Information wants to be free...

Reverse SSH Tunnel Listener

The Reverse SSH Tunnel Launcher script I posted a while ago has some limitations. The worst part is that the tunnel is only open for 5 minutes, leaving too little time to get any work done. This is kind of by design, to prevent having these connections open and "live" when not in use.

The solution to this limitation is another small script, this time just hacked together as a Bourne shell script. Take a look:


while /bin/true; do
  if /bin/netstat -tln | fgrep > /dev/null; then
    ssh localhost -p 1337 screen -d -m ssh -v -R 1338:localhost:22 -N -p 22
    echo "New tunnel established!"
  sleep 10

This script will loop forever and wait for a socket to appear on the port (1337) opened by the original launcher. Once this happens, a new tunnel is created (on port 1338) in parallel which will persist forever through a screen session.

Topic: Scripts and Code, by Kjetil @ 02/02-2020, Article Link


This is a game project I have had lying around for many years, which I finally made into something usable. The initial idea was to make a side-scroller using the SDL library, and the project codename was "Strawman", so that just became the title as well.

The end result is a highly configurable yet simple game. The map data is stored in a text file and can be easily changed. The "game engine" itself is configured through a bunch of #define macros.

Here's a screenshot:

Strawman screenshot

And the corresponding part of the map data, rotated by 90 degrees on purpose, so adding more lines makes the map longer horizontally:

# P
###  #  CCC
###  #E CCC
###  #  CCC

        # CC
#       # CC
##      # CC

The source code is released under the MIT license and can be downloaded here.

Topic: Open Source, by Kjetil @ 01/01-2020, Article Link

Commodore PC 30-III Repair

The Commodore PC 30-III is a AT-class 286 clone PC running at 12MHz with 1MB of RAM. My first and initial problem was the battery failure upon booting:

Commodore PC 30-III Battery Failure

For some reason, It was not possible to get past this error and continue booting anyway, so a replacement was needed. I got hold of a Glitch Works GW-12887-1 which can replace the original Dallas 1287 RTC in this machine:

Commodore PC 30-III Dallas DS1287 RTC

This is unfortunately soldered directly to the motherboard. But I cut a socket and soldered that one on instead:

Commodore PC 30-III U201 Socket Replacement

In which the replacement fits nicely:

Commodore PC 30-III GW-12887-1

This got the machine booting properly. But after a while of playing around with Compact Flash disk replacements, magic smoke suddenly appeared. Which became my second problem. I located the source; a burned ceramic capacitor:

Commodore PC 30-III Burned Ceramic Capacitor

From what I could find out online, these capacitors can fail if cracks appear in them, and moisture gets in over time. So that's most likely what happened to this 30 year old component. I got a replacement and removed the bad one, which disintegrated almost by itself:

Commodore PC 30-III Capacitor Replacement

The brand new ceramic capacitor in place:

Commodore PC 30-III New Capacitor

The machine is now up and running again:

Commodore PC 30-III Front

Topic: Repair, by Kjetil @ 08/12-2019, Article Link

Linux Distribution for 386SX

I have a Commodore PC 50-II system with a Intel 386SX CPU running at 16MHz and only 5MB of RAM, in addition, the harddrive controller and harddrive is also missing. To get around this, I have installed a 3Com 3C509B-TPO ISA Network card and have managed to boot Linux on this ancient PC over the network instead.

At first I tried to use Buildroot, but I had to give up on this in the end, as it seems that pure 386 is not supported anywhere anymore. So instead, I have gone the route of building everything from scratch, so I could pick and choose specific source versions of GCC and the Linux kernel that supports 386 with math emulation. The end result is a cross-compiling toolchain for i386, a stripped down kernel and Busybox-based rootfs mounted over NFS from another host computer.

I ended up using these specific software versions:
* linux-
* gcc-3.4.6
* busybox-1.01
* uClibc-
* binutils-2.32

I also had to statically link everything. I tried with dynamic linking in the beginning but the system would hang during boot, and I didn't want to troubleshoot this any further.

I have made some scripts to greatly simplify the whole process of building the cross-compiling toolchain and all the binaries. Bundled in a file here.

Unpack this into a directory and then simply run the following:


I have used these on a Slackware 14.2 box with GCC 5.3.0
The result will be a directory with the "rootfs" and a "bzImage" located inside the kernel build tree.

The rootfs is exported over NFS in /etc/exports like this:

/home/nfs/rootfs *(rw,sync,no_root_squash,no_all_squash,no_subtree_check)

Also note that the legacy NFSv2 protocol needs to be actived!

To prepare the kernel is the tricky part. To load it over TFTP with Etherboot you have to use the mkelf-linux script from the mknbi package. This package is not compilable on modern Linux distributions, so I ended up compiling and using it from an old Slackware 11.0 installation running in a QEMU virtual machine.

I used the command as follows:

mkelf-linux --output=pc50linux.nb --ip="" --append="root=/dev/nfs nfsroot=/home/nfs/rootfs" bzImage

Where .3 is the booted client PC, .2 is the NFS server and .1 is the gateway and TFTP server.

The final step is to activate the TFTP/DHCP server. I used dnsmasq for this, with the following relevant configuration:


Some additional information: I have no Boot ROM on the Ethernet card, so I used a floppy disk to actually kick-start the network booting. More specifically, the "3c509.dsk" image made from compiling parts of the "Etherboot" package. Since this also isn't compilable on modern distributions, I had to use the Slackware 11.0 QEMU virtual machine again.

Commodore PC 50-II

Topic: Configuration, by Kjetil @ 01/12-2019, Article Link

ADCQ1706 USB Oscilloscope

On a trip to Japan I bought one of these strange USB oscilloscopes. It seems it was designed for use with a Raspberry Pi, but I wanted to use it on a regular Linux desktop PC. Fortunately, the available "client" software for the RPi is written in Python, but it has several limitations. It's all in Japanese and it looks to be based around a web-server capturing still images. However, due to source code availability, I could easily create a new client.

What I present here is a Python PyGame-based solution instead, which has a graphical screen that updates in real time:


I have uploaded the code to GitLab and GitHub, but it's also presented here:

import serial
import pygame
import time

class Oscilloscope(object):
    def __init__(self, tty_dev='/dev/ttyUSB0', trig_level=2048):
        self._con = serial.Serial(tty_dev, 115200, timeout=2.0)
        self._settings = {
            1 : {'hsync' : 3, 'trig' : trig_level, 'rise' : 1},
            2 : {'hsync' : 3, 'trig' : trig_level, 'rise' : 1}}

    def get_samples(self, channel):
        hsync = str(self._settings[channel]['hsync'])
        trig  = str(self._settings[channel]['trig'])
        rise  = str(self._settings[channel]['rise'])

        self._con.write('ST' + hsync + str(channel) + trig + rise + 'E')
        data =
        if len(data) != 4003:
            return None
        if not (data[0] == 'S') and (data[1] == 'M') and (data[4002] == 'E'):
            return None

        samples = list()
        for i in range(0, 2000):
            samples.append(int((ord(data[i*2+2]) & 0x7F) + (ord(data[i*2+3]) & 0x1F) * 128))
        return samples

    def increase_hsync(self, channel):
        if self._settings[channel]['hsync'] < 6:
            self._settings[channel]['hsync'] += 1

    def decrease_hsync(self, channel):
        if self._settings[channel]['hsync'] > 0:
            self._settings[channel]['hsync'] -= 1

    def get_hsync(self, channel):
        return self._settings[channel]['hsync']

    def toggle_trig_rise(self, channel):
        if self._settings[channel]['rise'] == 1:
            self._settings[channel]['rise'] = 0
            self._settings[channel]['rise'] = 1

    def increase_trig_level(self, channel):
        if self._settings[channel]['trig'] < 3968:
            self._settings[channel]['trig'] += 256

    def decrease_trig_level(self, channel):
        if self._settings[channel]['trig'] > 128:
            self._settings[channel]['trig'] -= 256

    def get_trig_level(self, channel):
        return self._settings[channel]['trig']

class GUI(object):
    def __init__(self, oscilloscope, scale=1):
        if scale not in [1,2,4]:
            raise Exception("Invalid scale")
        self._scale = scale
        self._osc = oscilloscope
        self._ch_active = {1 : True, 2 : True}
        self._screen = pygame.display.set_mode((500 * scale, 512 * scale))
        self._font = pygame.font.Font(pygame.font.get_default_font(), 12 * scale)

    def _toggle_channel(self, channel):
        if self._ch_active[channel] == True:
            self._ch_active[channel] = False
            self._ch_active[channel] = True 

    def _draw_samples(self, samples, color):
        prev_y = None
        for sample_no, sample in enumerate(samples):
            y = (4096 - sample) / (8 / self._scale)
            x = sample_no / (4 / self._scale)
            if prev_y == None:
                prev_y = y
            pygame.draw.line(self._screen, color, (x, prev_y), (x, y))
            prev_y = y
    def _draw_volt_grid(self):
        for pos, volt in [(48,1.5), (715,1), (1381,0.5), (2048,0), (2715,-0.5), (3381,-1), (4048,-1.5)]:
            y = pos / (8 / self._scale)
            pygame.draw.line(self._screen, (128, 128, 128), (0, y), ((500 * self._scale), y))
            text = self._font.render(str(volt) + "V", True, (128, 128, 128))
            if text.get_height() > y:
                self._screen.blit(text, (0, y + (1 * self._scale)))
                self._screen.blit(text, (0, y - text.get_height() + (1 * self._scale)))

    def _draw_time_grid(self, channel, color):
        hsync = self._osc.get_hsync(channel)
        if hsync == 0:
            time = [0,5,10,15,20,25,30,35,40,45]
            unit = "us"
        elif hsync == 1:
            time = [0,10,20,30,40,50,60,70,80,90]
            unit = "us"
        elif hsync == 2:
            time = [0,50,100,150,200,250,300,350,400,450]
            unit = "us"
        elif hsync == 3:
            time = [0,100,200,300,400,500,600,700,800,900]
            unit = "us"
        elif hsync == 4:
            time = [0,1,2,3,4,5,6,7,8,9]
            unit = "ms"
        elif hsync == 5:
            time = [0,2,4,6,8,10,12,14,16,18]
            unit = "ms"
        elif hsync == 6:
            time = [0,10,20,30,40,50,60,70,80,90]
            unit = "ms"

        for index in range(0, 10):
            x = index * (50 * self._scale)
            if x > 0:
                pygame.draw.line(self._screen, (128, 128, 128), (x, 0), (x, (512 * self._scale)))
            text = self._font.render(str(time[index]) + unit, True, color)
            if channel == 1:
                self._screen.blit(text, (x + (1 * self._scale), 0))
            if channel == 2:
                self._screen.blit(text, (x + (1 * self._scale), (512 * self._scale) - text.get_height()))

    def _draw_trig_line(self, channel, color):
        y = (4096 - self._osc.get_trig_level(channel)) / (8 / self._scale)
        pygame.draw.line(self._screen, color, (0, y), ((500 * self._scale), y))

    def loop(self):
        while True:
            for event in pygame.event.get():
                if event.type == pygame.QUIT:
                elif event.type == pygame.KEYDOWN:
                    if event.key == pygame.K_ESCAPE or event.key == pygame.K_q:
                    elif event.key == pygame.K_s:
              , "oscilloscope.png")
                        print "Screenshot saved to 'oscilloscope.png'."
                    elif event.key == pygame.K_1:
                    elif event.key == pygame.K_2:
                    elif event.key == pygame.K_3:
                    elif event.key == pygame.K_4:
                    elif event.key == pygame.K_5:
                    elif event.key == pygame.K_6:
                    elif event.key == pygame.K_7:
                    elif event.key == pygame.K_8:
                    elif event.key == pygame.K_e:
                    elif event.key == pygame.K_r:
                    elif event.key == pygame.K_t:
                    elif event.key == pygame.K_y:


            if self._ch_active[1]:
                self._draw_time_grid(1, (255,128,128))
                self._draw_trig_line(1, (255,128,128))
                samples = self._osc.get_samples(1)
                self._draw_samples(samples, (255,0,0))

            if self._ch_active[2]:
                self._draw_time_grid(2, (128,128,255))
                self._draw_trig_line(2, (128,128,255))
                samples = self._osc.get_samples(2)
                self._draw_samples(samples, (0,0,255))

            if (not self._ch_active[1]) and (not self._ch_active[2]):
                time.sleep(0.1) # To avoid 100% CPU usage.


if __name__ == "__main__":
    import sys
    import getopt

    def print_usage_and_exit():
        print "Usage: %s [options]" % (sys.argv[0])
        print "Options:"
        print "  -h         Display this help and exit."
        print "  -d DEV     Serial TTY DEV to use instead of /dev/ttyUSB0."
        print "  -s SCALE   Scale of GUI, value 1, 2 or 4."
        print " "

    def print_keys():
        print "Keys:"
        print "  1 = Toggle channel #1"
        print "  2 = Toggle channel #2"
        print "  3 = Increase time/div for channel #1"
        print "  4 = Decrease time/div for channel #1"
        print "  5 = Increase time/div for channel #2"
        print "  6 = Decrease time/div for channel #2"
        print "  7 = Toggle rise/fall trigging for channel #1"
        print "  8 = Toggle rise/fall trigging for channel #2"
        print "  E = Increase trig level for channel #1"
        print "  R = Decrease trig level for channel #1"
        print "  T = Increase trig level for channel #2"
        print "  Y = Decrease trig level for channel #2"
        print "  S = Screenshot"
        print "  Q = Quit"

        opts, args = getopt.getopt(sys.argv[1:], "hd:s:")
    except getopt.GetoptError as err:
        print "Error:", str(err)

    tty_dev = None
    scale = None
    for o, a in opts:
        if o == '-h':
        elif o == '-d':
            tty_dev = a
        elif o == '-s':
            scale = int(a)

    if tty_dev:
        osc = Oscilloscope(tty_dev)
        osc = Oscilloscope()

    if scale:
        gui = GUI(osc, scale)
        gui = GUI(osc)


Topic: Scripts and Code, by Kjetil @ 01/11-2019, Article Link

Commodore 1541-II Floppy Drive Repair

I was able to repair my Commodore 1541-II floppy drive, which is typically used together with the Commodore 64.

The first problem was that I do not have the original (external) power supply, but fortunately it uses fairly standard +5V and +12V voltages, which are also used by most PC hardware. So I made an adapter from a 4-pin molex to a 4-pin DIN connector:

Commodore 1541-II Power Adapter

The pinout of the DIN connector can be found here among other places.

When powering up the drive for the first time, it would keep the drive motor running constantly, which is apparently a known problem. Some other people online said this could be caused by a faulty PSU or bad ROM chip...

When I attempted to continue troubleshooting the next day, the situation had worsened. Now the power LED on the drive would flash a little on power on and slowly fade away. Symptoms of a short circuit or something perhaps...

With no idea on what to do about this, I decided to try to replace the electrolytic capacitors, which people often do on restoration/repair projects.

There are only three of them on the main board, all 10uF and 25V, located here:

Commodore 1541-II Capacitor Locations

Old and new replacements:

Commodore 1541-II Capacitor Replacement

To my surprise, this actually worked, and the drive is now working:

Commodore 1541-II Working

I have a theory: Two of those capacitors I changed are between the incoming 12V/5V and ground, acting as "decouping/bypass" to filter out noise. If there happened to be a short circuit or weakened resistance in the capacitors, that would explain parts of the symptoms at least.

Topic: Repair, by Kjetil @ 26/10-2019, Article Link

SSD1306 Wi-Fi Status

Here is another use of the SSD1306 miniature OLED display. Instead of loading an image like my previous project, this code contains character data and can display text. I have combined this with some simple hacks to retrieve and display Wi-Fi status information from the host. This is also meant to be connected to a Raspberry Pi 3.

Take a look:

import smbus
import subprocess
import re
import time

chardata = dict()
chardata['@'] = "\x3c\x66\x6e\x6e\x60\x62\x3c\x00"
chardata['A'] = "\x18\x3c\x66\x7e\x66\x66\x66\x00"
chardata['B'] = "\x7c\x66\x66\x7c\x66\x66\x7c\x00"
chardata['C'] = "\x3c\x66\x60\x60\x60\x66\x3c\x00"
chardata['D'] = "\x78\x6c\x66\x66\x66\x6c\x78\x00"
chardata['E'] = "\x7e\x60\x60\x78\x60\x60\x7e\x00"
chardata['F'] = "\x7e\x60\x60\x78\x60\x60\x60\x00"
chardata['G'] = "\x3c\x66\x60\x6e\x66\x66\x3c\x00"
chardata['H'] = "\x66\x66\x66\x7e\x66\x66\x66\x00"
chardata['I'] = "\x3c\x18\x18\x18\x18\x18\x3c\x00"
chardata['J'] = "\x1e\x0c\x0c\x0c\x0c\x6c\x38\x00"
chardata['K'] = "\x66\x6c\x78\x70\x78\x6c\x66\x00"
chardata['L'] = "\x60\x60\x60\x60\x60\x60\x7e\x00"
chardata['M'] = "\x63\x77\x7f\x6b\x63\x63\x63\x00"
chardata['N'] = "\x66\x76\x7e\x7e\x6e\x66\x66\x00"
chardata['O'] = "\x3c\x66\x66\x66\x66\x66\x3c\x00"
chardata['P'] = "\x7c\x66\x66\x7c\x60\x60\x60\x00"
chardata['Q'] = "\x3c\x66\x66\x66\x66\x3c\x0e\x00"
chardata['R'] = "\x7c\x66\x66\x7c\x78\x6c\x66\x00"
chardata['S'] = "\x3c\x66\x60\x3c\x06\x66\x3c\x00"
chardata['T'] = "\x7e\x18\x18\x18\x18\x18\x18\x00"
chardata['U'] = "\x66\x66\x66\x66\x66\x66\x3c\x00"
chardata['V'] = "\x66\x66\x66\x66\x66\x3c\x18\x00"
chardata['W'] = "\x63\x63\x63\x6b\x7f\x77\x63\x00"
chardata['X'] = "\x66\x66\x3c\x18\x3c\x66\x66\x00"
chardata['Y'] = "\x66\x66\x66\x3c\x18\x18\x18\x00"
chardata['Z'] = "\x7e\x06\x0c\x18\x30\x60\x7e\x00"
chardata['['] = "\x3c\x30\x30\x30\x30\x30\x3c\x00"
chardata[']'] = "\x3c\x0c\x0c\x0c\x0c\x0c\x3c\x00"
chardata[' '] = "\x00\x00\x00\x00\x00\x00\x00\x00"
chardata['!'] = "\x18\x18\x18\x18\x00\x00\x18\x00"
chardata['"'] = "\x66\x66\x66\x00\x00\x00\x00\x00"
chardata['#'] = "\x66\x66\xff\x66\xff\x66\x66\x00"
chardata['$'] = "\x18\x3e\x60\x3c\x06\x7c\x18\x00"
chardata['%'] = "\x62\x66\x0c\x18\x30\x66\x46\x00"
chardata['&'] = "\x3c\x66\x3c\x38\x67\x66\x3f\x00"
chardata['\''] = "\x06\x0c\x18\x00\x00\x00\x00\x00"
chardata['('] = "\x0c\x18\x30\x30\x30\x18\x0c\x00"
chardata[')'] = "\x30\x18\x0c\x0c\x0c\x18\x30\x00"
chardata['*'] = "\x00\x66\x3c\xff\x3c\x66\x00\x00"
chardata['+'] = "\x00\x18\x18\x7e\x18\x18\x00\x00"
chardata[','] = "\x00\x00\x00\x00\x00\x18\x18\x30"
chardata['-'] = "\x00\x00\x00\x7e\x00\x00\x00\x00"
chardata['.'] = "\x00\x00\x00\x00\x00\x18\x18\x00"
chardata['/'] = "\x00\x03\x06\x0c\x18\x30\x60\x00"
chardata['0'] = "\x3c\x66\x6e\x76\x66\x66\x3c\x00"
chardata['1'] = "\x18\x18\x38\x18\x18\x18\x7e\x00"
chardata['2'] = "\x3c\x66\x06\x0c\x30\x60\x7e\x00"
chardata['3'] = "\x3c\x66\x06\x1c\x06\x66\x3c\x00"
chardata['4'] = "\x06\x0e\x1e\x66\x7f\x06\x06\x00"
chardata['5'] = "\x7e\x60\x7c\x06\x06\x66\x3c\x00"
chardata['6'] = "\x3c\x66\x60\x7c\x66\x66\x3c\x00"
chardata['7'] = "\x7e\x66\x0c\x18\x18\x18\x18\x00"
chardata['8'] = "\x3c\x66\x66\x3c\x66\x66\x3c\x00"
chardata['9'] = "\x3c\x66\x66\x3e\x06\x66\x3c\x00"
chardata[':'] = "\x00\x00\x18\x00\x00\x18\x00\x00"
chardata[';'] = "\x00\x00\x18\x00\x00\x18\x18\x30"
chardata['<'] = "\x0e\x18\x30\x60\x30\x18\x0e\x00"
chardata['='] = "\x00\x00\x7e\x00\x7e\x00\x00\x00"
chardata['>'] = "\x70\x18\x0c\x06\x0c\x18\x70\x00"
chardata['?'] = "\x3c\x66\x06\x0c\x18\x00\x18\x00"
chardata['a'] = "\x00\x00\x3c\x06\x3e\x66\x3e\x00"
chardata['b'] = "\x00\x60\x60\x7c\x66\x66\x7c\x00"
chardata['c'] = "\x00\x00\x3c\x60\x60\x60\x3c\x00"
chardata['d'] = "\x00\x06\x06\x3e\x66\x66\x3e\x00"
chardata['e'] = "\x00\x00\x3c\x66\x7e\x60\x3c\x00"
chardata['f'] = "\x00\x0e\x18\x3e\x18\x18\x18\x00"
chardata['g'] = "\x00\x00\x3e\x66\x66\x3e\x06\x7c"
chardata['h'] = "\x00\x60\x60\x7c\x66\x66\x66\x00"
chardata['i'] = "\x00\x18\x00\x38\x18\x18\x3c\x00"
chardata['j'] = "\x00\x06\x00\x06\x06\x06\x06\x3c"
chardata['k'] = "\x00\x60\x60\x6c\x78\x6c\x66\x00"
chardata['l'] = "\x00\x38\x18\x18\x18\x18\x3c\x00"
chardata['m'] = "\x00\x00\x66\x7f\x7f\x6b\x63\x00"
chardata['n'] = "\x00\x00\x7c\x66\x66\x66\x66\x00"
chardata['o'] = "\x00\x00\x3c\x66\x66\x66\x3c\x00"
chardata['p'] = "\x00\x00\x7c\x66\x66\x7c\x60\x60"
chardata['q'] = "\x00\x00\x3e\x66\x66\x3e\x06\x06"
chardata['r'] = "\x00\x00\x7c\x66\x60\x60\x60\x00"
chardata['s'] = "\x00\x00\x3e\x60\x3c\x06\x7c\x00"
chardata['t'] = "\x00\x18\x7e\x18\x18\x18\x0e\x00"
chardata['u'] = "\x00\x00\x66\x66\x66\x66\x3e\x00"
chardata['v'] = "\x00\x00\x66\x66\x66\x3c\x18\x00"
chardata['w'] = "\x00\x00\x63\x6b\x7f\x3e\x36\x00"
chardata['x'] = "\x00\x00\x66\x3c\x18\x3c\x66\x00"
chardata['y'] = "\x00\x00\x66\x66\x66\x3e\x0c\x78"
chardata['z'] = "\x00\x00\x7e\x0c\x18\x30\x7e\x00"

class SSD1306(object):
    def __init__(self, bus=1, address=0x3c):
        self._address = address
        self._bus = smbus.SMBus(bus)

        self._command(0xae) # Display off.

        self._command(0xa8) # Multiplex ratio...
        self._command(0x3f) # ...63
        self._command(0xd3) # Display offset...
        self._command(0x00) # ...0
        self._command(0x40) # Display start line at 0.
        self._command(0xa1) # Segment Re-map with column 127 mapped to SEG0.
        self._command(0xc8) # Remapped mode, scan from COM[N-1] to COM0.
        self._command(0xda) # COM pins hardware configuration...
        self._command(0x32) # ...Alternative and Left/Right
        self._command(0xa4) # Entire display ON.
        self._command(0xa6) # Inverse display mode.
        self._command(0xd5) # Display clock...
        self._command(0x80) # ...No clock divide ratio and max frequency.
        self._command(0x8d) # Charge pump...
        self._command(0x14) # ...Enabled.
        self._command(0x20) # Memory addressing mode...
        self._command(0x20) # ...Horizontal.

        self._command(0xaf) # Display on.
    def _command(self, command_byte):
        self._bus.write_byte_data(self._address, 0x00, command_byte)

    def _data(self, data_byte):
        self._bus.write_byte_data(self._address, 0x40, data_byte)

    def reset_cursor(self):
        self._command(0x21) # Column address...
        self._command(0x00) # ...start at 0...
        self._command(0x7f) # ...end at 127.
        self._command(0x22) # Page address...
        self._command(0x00) # ...start at 0...
        self._command(0x07) # ...end at 7.

    def putc(self, char):
        if char in chardata:
            for column in range(0, 8):
                byte  = ((ord(chardata[char][0]) >> (7 - column)) & 1) << 1
                byte += ((ord(chardata[char][1]) >> (7 - column)) & 1) << 0
                byte += ((ord(chardata[char][2]) >> (7 - column)) & 1) << 3
                byte += ((ord(chardata[char][3]) >> (7 - column)) & 1) << 2
                byte += ((ord(chardata[char][4]) >> (7 - column)) & 1) << 5
                byte += ((ord(chardata[char][5]) >> (7 - column)) & 1) << 4
                byte += ((ord(chardata[char][6]) >> (7 - column)) & 1) << 7
                byte += ((ord(chardata[char][7]) >> (7 - column)) & 1) << 6

    def puts(self, string):
        for char in string:

class WiFiStatus(object):
    def __init__(self, interface):
        self._interface = interface

    def _get_status(self):
        iwconfig = subprocess.check_output("iwconfig %s" % (self._interface), shell=True)
        ifconfig = subprocess.check_output("ifconfig %s" % (self._interface), shell=True)

        match ='inet ([^\ ]+?) ', ifconfig, flags=re.MULTILINE)
        if match:
            inet_address =
            inet_address = ""

        match ='RX packets ([^\ ]+?) ', ifconfig, flags=re.MULTILINE)
        if match:
            rx_packets =
            rx_packets = ""

        match ='TX packets ([^\ ]+?) ', ifconfig, flags=re.MULTILINE)
        if match:
            tx_packets =
            tx_packets = ""

        match ='ESSID:"([^"]+?)"', iwconfig, flags=re.MULTILINE)
        if match:
            essid =
            essid = ""

        match ='Link Quality=(\d+/\d+)', iwconfig, flags=re.MULTILINE)
        if match:
            link_quality =
            link_quality = ""

        match ='Signal level=(-\d+ dBm)', iwconfig, flags=re.MULTILINE)
        if match:
            signal_level =
            signal_level = ""

        match ='Bit Rate=([\.\d]+ Mb/s)', iwconfig, flags=re.MULTILINE)
        if match:
            bit_rate =
            bit_rate = ""

        match ='Tx-Power=(\d+ dBm)', iwconfig, flags=re.MULTILINE)
        if match:
            tx_power =
            tx_power = ""

        return (inet_address, rx_packets, tx_packets, essid, link_quality, signal_level, bit_rate, tx_power)

    def loop(self):
        display = SSD1306()

        while True:
            (ia, rx, tx, si, lq, sl, br, tp) = self._get_status()
            display.puts((si + "                ")[:16])
            display.puts((ia + "                ")[:16])
            display.puts(("Link: " + lq + "          ")[:16])
            display.puts(("Sig: " + sl + "           ")[:16])
            display.puts(("Rate: " + br + "          ")[:16])
            display.puts(("Pow: " + tp + "           ")[:16])
            display.puts(("Rx: " + rx + "            ")[:16])
            display.puts(("Tx: " + tx + "            ")[:16])

if __name__ == "__main__":
    import sys

    if len(sys.argv) < 2:
        print "Usage: %s <interface>" % (sys.argv[0])

    ws = WiFiStatus(sys.argv[1])

Topic: Scripts and Code, by Kjetil @ 05/10-2019, Article Link

RSS Feed

Moving to external web hosting has made it possible to finally create an RSS feed for this site. Note that the content itself is not part of the feed, only the headers and a corresponding link back to this site.

Link: RSS Feed

Topic: General, by Kjetil @ 01/09-2019, Article Link

New Web Hosting

After 12 years of hosting this site on a server in my own house I have decided to finally move it to an external web hosting site. Hopefully this will provide better uptime, as it does not rely on my own Internet connection.

Direct Link:

Topic: General, by Kjetil @ 22/08-2019, Article Link

OpenVPN Setup for Android

There are probably many ways to do this, but this is what worked for me in the end, after several trials and errors. I ended up making a "standalone" server solution based on running in GNU Screen to avoid messing too much with my existing server.

I started by downloading the EasyRSA scripts to help generating certificates and such. Then ran the following commands:

./easyrsa init-pki
./easyrsa build-ca
./easyrsa build-server-full server
./easyrsa build-client-full client
./easyrsa gen-dh

You will have to enter a CA key passphrase and PEM passphrase, keep those for later.

Once the files are created, copy them into a new location where everything will be stored, in my case the "openvpn" directory under my home directory:

mkdir ~/openvpn
cp pki/ca.crt ~/openvpn/
cp pki/dh.pem ~/openvpn/
cp pki/issued/client.crt ~/openvpn/
cp pki/issued/server.crt ~/openvpn/
cp pki/private/ca.key ~/openvpn/
cp pki/private/client.key ~/openvpn/
cp pki/private/server.key ~/openvpn/

The OpenVPN server configuration file must be created manually, at ~/openvpn/server.cfg with the following contents:

ca ca.crt
cert server.crt
key server.key
dh dh.pem
dev tun
port 1194
proto udp
push "redirect-gateway def1 bypass-dhcp"
push "dhcp-option DNS"
push "ifconfig"
mode server
verb 4
client-config-dir ccd

Create a new directory "ccd" under the directory structure and create the file ~/openvpn/ccd/client with the following single line:


To be able to start things easily and open the necessary parts of the firewall a script like this can be used, placed at ~/openvpn/

screen -S openvpn -d -m sudo openvpn server.cfg

sudo iptables -A INPUT -p udp --dport 1194 -i eth0 -j ACCEPT
sudo iptables -A INPUT -i tun0 -j ACCEPT
sudo iptables -A FORWARD -i tun0 -j ACCEPT
sudo iptables -A FORWARD -i eth0 -d -j ACCEPT

This particular server already has iptables setup for NAT and such, so that is not present in this configuration.

Finally, the Android OpenVPN application requires a matching "ovpn" file with the client configuration. I had to make this one by manually looking something like this:

dev tun                             
proto udp
remote 1194
resolv-retry infinite
verb 3
<contents of client.crt file>
<contents of client.key file>
<contents of ca.crt file>

Topic: Configuration, by Kjetil @ 18/08-2019, Article Link

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