Contents: [Dobrica Pavlinušić's random unstructured stuff]
• Dobrica Pavlinušić's random unstructured stuff (jumper on pins) 
• Dobrica Pavlinušić's random unstructured stuff (I2C in userspace) 
• Dobrica Pavlinušić's random unstructured stuff (flashrom SPI) 
• Dobrica Pavlinušić's random unstructured stuff (linux kernel spi module) 
• Dobrica Pavlinušić's random unstructured stuff (linux kernel i2c module) 
• Dobrica Pavlinušić's random unstructured stuff (schematics and info) 
• Dobrica Pavlinušić's random unstructured stuff (alternative schematics) 

This is 5V device without modification! It works for me(tm) but you have been warned
http://www.eevblog.com/forum/repair/ch341a‑serial‑memory‑programmer‑power‑supply‑fix/ 
Just lift pin 28 and put some tape under it to prevent any short circuit. Then solder one wire from this pin to pin 2 of AMS1117 and also to C4. The side of the C4 to connect is the one connected to CH341A pin 9.
CHM341A‑3V3‑fix.jpg 

jumper on pins
1‑2 SPI flash programmer mode
 2‑3 TTL serial mode
supported out‑of‑box by flashrom, probably better option, but anyway:
https://github.com/setarcos/ch341prog 
dpavlin@nuc:/nuc/ch341a$ git clone https://github.com/setarcos/ch341prog
Cloning into 'ch341prog'...
remote: Counting objects: 104, done.
remote: Total 104 (delta 0), reused 0 (delta 0), pack-reused 104
Receiving objects: 100% (104/104), 34.79 KiB | 0 bytes/s, done.
Resolving deltas: 100% (61/61), done.
Checking connectivity... done.
dpavlin@nuc:/nuc/ch341a$ cd ch341prog/
dpavlin@nuc:/nuc/ch341a/ch341prog$ make
gcc -std=gnu99 -Wall ch341a.c main.c -o ch341prog  -lusb-1.0
dpavlin@nuc:/nuc/ch341a/ch341prog$ ./ch341prog 

Usage:
 -h, --help             display this message
 -i, --info             read the chip ID info
 -e, --erase            erase the entire chip
 -l, --length <bytes>   manually set length
 -w, --write <filename> write chip with data from filename
 -r, --read <filename>  read chip and save data to filename
 -t, --turbo            increase the i2c bus speed (-tt to use much faster speed)
 -d, --double           double the spi bus speed

I2C in userspace
https://sourceforge.net/projects/ch341eepromtool/ 
dpavlin@nuc:/nuc/ch341a/ch341eepromtool_0.5$ gcc -o ch341eeprom ch341eeprom.c ch341funcs.c -lusb-1.0
dpavlin@nuc:/nuc/ch341a/ch341eepromtool_0.5$ 
dpavlin@nuc:/nuc/ch341a/ch341eepromtool_0.5$ ./ch341eeprom 
ch341eeprom - an i2c EEPROM programming tool for the WCH CH341a IC
Version 0.5 copyright (c) 2011  asbokid <ballymunboy@gmail.com>

This program comes with asbolutely no warranty; This is free software,
and you are welcome to redistribute it under certain conditions:
GNU GPL v3 License: http://www.gnu.org/licenses/gpl.html

Usage:
 -h, --help             display this text
 -v, --verbose          verbose output
 -d, --debug            debug output
 -s, --size             size of EEPROM {24c32|24c64}
 -e, --erase            erase EEPROM (fill with 0xff)
 -w, --write <filename> write EEPROM with image from filename
 -r, --read  <filename> read EEPROM and save image to filename

Example:  ch341eeprom -v -s 24c64 -w bootrom.bin

flashrom SPI
Not needed anymore, included in mainline flashrom
git clone https://github.com/urjaman/flashrom/
git checkout -b origin/ch341a origin/ch341a

dpavlin@nuc:/nuc/flashrom$ sudo apt-get install pciutils-dev

linux kernel spi module
dpavlin@nuc:/nuc$ git clone https://github.com/gschorcht/spi-ch341-usb.git
Cloning into 'spi-ch341-usb'...
remote: Counting objects: 63, done.
remote: Total 63 (delta 0), reused 0 (delta 0), pack-reused 63
Unpacking objects: 100% (63/63), done.
dpavlin@nuc:/nuc$ cd spi-ch341-usb
dpavlin@nuc:/nuc/spi-ch341-usb$ make
make -C /usr/src/linux-headers-4.14.0-3-amd64/ M=/nuc/spi-ch341-usb  modules
make[1]: Entering directory '/usr/src/linux-headers-4.14.0-3-amd64'
  CC [M]  /nuc/spi-ch341-usb/spi-ch341-usb.o
  Building modules, stage 2.
  MODPOST 1 modules
  CC      /nuc/spi-ch341-usb/spi-ch341-usb.mod.o
  LD [M]  /nuc/spi-ch341-usb/spi-ch341-usb.ko
make[1]: Leaving directory '/usr/src/linux-headers-4.14.0-3-amd64'
dpavlin@nuc:/nuc/spi-ch341-usb$ 
dpavlin@nuc:/nuc/spi-ch341-usb$ sudo make install
[sudo] password for dpavlin: 

dpavlin@nuc:/nuc/spi-ch341-usb$ sudo modprobe spi-ch341-usb

[525021.048281] spi-ch341-usb 2-2.1.4:1.0: ch341_cfg_probe: output cs0 SPI slave with cs=0
[525021.048285] spi-ch341-usb 2-2.1.4:1.0: ch341_cfg_probe: output cs1 SPI slave with cs=1
[525021.048287] spi-ch341-usb 2-2.1.4:1.0: ch341_cfg_probe: output cs2 SPI slave with cs=2
[525021.048290] spi-ch341-usb 2-2.1.4:1.0: ch341_cfg_probe: input  gpio4 gpio=0 irq=0 (hwirq)
[525021.048292] spi-ch341-usb 2-2.1.4:1.0: ch341_cfg_probe: input  gpio5 gpio=1 irq=1 
[525021.048296] spi-ch341-usb 2-2.1.4:1.0: ch341_spi_probe: SPI master connected to SPI bus 0
[525021.048426] spi-ch341-usb 2-2.1.4:1.0: ch341_spi_probe: SPI device /dev/spidev0.0 created
[525021.048516] spi-ch341-usb 2-2.1.4:1.0: ch341_spi_probe: SPI device /dev/spidev0.1 created
[525021.048596] spi-ch341-usb 2-2.1.4:1.0: ch341_spi_probe: SPI device /dev/spidev0.2 created
[525021.049147] spi-ch341-usb 2-2.1.4:1.0: ch341_usb_probe: connected
[525021.049194] usbcore: registered new interface driver spi-ch341-usb

linux kernel i2c module
• https://github.com/gschorcht/i2c‑ch341‑usb 
root@nuc:/nuc# git clone https://github.com/gschorcht/i2c-ch341-usb.git
Cloning into 'i2c-ch341-usb'...
remote: Counting objects: 39, done.
remote: Total 39 (delta 0), reused 0 (delta 0), pack-reused 39
Unpacking objects: 100% (39/39), done.
root@nuc:/nuc# cd i2c-ch341-usb
root@nuc:/nuc/i2c-ch341-usb# make
make -C /usr/src/linux-headers-4.14.0-3-amd64/ M=/nuc/i2c-ch341-usb  modules
make[1]: Entering directory '/usr/src/linux-headers-4.14.0-3-amd64'
  CC [M]  /nuc/i2c-ch341-usb/i2c-ch341-usb.o
  Building modules, stage 2.
  MODPOST 1 modules
  CC      /nuc/i2c-ch341-usb/i2c-ch341-usb.mod.o
  LD [M]  /nuc/i2c-ch341-usb/i2c-ch341-usb.ko
make[1]: Leaving directory '/usr/src/linux-headers-4.14.0-3-amd64'
root@nuc:/nuc/i2c-ch341-usb# 
root@nuc:/nuc/i2c-ch341-usb# sudo make install

root@nuc:/nuc/i2c-ch341-usb# modprobe i2c-ch341-usb

[Wed Feb  7 16:37:00 2018] i2c-ch341-usb 2-2.1.4:1.0: ch341_cfg_probe: output gpio0 gpio=0 irq=0 
[Wed Feb  7 16:37:00 2018] i2c-ch341-usb 2-2.1.4:1.0: ch341_cfg_probe: output gpio1 gpio=1 irq=1 
[Wed Feb  7 16:37:00 2018] i2c-ch341-usb 2-2.1.4:1.0: ch341_cfg_probe: output gpio2 gpio=2 irq=2 
[Wed Feb  7 16:37:00 2018] i2c-ch341-usb 2-2.1.4:1.0: ch341_cfg_probe: output gpio3 gpio=3 irq=3 
[Wed Feb  7 16:37:00 2018] i2c-ch341-usb 2-2.1.4:1.0: ch341_cfg_probe: input  gpio4 gpio=4 irq=4 (hwirq)
[Wed Feb  7 16:37:00 2018] i2c-ch341-usb 2-2.1.4:1.0: ch341_cfg_probe: input  gpio5 gpio=5 irq=5 
[Wed Feb  7 16:37:00 2018] i2c-ch341-usb 2-2.1.4:1.0: ch341_cfg_probe: input  gpio6 gpio=6 irq=6 
[Wed Feb  7 16:37:00 2018] i2c-ch341-usb 2-2.1.4:1.0: ch341_cfg_probe: input  gpio7 gpio=7 irq=7 
[Wed Feb  7 16:37:00 2018] i2c-ch341-usb 2-2.1.4:1.0: ch341_i2c_probe: created i2c device /dev/i2c-8
[Wed Feb  7 16:37:00 2018] i2c-ch341-usb 2-2.1.4:1.0: ch341_i2c_set_speed: Change i2c bus speed to 100 kbps
[Wed Feb  7 16:37:00 2018] i2c-ch341-usb 2-2.1.4:1.0: ch341_usb_probe: connected
[Wed Feb  7 16:37:00 2018] usbcore: registered new interface driver i2c-ch341-usb

schematics and info
• http://onetransistor.blogspot.hr/2017/08/ch341a‑mini‑programmer‑schematic.html 
• http://www.zoobab.com/ch341‑usb‑spi‑i2c‑uart‑isp‑dongle 
I added soic 8 pinout over zif socket, because position of pin 1 is not obvious (or clearly marked anywhere on top). I suggest that you fix that with silver sharpy.

alternative schematics
https://github.com/Upcycle‑Electronics/CH341A‑Pro 
ch341Apro_schematicV01.pdf