27. June 2020

ESP32 erase_flash failed with “Invalid head of packet”

The first step before installing MicroPython to ESP32 is to erase the flash.

I’ve installed all necessary software like esptool, but the flashing was failing with error:

esptool.py --chip esp32 --port /dev/ttyUSB0 erase_flash                                                                                                         ──(Sat,Jun27)─┘
esptool.py v2.8
Serial port /dev/ttyUSB0

A fatal error occurred: Failed to connect to ESP32: Invalid head of packet (0x1B)

The solution to the problem is to pres and hold BOOT button. Then start erase command mentioned above.

After the initial erase I was able to flash there MicroPython:

esptool.py --chip esp32 --port /dev/ttyUSB0 --baud 460800 write_flash -z 0x1000 esp32-idf4-20200627-unstable-v1.12-590-g9f911d822.bin

Then it was possible to connect via rshell:

rshell -p /dev/ttyUSB0                                                                                                                                          ──(Sat,Jun27)─┘
Using buffer-size of 32
Connecting to /dev/ttyUSB0 (buffer-size 32)...
Trying to connect to REPL  connected
Testing if ubinascii.unhexlify exists ... Y
Retrieving root directories ... /boot.py/
Setting time ... Jun 27, 2020 20:46:47
Evaluating board_name ... pyboard
Retrieving time epoch ... Jan 01, 2000
Welcome to rshell. Use Control-D (or the exit command) to exit rshell.

/home/georgik/projects/esp32> cd /pyboard/
/pyboard> ls

7. January 2011

How to dump POST request with Python

Python contains one helpful module: SimpleHTTPServer. You can expose local directory via HTTP by the following command:

python -m SimpleHTTPServer

Python will start HTTP server at http://localhost:8000

It is very worthy when you’re doing some tests of web application.

The only problem is that SimpleHTTPServer does not support POST. Sometimes it’s very useful to see the content of POST request.

Is there any simple way how to achieve this in Python?

Here is a small extension of SimpleHTTPServer with do_POST handler:

import SimpleHTTPServer
import SocketServer
import logging
import cgi

PORT = 8000

class ServerHandler(SimpleHTTPServer.SimpleHTTPRequestHandler):

    def do_GET(self):

    def do_POST(self):
        form = cgi.FieldStorage(
        for item in form.list:

Handler = ServerHandler

httpd = SocketServer.TCPServer(("", PORT), Handler)

print "serving at port", PORT

You can download SimpleServer.py here and start it with command:

python SimpleServer.py

24. December 2009

Flash Game: Snowflakes – PF 2010

Collect all snowflakes. Click at the blue part of the screen to start the game.

Source code available in FXP format.

You can find more games at georgik.rocks/tag/games/