA∙s per wake-up [Elektroda, insmod, post #21507260]
I only see garbage on UART—correct pins?
UART2 TX (module P0) outputs OBK logs at 115 200 bps. Connect RX of your adapter to P0, 3.3 V tolerant [Elektroda, divadiow, post #21550104]
Edge case: What if I flashed a BK7231 image to BK7238?
The chip shows only the bootloader banner and reboots; re-flash the correct 7238 QIO binary or full 2 MB dump via SPI [Elektroda, divadiow, post #21342237]
3-step How-To: Recover a soft-bricked XH-WB3S
- Erase full 0-0x1FFFFF with BKFIL (SPI needed if UART locked). 2. Flash OpenBK7238_QIO_x.bin at 0x0 with “Overwrite bootloader”. 3. Reset; join AP and finish setup—done.
