Contents: [Dobrica Pavlinušić's random unstructured stuff]
• Dobrica Pavlinušić's random unstructured stuff (esptool and raspberry pi) 
• Dobrica Pavlinušić's random unstructured stuff (esp‑idf version) 
• Dobrica Pavlinušić's random unstructured stuff (v4.2.2) 
• Dobrica Pavlinušić's random unstructured stuff (v4.1.1 doesn't have ip_napt_enable) 
• Dobrica Pavlinušić's random unstructured stuff (enviroment) 
• Dobrica Pavlinušić's random unstructured stuff (IP_FORWARD enable in lwip) 
• Dobrica Pavlinušić's random unstructured stuff (build) 
• Dobrica Pavlinušić's random unstructured stuff (deploy to esp32 using esptool ttyUSB4) 
• Dobrica Pavlinušić's random unstructured stuff (serial) 
• Dobrica Pavlinušić's random unstructured stuff (webrepl) 
• Dobrica Pavlinušić's random unstructured stuff (ulx3s ppp) 

esptool and raspberry pi
I found out that older versions of esptool (like the ones deliveved by debian packages) don't work well on raspberry pi 2 and raspberry pi 4
root@pihdmi:/home/pi/linux-gpio-pinout# esptool -p /dev/ttyUSB0 read_mac
esptool.py v2.5.1
Serial port /dev/ttyUSB0
Connecting........_____....._____....._____....._____....._____....._____....._____

A fatal error occurred: Failed to connect to Espressif device: Timed out waiting for packet header

root@pihdmi:/home/pi/linux-gpio-pinout# /nuc/esp32/esptool/esptool.py --port /dev/ttyUSB0 read_mac
esptool.py v3.2-dev
Serial port /dev/ttyUSB0
Connecting........_____....._____.....___
Detecting chip type... ESP32
Chip is ESP32-D0WDQ6 (revision 1)
Features: WiFi, BT, Dual Core, 240MHz, VRef calibration in efuse, Coding Scheme None
Crystal is 40MHz
MAC: a4:cf:12:55:c5:60
Uploading stub...
Running stub...
Stub running...
MAC: a4:cf:12:55:c5:60
Hard resetting via RTS pin...

esp‑idf version
dpavlin@nuc:/nuc/esp32/esp-idf$ git remote -v
origin  https://github.com/espressif/esp-idf.git (fetch)
origin  https://github.com/espressif/esp-idf.git (push)

dpavlin@nuc:/nuc/esp32/esp-idf$ git checkout -b v3.3-upy 9e70825d1e1cbf7988cf36981774300066580ea7
dpavlin@nuc:/nuc/esp32/esp-idf$ git submodule update --init --recursive

For latest micropython v4.3 leaves too little memory available for esp32ecp/ecp5
v4.2.2
( 'gc', gc.isenabled(), 'alloc', gc.mem_alloc(), 'free', gc.mem_free() )
 gc True alloc 25632 free 85536
enough memory, but 50% packet loss for ping to remote ppp ip
v4.1.1 doesn't have ip_napt_enable
test alternative lwip lib
dpavlin@fpga:/esp32/esp-idf/components/lwip$ mv lwip lwip.old

dpavlin@fpga:/esp32/esp-idf/components/lwip$ git clone https://github.com/martin-ger/esp-lwip lwip
Cloning into 'lwip'...
remote: Enumerating objects: 49642, done.
remote: Total 49642 (delta 0), reused 0 (delta 0), pack-reused 49642
Receiving objects: 100% (49642/49642), 9.70 MiB | 14.52 MiB/s, done.
Resolving deltas: 100% (37485/37485), done.

it does work, but slowly:
dpavlin@nuc:/tmp/esp-lwip$ iperf3 -c 10.0.5.2
Connecting to host 10.0.5.2, port 5201
[  5] local 192.168.3.40 port 52086 connected to 10.0.5.2 port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec   102 KBytes   833 Kbits/sec    1   28.3 KBytes
[  5]   1.00-2.00   sec  0.00 Bytes  0.00 bits/sec   10   14.1 KBytes
[  5]   2.00-3.00   sec  82.0 KBytes   673 Kbits/sec    2   22.6 KBytes
[  5]   3.00-4.00   sec  0.00 Bytes  0.00 bits/sec    0   28.3 KBytes
[  5]   4.00-5.00   sec  0.00 Bytes  0.00 bits/sec    4   19.8 KBytes
[  5]   5.00-6.00   sec  93.3 KBytes   765 Kbits/sec    4   18.4 KBytes
[  5]   6.00-7.00   sec  0.00 Bytes  0.00 bits/sec    3   5.66 KBytes
[  5]   7.00-8.00   sec  0.00 Bytes  0.00 bits/sec    0   15.6 KBytes
[  5]   8.00-9.00   sec  63.6 KBytes   522 Kbits/sec    0   15.6 KBytes
[  5]   9.00-10.00  sec  0.00 Bytes  0.00 bits/sec    2   5.66 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec   341 KBytes   279 Kbits/sec   26             sender
[  5]   0.00-10.18  sec   216 KBytes   174 Kbits/sec                  receiver

enviroment
dpavlin@nuc:/nuc/upy/micropython/ports/esp32$ cat env.sh
export PATH=/nuc/esp32/xtensa-esp32-elf/bin/:$PATH
export ESPIDF=/nuc/esp32/esp-idf/

IP_FORWARD enable in lwip
dpavlin@nuc:/nuc/upy/micropython/ports/esp32$ git diff
diff --git a/ports/esp32/Makefile b/ports/esp32/Makefile
index 756bc8f89..aa03a6370 100644
--- a/ports/esp32/Makefile
+++ b/ports/esp32/Makefile
@@ -494,7 +494,7 @@ ESPIDF_SPI_FLASH_O = $(patsubst %.c,%.o,$(wildcard $(ESPCOMP)/spi_flash/*.c))

 ESPIDF_ULP_O = $(patsubst %.c,%.o,$(wildcard $(ESPCOMP)/ulp/*.c))

-$(BUILD)/$(ESPCOMP)/lwip/%.o: CFLAGS += -Wno-address -Wno-unused-variable -Wno-unused-but-set-variable
+$(BUILD)/$(ESPCOMP)/lwip/%.o: CFLAGS += -Wno-address -Wno-unused-variable -Wno-unused-but-set-variable -DIP_FORWARD=1
 ESPIDF_LWIP_O = $(patsubst %.c,%.o,\
        $(wildcard $(ESPCOMP)/lwip/apps/dhcpserver/*.c) \
        $(wildcard $(ESPCOMP)/lwip/lwip/src/api/*.c) \

build
dpavlin@nuc:/nuc/upy/micropython/ports/esp32$ make V=1

...

xtensa-esp32-elf-size build-GENERIC/application.elf
   text    data     bss     dec     hex filename
1100148  275360   37372 1412880  158f10 build-GENERIC/application.elf
Create build-GENERIC/application.bin
/nuc/esp32/esp-idf//components/esptool_py/esptool/esptool.py --chip esp32 elf2image --flash_mode dio --flash_freq 40m --flash_size 4MB build-GENERIC/application.elf
esptool.py v2.8
Create build-GENERIC/firmware.bin
python3 makeimg.py build-GENERIC/bootloader.bin build-GENERIC/partitions.bin build-GENERIC/application.bin build-GENERIC/firmware.bin
bootloader     21360
partitions      3072
application  1375648
total        1441184

deploy to esp32 using esptool ttyUSB4
dpavlin@nuc:/nuc/upy/micropython/ports/esp32$ make V=1 PORT=/dev/ttyUSB4  deploy
Building with ESP IDF v3
python3 ../../py/makeversionhdr.py build-GENERIC/genhdr/mpversion.h
python3 ../../tools/makemanifest.py -o build-GENERIC/frozen_content.c -v "MPY_DIR=../.." -v "MPY_LIB_DIR=../../../micropython-lib" -v "PORT_DIR=/nuc/upy/micropython/ports/esp32" -v "BOARD_DIR=boards/GENERIC" -b "build-GENERIC" -f"-march=xtensawin" boards/manifest.py
Writing build-GENERIC/firmware.bin to the board
/nuc/esp32/esp-idf//components/esptool_py/esptool/esptool.py --chip esp32 --port /dev/ttyUSB4 --baud 460800 write_flash -z --flash_mode dio --flash_freq 40m 0x1000 build-GENERIC/firmware.bin
esptool.py v2.8
Serial port /dev/ttyUSB4
Connecting........_____....._____....._____...
Chip is ESP32D0WDQ6 (revision 1)
Features: WiFi, BT, Dual Core, 240MHz, VRef calibration in efuse, Coding Scheme None
Crystal is 40MHz
MAC: 24:0a:c4:31:d6:38
Uploading stub...
Running stub...
Stub running...
Changing baud rate to 460800
Changed.
Configuring flash size...
Auto-detected Flash size: 4MB
Compressed 1437088 bytes to 921637...
Wrote 1437088 bytes (921637 compressed) at 0x00001000 in 21.5 seconds (effective 535.8 kbit/s)...
Hash of data verified.

Leaving...
Hard resetting via RTS pin...

serial
dpavlin@nuc:/nuc/upy/micropython/ports/esp32$ microcom -p /dev/ttyUSB4
connected to /dev/ttyUSB4
Escape character: Ctrl-\
Type the escape character to get to the prompt.

>>>
MPY: soft reboot
AP config:  ('192.168.4.1', '255.255.255.0', '192.168.4.1', '0.0.0.0')
network config: ('192.168.3.208', '255.255.255.0', '192.168.3.1', '192.168.3.1')
FTP server started on 192.168.4.1:21
FTP server started on 192.168.3.208:21
 esp32 mac: 24:0a:c4:31:d6:38 esp32upy
MicroPython v1.14-dirty on 2021-07-25; ESP32 module with ESP32
Type "help()" for more information.
>>> import machine
>>> machine.reset()
ets Jun  8 2016 00:22:57

rst:0xc (SW_CPU_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:2
load:0x3fff0018,len:4
load:0x3fff001c,len:4972
load:0x40078000,len:10600
load:0x40080400,len:5684
entry 0x400806bc
AP config:  ('192.168.4.1', '255.255.255.0', '192.168.4.1', '0.0.0.0')
network config: ('192.168.3.208', '255.255.255.0', '192.168.3.1', '192.168.3.1')
FTP server started on 192.168.4.1:21
FTP server started on 192.168.3.208:21
 esp32 mac: 24:0a:c4:31:d6:38 esp32upy
MicroPython v1.14-dirty on 2021-07-25; ESP32 module with ESP32
Type "help()" for more information.

webrepl
• https://github.com/Hermann‑SW/webrepl/blob/master/webrepl_client.py  ‑‑ provide python repl without using usb serial port
• https://github.com/kost/webrepl‑python 
ulx3s  ppp
• https://github.com/emard/esp32ppp 
• https://github.com/micropython/micropython/issues/5369