Situation: I’ve taken about 50ish measurements on an FSH4 spectrum analyser saving a dataset of each using the save data function of the spectrum analyser.
Turns out: The R&S InstrumentView application does not install on Wine. So, how do I get the screenshots embedded in the saved datasets? Right: Search for the PNG magic number and a chunk end.
This is really sketchy but worked on all measurement files. If you’re in the same situation, just check out my repository.
As discussed in [Insanity4004]’s excellent blog post, Xilinx packages their ISE and SDK suite with the necessary libraries (like Qt4 for example). Unfortunately, some seem to be missing and cause errors that are rather cryptic for the lay(wo)man.
In addition to providing libpng and libfreetype, I’ve noticed that in order to start the SDK (xsdk, part of the EDK package), you need to provide an older version of libcairo as well.
With the standard installation, starting xsdk results in:
[...]/EDK/bin/lin64 $ ./xsdk
Xilinx Software Development Kit
Xilinx EDK 14.7 Build EDK_P.20131013
Copyright (c) 1995-2012 Xilinx, Inc. All rights reserved.
Eclipse:
An error has occurred. See the log file
[...]/.eclipse/com.xilinx.sdk.product_1.0.0_1005998729/configuration/1655967348948.log.
[...]/EDK/bin/lin64 $ cat [...]/.eclipse/com.xilinx.sdk.product_1.0.0_1005998729/configuration/1655967348948.log
!SESSION 2022-06-23 08:55:48.743 -----------------------------------------------
eclipse.buildId=Release 14.7 Build SDK_P.20131013
java.version=1.6.0_21
java.vendor=Sun Microsystems Inc.
BootLoader constants: OS=linux, ARCH=x86_64, WS=gtk, NL=de_DE
Command-line arguments: -os linux -ws gtk -arch x86_64
!ENTRY org.eclipse.osgi 4 0 2022-mm-dd hh:mm:ss.605
!MESSAGE Application error
!STACK 1
java.lang.UnsatisfiedLinkError: Could not load SWT library. Reasons:
[...]/.eclipse/com.xilinx.sdk.product_1.0.0_1005998729/configuration/org.eclipse.osgi/bundles/243/1/.cp/libswt-pi-gtk-3836.so: /lib/x86_64-linux-gnu/libcairo.so.2: undefined symbol: FT_Get_Var_Design_Coordinates
no swt-pi-gtk in java.library.path
Can't load library: [...]/.swt/lib/linux/x86_64/libswt-pi-gtk-3836.so
Can't load library: [...]/.swt/lib/linux/x86_64/libswt-pi-gtk.so
[...]/.swt/lib/linux/x86_64/libswt-pi-gtk-3836.so: /lib/x86_64-linux-gnu/libcairo.so.2: undefined symbol: FT_Get_Var_Design_Coordinates
at org.eclipse.swt.internal.Library.loadLibrary(Library.java:331)
at org.eclipse.swt.internal.Library.loadLibrary(Library.java:240)
at org.eclipse.swt.internal.gtk.OS.<clinit>(OS.java:22)
at org.eclipse.swt.internal.Converter.wcsToMbcs(Converter.java:63)
at org.eclipse.swt.internal.Converter.wcsToMbcs(Converter.java:54)
at org.eclipse.swt.widgets.Display.<clinit>(Display.java:133)
at org.eclipse.ui.internal.Workbench.createDisplay(Workbench.java:695)
at org.eclipse.ui.PlatformUI.createDisplay(PlatformUI.java:161)
at org.eclipse.ui.internal.ide.application.IDEApplication.createDisplay(IDEApplication.java:154)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:96)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:353)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:180)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:629)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:584)
at org.eclipse.equinox.launcher.Main.run(Main.java:1438)
at org.eclipse.equinox.launcher.Main.main(Main.java:1414)
The reason is not too hard to find, but the error message is a mouthfull. The important bit is
java.lang.UnsatisfiedLinkError: Could not load SWT library. Reasons:
[...]
/lib/x86_64-linux-gnu/libcairo.so.2: undefined symbol: FT_Get_Var_Design_Coordinates
Which basically means: I am looking for libcairo, found it on your system, but the symbol (call, function, whatever) named FT_Get_Var_Design_Coordinates does not exist there.
I have not investigated the reasons for this further. I assume, this function got renamed, moved, dropped since 2013. So I followed the recipe proposed in the blog post mentioned in the beginning:
Move it to your [...]/EDK/lib/lin64 folder. In my case this is /opt/Xilinx/14.7/ISE_DS/EDK/lib/lin64.
I fear I might run into these issues again and again since we’re stuck here with a Virtex-6 device. I wonder if SymbiFlowF4PGA are working on a 6-series toolchain. That’d certainly create some resilience against the future.
Small side note I: The 6-series system here is supposed to replace an analogue RF control system that was in service for 30-something years. People were reluctant to switch to digital because of fears of this (what you see above): Toolchains being very complex and not working anymore after only a couple of years, vendors dropping support (well, Xilinx technically did not drop it entirely, but they’ve certainly not fixed library dependencies or checked that they ship their programmes with the old versions).
Small side note II: The fact that I can just (1) go to a trusted repository of old packages (Ubuntu’s Launchpad), (2) grab a package file, (3) extract an old shared library file, and (4) drop it in place without breaking my whole system, is a pretty awesome feature of Linux systems. I know for a fact that other platforms (yeah, looking towards the Seattle area) struggle with steps 1 and 4.
Post scriptum I: Trying to start xilhelp revealed three more libraries missing. libXp.so.6 (get it here), libXm.so.4 (run apt install libxm4) and libstdc++5 (you’ll have to go back to Ubuntu 14.04 Trusty for that). But ended in a SEGFAULT *sigh*.
Post scriptum II: Way more is broken than I had estimated! All Tcl-based scripts (that is: all IP Core generators) need libtcl8.4, obviously, duh! So, well get libtcl8.4.so from Ubuntu 16.04. At least, now the license wizard is opening up. But that causes all sorts of other problems with Tcl. I suppose it’s because no packages are installed in any way. Let’s say: ISE 14.7 is severely broken on newer systems. Way out 1: A VM with Ubuntu 14.04 or 16.04 (yikes!). Way out 2: F4PGA, maybe!?
SymPy allows quick and (relatively 😜) easy manipulation of algebraic expressions. But it can do so much more! Using the sympy.physics.control toolbox, you can very inspect linear time-invariant systems in a very comfortable way.
I was looking at a paper (Janiszowski, 1993) which features three transfer functions of different properties and wanted to look at their pole-zero diagrams as well as their Bode plots in real frequency. The transfer functions where the following:
(1)
Drawing the pole-zero diagrams from this representation is easy:
Zeros: Set numerator to zero
Poles: Set denominator (or its individual terms) to zero
Drawing the Bode diagram however would’ve involved some basic programming. But neither is necessary.
import sympy as sy
from sympy.physics.control.lti import TransferFunction as TF
from sympy.physics.control import bode_plot, pole_zero_plot
s = sy.symbols("s", complex=True)
G1 = (2 + 42*s)/((1 + 2*s)*(1 + 40*s))
tf = TF(*G.as_numer_denom(), s)
bode_plot(tf)
pole_zero_plot(tf)
Bode plot of the transfer function G1(s)
Pole-Zero diagram of the transfer function G1(s)
Well, that was easy. TransferFunction (abbreviated with TF in my examples) requires numerator and denominator to be passed as separate arguments. sympy_expr.as_numer_denom() is convenient, as it returns a (numerator, denominator) tuple. Using the asterisk expands this.
Now, what else can we do with this? Look at RLC resonators, for example:
A parallel resonator of resistance R, inductance L and capacitance C
The reactance of the inductor and capacitor are given by
(2)
where s is basically the complex frequency (we’re looking at this with Laplace eyes). Now, off to SymPy we go:
R, C, L = sy.symbols("R, C, L", real=True, positive=True)
Xc, Xl = 1/(s*C), s*L
def par(a, b):
# Shorthand for a parallel circuit
return a*b/(a+b)
G = par(Xc, par(R, Xl)).ratsimp()
G = G.subs({R: 1e3, L: 1e-6, C: 1e-6})
tf = TF(*G.as_numer_denom(), s)
bode_plot(tf, 5, 7)
pole_zero_plot(tf)
Why is this useful? Well, because it is quick and robust and once you have your transfer function typed out, you get the impulse and step responses for free:
import sympy as sy
from sympy.physics.control import impulse_response_plot
from sympy.physics.control import step_response_plot
s = sy.symbols("s", complex=True)
G1 = (2+42*s)/((1+2*s)*(1+40*s))
G2 = (5-60*s)/((1+4*s)*(1+40*s))
G3 = 4*(1+s)/(1+4*s+8*s**2)
for G in [G1, G2, G3]:
tf = TF(*G.as_numer_denom(), s)
bode_plot(tf)
pole_zero_plot(tf)
step_response_plot(tf, upper_limit=60)
impulse_response_plot(tf, upper_limit=60)
Note: SymPy’s adaptive plotting is not particularly good at plotting oscillations, so the impulse response of the RLC circuit above will look ugly.
There are various possible ways you can lose access to your Gitea instance. In particular, if you are getting user accounts via LDAP, you should always have a key to get back in: a “local” admin.
In case you haven’t got one (totally not like I did definitely only once 🤫), deleted it or lost its password, here’s the procedure in to variants: running on plain Linux, and running within Docker.
Plain Linux
List the available (local) user accounts (you may need to run this with sudo):
$ gitea admin user list
ID Username Email IsActive IsAdmin
1 user1 me@home.earth true false
You may not get a single user listed here. In order to add a local administrator, do this
$ sudo gitea admin user create --username local_admin --email admins@email.earth --admin --random-password
generated random password is 'IzgvOwv1M9EG'
New user 'local_admin' has been successfully created!
$ sudo gitea admin user list
ID Username Email IsActive IsAdmin
1 unpriv_local bowfingermail@gmx.net true true
3 local_admin admins@email.earth true true
Especially on shared machines, I’d strongly recommend not setting a password via the command line. It’ll stick in bash_history and may be visible in the process list. Hence the --random-password option here. Use the generated password upon first login in the browser.
Docker Container
In order to get to the “plain Linux” field, you simply run a bash in the Gitea Docker container.
What’s the container’s name? Get it via docker container ls -a. Let’s say it’s called gitea. To start bash in that container, do
user1@linux:$ docker exec -it gitea /bin/bash
Now, you basically do the same thing as in the section above.
docker # gitea admin user list
ID Username Email IsActive IsAdmin
1 user1 me@home.earth true false
docker # gitea admin user create --username local_admin --email admins@email.earth --admin --random-password
generated random password is 'ikV6xzPTiH7B'
New user 'local_admin' has been successfully created!
docker # gitea admin user list
ID Username Email IsActive IsAdmin
1 unpriv_local bowfingermail@gmx.net true true
3 local_admin admins@email.earth true true
Conclusion (and Other Platforms)
The Plain Linux approach works equally well on other platforms. I hope this helps.
Back in uni me and control systems never really clicked. So I took a dive into the topic as I had the time. Long story short for all who know equally little or even less about the maths of control systems as I do:
Often, you model control systems using the Laplace transform. That’s nice and good for continuous systems.
Once you’re going to the discrete (digital) world, you want to use the Z-transform.
There is a (complicated) relation between Laplace domain and Z domain.
There are approximations, using a complex maps to map from Laplace to Z domain (a bilinear transformation, Tustin’s method, being the one used here).
This is a post on serendipity, because what this is about is actually neither control systems, Z-, or Laplace transforms but a numbers game. Bare with me.
Many systems can be modelled using a rational function of the form
You can easily put this into sympy and play around with it.
import sympy as sy
s, z, Ts = sy.symbols("s, z, T_s")
a0 = sy.S.One
a1, a2 = sy.symbols("alpha_1, alpha_2")
b0, b1, b2 = sy.symbols("beta_0, beta_1, beta_2")
G = (b0 * s**2 + b1 * s + b2) / (a0 * s**2 + a1 * s + a2)
G # use `print(sy.latex(G))` to get the LaTeX representation
Nice. Let’s generalise this a little bit:
import sympy as sy
s, z, Ts = sy.symbols("s, z, T_s")
N, M = 2, 2
a = sy.symbols(f"alpha_1:{N+1}")
a = (sy.S.One, *a)
b = sy.symbols(f"beta_0:{M+1}")
G = sy.Add(*[b[i] * s**i for i in range(M+1)]) / sy.Add(*[a[i] * s**i for i in range(N+1)])
By playing with the values for N and M we can now generate any order of rational function we wish. Again, not the thing this article is about.
Then there is the bilinear transform called Tustin’s method that approximately maps the function G from the Laplace domain into the Z domain.
Sweet. Now, I want to have the representation in two polynomials in z (numerator and denominator) to extract the coefficients (because that’s what I wanted to hack into code):
num, den = G.as_numer_denom()
num = sy.Poly(num, z)
den = sy.Poly(den, z)
num.coeffs()
den.coeffs()
… but my eye spotted a pattern here. Do you see it? It’s easier to see in matrix representation, and I’ll only look at num (i.e. the expression with βi in it, because I set É‘0 to 1):
Here is the resulting matrix for N = M = 3 and for N = M = 5:
Here are the resulting matrices for N = M = 4:
Here are the resulting matrices for N = M = 6
The odd values for N and M produce matrices with all non-zero values, so I’ll look at those first.
What I find stunning is the fact that there are so many patterns and yet I fail to think of a pattern that creates the whole matrix. For example, the first column clearly follows the binomial distribution:
where k is the row number starting with 0.
The first and last rows of the matrix are power series of 2 and -2 respectively:
where l is the column number starting at 0.
Every column has a different sign pattern starting at all positive on column 0 and alternating, starting with + on the last column.
Ignoring the signs, the columns are related like this
N
#0 ↷ #N-1
#1 ↷ #N-2
#2 ↷ #N-3
#3 ↷ #N-4
3
྾ 8
྾ 2
5
྾ 32
྾ 8
྾ 2
7
྾ 128
྾ 32
྾ 8
྾ 2
What multiples relate the lth column from the left with the lth column from the right, ignoring the sign.
Maybe this follows from the power series mentioned earlier. But looking at the coefficients in each column the binomial pattern is lost as you move to the inside.
And last but not least wild zeros appear when you look at the even values for N and M:
Apparently, in the middle row as well as the middle column, every other value is zero.
All right, I’m absolutely sure mathematicians and control systems theoreticians have looked at this back in the day and this is all solved and done. Still, I found it interesting to look at.
If you want to create those values yourself, you can use this little script, and modify N and M. But beware, at N = 10 the script runs for 10 seconds.
import sympy as sy
s, z, Ts = sy.symbols("s, z, T_s")
N, M = 3, 3 # <-- Modify here
a = sy.symbols(f"alpha_1:{N+1}")
a = (sy.S.One, *a)
b = sy.symbols(f"beta_0:{M+1}")
G = sy.Add(*[b[i] * s**i for i in range(M+1)]) / sy.Add(*[a[i] * s**i for i in range(N+1)])
tustin = 2/Ts * (z-1)/(z+1)
G = G.subs({s: tustin}).simplify()
num, den = G.as_numer_denom()
num = sy.Poly(num, z)
den = sy.Poly(den, z)
for l in num.coeffs():
p = sy.Poly(l, Ts)
for i, B in enumerate(p.all_coeffs()):
try:
coeff, _ = B.as_two_terms()
except:
coeff = 0 if B is sy.S.Zero else 1
print(f"{repr(coeff):6s} & ", end="")
print()
Oh, and of course you can change N and M independently from each other, but I could not be bothered to look at this as well.
I’ve come across a situation where out of three docker containers that should be running, only one was shown by docker container ls -a. Weird, hu?
The missing two were clearly running their processes because the web service they provided was active and reachable.
After a lot of forth and back, it turned out that Ubuntu 20.04 with snap came with a docker snap – and had a recent Docker CE installed via the apt package manager. Don’t do that.
Once the snap docker was removed, it worked and showed all the containers again.
Upon upgrading my Kernel on my Ubuntu 20.04 LTS to the HWE stack, I ran into the issue that Wifi stopped working.
Turns out, it only refused to listen/transmit on channels 12 and higher. My router was using channel 13, so no luck.
After some research, I found that you can set the Wifi stack to obey your country’s regulatory requirements. In Germany, channels 12 and 13 are fine to use.
In my case, with a Qualcomm Atheros AR93xx using ath9k, editing /etc/default/crda setting REGDOMAIN=DE or trying to use iw reg set DE did not help.
What helped after all was setting ieee80211_regdom=DE when loading the cfg80211 module. So, I somehow doubt that the issue was the ath9k module itself.
Try this:
Create /etc/modprobe.d/cfg80211.conf with content:
options cfg80211 ieee80211_regdom=DE
Obviously, you set it to the 2-digit ISO code of the place you live at.
For Germany, this results in the expected 2.4 GHz band channel list (iw list | grep -A 15 Frequencies:):
A while ago, I wanted to add more space to my MD+LVM2 array on a Linux machine (Ubuntu 20.04 at the moment). The setup used MD to make a RAID1 of two HDDs and knowing that I would eventually like to add more storage later, I put LVM2 on top.
A Card That Doesn’t Work
The moment came but I realised my mainboard did not have enough SATA ports. So, after some research, I bought a HighPoint Rocket 640L PICe SATA host adapter which comes with a Marvell 88SE92xx series chip (88SE9230 in my case).
Tl;dr: Don’t.
It took me half a day of research to figure out that (as of September 2021 and Linux kernel 5.4, but I tried 5.14 too) it would not show disks at all if IOMMU was activated. Also, it did not like stand-by/hibernation: HDD 4 would spin up fine on boot, but would not show up after a stand-by rendering the RAID incomplete, and the LVM volume in read-only mode. Which is a nice safeguard, thanks LVM-developers! But still annoying as such of course.
A Card That Does Work
So, I did more research and found the Delock 5x SATA PCIe x4 Card featuring a JMicron Technology chip (with an ID [197b:0585]). And guess what:
All disks come back after stand-by/hibernation
IOMMU and virtualisation can be switched on, no problem
It even has one more port than the HighPoint card
Disclaimer: All this may change in the future. I have no idea if this is a driver problem or a problem with the chip. But I though it might save some of you time.
Conclusion
Don’t use Marvell 88SE92xx series, at least in a Linux system. Full stop.
So, I have this Samsung NP900X3A laptop that I used for about 4 years. It started to have random glitches when I was about to start some very important work, so I decided to get a new laptop. I never sold or scrapped it, and recently I took it out of its neoprene bag, cleared the disk, installed a clean Ubuntu 20.04 and it worked like a charm…
…ish. Well, obviously it’s old, the battery had seen better days, but for work when it’s on power supply, it is a very decent device. Until recently:
I plugged it in, opened the lid, pressed power aaaand: it won’t boot.
Okay, my first though: The SSD died. Nothing catastrophic, a 120 GB mSATA costs about 45 €. So I booted into a Linux live system, quickly installed smartmontools (smartctl), opened my favourite smartctl reminder wiki page (seriously, man pages are still the best, but they’re so long!), and found that all tests passed. Well, the drive was old, yes, but still intact. fsck did not complain either.
But it still wouldn’t boot.
So, I opened the BIOS menu. First suspect: time and date were off by years. Aha! The BIOS battery, or actually, the battery for the real time clock (RTC), had died. And that set everything to defaults. Including: UEFI [DISABLED]. Well, you could’ve printed something, you nob…
Anyways: Enabled it, it boots again.
Here’s the culprit: Empty, unmarked
So, what about the battery? It’s obviously a coin cell on two wires with a plug. Nice idea, very accessible. Really. But at least some documentation would have been nice. No label, no print, nothing.
Measuring reveals: diameter 16 mm, thickness maybe a little below 2 mm. Hard to tell exactly while still in the rubber protection. So, could it just be a CR1616 or CR1620 cell with some spot welded soldering pins enclosed in some heat-shrink tubing?
No way to get the original part anymore. Samsung stopped selling laptops for quite a while in Germany (or even the whole EU, though it may have recently restarted again). Ebay has some offers. Anything from 5 to 150 € (seriously, it’s a coin cell, who charges more than 10 € for that?).
I decided to get one full package (cell, heat-shrink, wires and connector) for 5 € and a bare cell with spot welded solder pads for 2 €.
Got the wrong cell for 5 € (for a Samsung P20). Would’ve fit if it wasn’t for the connector.CR1616 for 1,59 € to the rescue!
So, where’s the rant? Here:
COMPLEX ELECTRONIC DEVICES “BREAK” BECAUSE OF < 5 € COMPONENTS AND YOU NEED A F****ING PhD IN BATTERIES AND EBAY TO FIND REPLACEMENT PARTS BECAUSE NOONE THOUGHT OF PRINTING “CHECK UEFI SETTINGS” OR OF PRINTED LABELS ON A BATTERY OR A SIMPLE REMARK IN THE USER MANUAL (“YEAH, AND BTW, THE BATTERY IS A CR1616 FOR 84 CENTS WITH A MOLEX CONNECTOR, YOU’RE WELCOME.”)???
By now, this laptop would’ve been thrown out twice by every single average capable consumer in the world. And honestly, I cannot blame them. Right to repair will have a loooooong way to go.
So yeah: Turns out the coin cell actually was a CR1616.
Cut off the wires, placed heat-shrink, soldered to replacement cell (not to the cell directly but to the solder tails), pack all in heat-shrink and voilà : a 1,65 € (+some solder and heat-shrink) replacement for a 10 year old laptop.
