I can confirm that the ETRX357USB-LRS+8M can be flashed with an appropriate EZSP firmware without the use of any programming hardware.
So, without any guarantees (you might -but probably won’t- brick your device), here’s how:
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Download the firmware. I used some random blob someone put on github that at least seemed to have the right name. What could possibly go wrong, right?
https://github.com/yqyunjie/Zigbee-Project/blob/master/firmware/EmberZNet/EM35x-EZSP/build/em35x-ezsp-images/EM357/em357-ncp-uart-xon-xoff-use-with-serial-uart-bl-500.ebl?raw=true
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(Install USB-to-serial drivers for the device. Linux will load the driver automatically when you plug in; not sure about other OSes.)
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Install a serial port communication app that supports X-MODEM. (debian/ubuntu: sudo apt-get install minicom) Run it and configure it (sudo minicom -s) to use the fake serial port (/dev/ttyUSB0) at 19200 baud 8N1. Disable both hardware (RTS/CTS) and software (XON/XOFF) flow control.
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Type ‘AT’ , you should get OK in response. Now type ‘AT+BLOAD’ . The device will reboot into the bootloader.
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Change the baud rate in the serial port communication app setting to 115200 baud. (exit minicom using CTRL-A Q, run ‘sudo minicom -s’ again)
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Pressing enter in the terminal should now show you a three-option boot loader menu. Choose option 1.
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‘C’ characters will start showing. Don’t wait for this to finish, but start an X-MODEM upload of the firmware you downloaded earlier (use CTRL-A S in minicom). You have 60 seconds to start the upload.
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After the upload finished, you should return to the menu. Now select option 2, to reboot into the new firmware. You’re done.
Enjoy!