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LN882H UART flashing protocol documentation - Windows LN882H flasher with fast flash read

p.kaczmarek2 2166 33

TL;DR

  • LN882H flashing protocol documentation covers a WiFi & BT Wireless ARM Cortex-M4F SoC, its UART bootloader flow, and a Windows flasher for backup, erase, write, and terminal mode.
  • The process loads a RAM code over YModem, then uses plain-text ASCII commands for flash operations, while flash data transfer and the newer read path use raw binary.
  • The chip prints an identity string at 115200 baud, and the bundled scripts include sample_dump_at_baud_460800.bat for faster firmware reads.
  • Flash dump was optimized from slow ASCII text output to raw bytes with 16-bit CRC checking, improving read speed and reliability.
  • LN882H must be put in bootloader mode by grounding a specific pin before rebooting, or the flashing tools cannot connect.
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  • #31 21622229
    p.kaczmarek2
    Moderator Smart Home  
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    Which bytes can change between reboots?
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  • #32 21622233
    divadiow
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    Well. I dunno but when I kept it in boot mode between dumps, so no app boot, the bytes were identical.

    Added after 25 [minutes]:

    I'll do read tests again. If that user's device didn't boot up in between then that would be an issue
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  • #33 21622289
    p.kaczmarek2
    Moderator Smart Home  
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    But the read does CRC check, as implemented by @insmod. So there should be no errors...
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  • #34 21622390
    divadiow
    Level 38  
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    to remove any doubt:

    Tuya_3.5.4_FEIT_Chasing_FETAP20CAN_(schemaID-fxxrjk)_LN882H_1.0.18.bin to blank LN882H

    115200 - done in 184.0235767s
    230400 - done in 92.9656231s
    460800 - done in 47.4550467s
    921600 - done in 24.7300339s

    A9 low throughout

    Code: Text
    Log in, to see the code


    Dialog box with message “The chosen files are identical” and “OK” button
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Topic summary

✨ The LN882H is a WiFi and Bluetooth wireless System on Chip (SoC) based on the ARM Cortex-M4F core, commonly used in IoT devices. It supports a UART-based flashing protocol for firmware updates and flash memory access. The protocol uses simple ASCII commands for control, while the actual flash data transfer employs the YModem protocol. To initiate flashing, the LN882H must be placed into bootloader mode by grounding a specific pin and rebooting the device. Upon entering bootloader mode, the LN882H outputs a default identity string at 115200 baud rate, which can be monitored to confirm readiness. This UART flashing method facilitates firmware development and modification by enabling read and write operations on the device's flash memory.
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FAQ

TL;DR: Switching the LN882H flash dump from ASCII (3 bytes/byte) to raw 514-byte binary packets delivers a 3× throughput boost; "it's finally fast enough to back up a 2 MB image in under a minute" [Elektroda, p.kaczmarek2, post #21612706]

Why it matters: Faster, checksum-verified transfers slash debug and backup time.

Quick Facts

• Default bootloader speed: 115 200 bps [Elektroda, p.kaczmarek2, post #21612706] • Highest tested speed: 921 600 bps with stable CRC [Elektroda, p.kaczmarek2, post #21612706] • Packet size in fast dump: 512 data + 2 CRC bytes [Elektroda, p.kaczmarek2, post #21612706] • Full-chip erase command: ferase_all (≈2 MB in one call) [Elektroda, p.kaczmarek2, post #21612706] • Windows GUI flasher size: 1.6 MB executable [GitHub Releases, 2025]

How do I enter the built-in bootloader?

Ground the designated BOOT pin, then reset or power-cycle the board; the chip greets at 115 200 bps with a timestamp string [Elektroda, p.kaczmarek2, post #21612706]

What commands does the RAM loader understand?

Key ASCII commands: ferase, ferase_all, fdump, upgrade, startaddr, baudrate, reboot, version, flash_info, flash_uid [Elektroda, p.kaczmarek2, post #21612706]

Can you outline the three-step dump procedure?

  1. Load the modified RAM dumper (baud patched to your target rate).
  2. Issue "fdump 0x0 raw".
  3. Receive data and verify each block’s CRC before saving. "Three lines, three clicks" [Elektroda, p.kaczmarek2, post #21612706]

How is baudrate changed on-the-fly?

The tool edits specific bytes inside the 8 kB RAM loader image before upload, so the MCU reinitialises UART at 115 200–921 600 bps without extra commands [Elektroda, p.kaczmarek2, post #21612706]

What happens if the CRC check fails?

The PC side stops reception and reports "CRC FAIL" with the offending address; resending that block usually fixes noise-induced errors [Elektroda, p.kaczmarek2, post #21612706]

How do I flash new firmware from Windows?

Run SharpLN882HTool, choose sample_write.bat, which: 1) sets baud to 921 600 bps, 2) sends startaddr 0x0, 3) issues upgrade, then 4) pushes the .bin via YModem [Elektroda, p.kaczmarek2, post #21612706]

Is there a GUI alternative?

Yes, a pre-built 1.6 MB Windows executable is on GitHub; future releases will merge into Easy Flasher for one-click updates [GitHub Releases, 2025].
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