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by jojopi
Mon Jun 17, 2019 1:53 pm
Forum: Off topic discussion
Topic: how heavy is raspbian ?
Replies: 30
Views: 851

Re: how heavy is raspbian ?

Given that the Pi and it's SD card will be electrically neutral no matter if the SD is programmed on blank, it will always have the same mass. The charges on those gates are balanced elsewhere. Certainly in a regular capacitor we would expect the electrons added to the negative plate to be closely ...
by jojopi
Fri Jun 14, 2019 1:49 am
Forum: Beginners
Topic: USB Numeric Keypad with RPI3
Replies: 4
Views: 113

Re: USB Numeric Keypad with RPI3

Note, a regular keyboard will control the PDF document as inteneded with the stand alone directional arrows but now with arrows on keypad, something we failed to note during first attempts. So, the unspecified application you are running treats the keypad arrows differently than the dedicated arrow...
by jojopi
Sat May 25, 2019 6:18 am
Forum: General discussion
Topic: Incorrect mapping of the 79 keys official keyboard
Replies: 8
Views: 552

Re: Incorrect mapping of the 79 keys official keyboard

It does seem strange to go with a hybrid layout that is not completely supported in the recommended operating system. However, the initial announcement last month said that these keyboards can report their country to the host, so maybe RPF/T plan to add software to configure them at some point. Out ...
by jojopi
Wed May 22, 2019 7:01 pm
Forum: Networking and servers
Topic: UnicodeDecodeError: 'utf8' codec can't decode byte 0x92 in position 532: invalid start byte
Replies: 5
Views: 344

Re: UnicodeDecodeError: 'utf8' codec can't decode byte 0x92 in position 532: invalid start byte

The error corresponds to the fancy apostrophe (right single quotation mark) in "the system’s owner". That would be 0x92 in legacy single-byte Windows encodings, such as CP1252. In UTF-8 it should be the three byte sequence e2-80-99. Alternatively it could be replaced with a non-fancy ASCII apostroph...
by jojopi
Wed Apr 17, 2019 1:57 pm
Forum: Troubleshooting
Topic: Environment variables vs. bash and lxterminal
Replies: 2
Views: 144

Re: Environment variables vs. bash and lxterminal

(Weirdly, I did `ls -lut ~/.bash*` and none of them seemed to have been accessed recently!) You cannot rely on access times. Many distros and images mount filesystems with the "noatime" or "relatime" options by default. Especially on an SD card, where small writes are costly, frequent access time u...
by jojopi
Tue Apr 02, 2019 12:13 am
Forum: C/C++
Topic: ATEXIT behavior
Replies: 17
Views: 2093

Re: ATEXIT behavior

dlclose returns and atexit calls function. By that time linux has not yet removed library. No, the function registered via atexit is called during the dlclose, before dlclose returns. By the time dlclose returns, the library and function have been removed from the address space. (POSIX does not gua...
by jojopi
Mon Apr 01, 2019 11:42 pm
Forum: Python
Topic: For Loop
Replies: 1
Views: 168

Re: For Loop

Simpler examples: for i in "abc": print(i) for i in [1,2,3]: print(i) for i in "abc", [1,2,3]: print(i) In the first case there is a string, and for iterates over the characters in the string. In the second case there is a list, and for iterates over the objects in the list. In the third case there ...
by jojopi
Mon Apr 01, 2019 10:46 pm
Forum: Advanced users
Topic: crontab and DST issue
Replies: 4
Views: 291

Re: crontab and DST issue

The job ran at the correct time, and cron jobs by default use the same timezone as cron itself. The date argument "last month" means the same as "1 month ago", or "now -1 month". The month is subtracted without changing timezone/dst values. (I am not sure if that is really as intended, and the docum...
by jojopi
Sat Mar 30, 2019 9:09 am
Forum: C/C++
Topic: ATEXIT behavior
Replies: 17
Views: 2093

Re: ATEXIT behavior

"man atexit" says that since glibc 2.2.3, functions registered from within a shared library will be called when the library is unloaded. This resolves the potential crash of trying to call them after they have been unmapped. Putting a sleep() between dlclose() and exit(), this is indeed what is happ...
by jojopi
Mon Feb 11, 2019 5:32 am
Forum: Debian
Topic: Porting Debian ARM to the Raspberry Pi
Replies: 8
Views: 1895

Re: Porting Debian ARM to the Raspberry Pi

This thread is about porting vanilla Debian (not Raspbian) to the Raspberry Pi. My goal is to provide an armel image that boots on all Pi models, an armhf image that boots on the Pi 2 and 3, and an arm64 image that boots on the Pi 3. I would not call that porting Debian to the Raspberry Pi. I would...
by jojopi
Fri Feb 08, 2019 5:32 pm
Forum: Advanced users
Topic: Device Names of USB Serial ports
Replies: 4
Views: 327

Re: Device Names of USB Serial ports

There are standard udev rules that create predictably-named symlinks under /dev/serial/by-id/, based on the USB descriptors, and /dev/serial/by-path/, based on the physical port numbering. You will need to use by-path if the two devices are otherwise identical. The predictable names are a bit cumber...
by jojopi
Fri Feb 08, 2019 11:20 am
Forum: Beginners
Topic: how to delete accidently named files?
Replies: 5
Views: 260

Re: how to delete accidently named files?

Also: rm udo, then press [Tab⭾].

Tab completion is something you always want to be using for long file names, independent of whether they contain odd characters.

rm "udo or rm 'udo before pressing Tab will try to complete using quotes, instead of backslash escapes.
by jojopi
Fri Feb 08, 2019 8:36 am
Forum: Beginners
Topic: Remotely Changing Website Passwords
Replies: 2
Views: 126

Re: Remotely Changing Website Passwords

The key fob you are referring to would be something like RSA SecurID . That is a form of two-factor authentication, where to log in you need to both know the user's password and be in possession of their physical token. The token is designed so that it is impractical to extract the internal secret k...
by jojopi
Thu Feb 07, 2019 5:34 pm
Forum: Python
Topic: Deleting directory created by other user
Replies: 5
Views: 254

Re: Deleting directory created by other user

Write permission on a file allows you to modify the file. To remove or rename the file, you need write access to the containing directory. Similarly, write permission on a directory allows you to create and remove files inside it. To remove the directory itself you need write access to its parent. N...
by jojopi
Mon Feb 04, 2019 5:43 am
Forum: Python
Topic: Keyboard input
Replies: 13
Views: 903

Re: Keyboard input

Installation should be basically: sudo apt update sudo apt install python3-pip sudo pip3 install evdev The type field tells you if it is a key event or something else. The value field indicates whether a key event is up (0), down (1), or hold (2). I do not think there exist symbolic names for those ...
by jojopi
Sun Feb 03, 2019 2:23 pm
Forum: Troubleshooting
Topic: Cron Job running twice
Replies: 1
Views: 116

Re: Cron Job running twice

It is not running twice. The way the job is phrased, it requires two bash processes; one to set up the redirections and another to actually run the script. You could probably avoid that, but it is really not a significant cost. A bigger problem is that running cron jobs every single minute will prod...
by jojopi
Sat Feb 02, 2019 1:06 pm
Forum: Raspbian
Topic: Will there be a Devuan port for RPi1?
Replies: 23
Views: 5185

Re: Will there be a Devuan port for RPi1?

The images that will boot on Pi1/Zero are still armel, however. Expect them to be noticeably slower than Raspbian for anything that uses floating point. I also wonder whether Pi-specific stuff like the camera and various GPIO libraries will work. RPF/T have not supported armel userspace since the da...
by jojopi
Mon Jan 28, 2019 2:23 pm
Forum: Python
Topic: Keyboard input
Replies: 13
Views: 903

Re: Keyboard input

Python's struct module does not have a format character for the C type time_t. This makes it difficult to write a portable format string for parsing the event structure—we need to know whether time_t is 32bit or 64bit. The code in the original blog post will only work on 64bit Linux, and even then i...
by jojopi
Sun Jan 06, 2019 8:43 pm
Forum: Troubleshooting
Topic: Accidentally deleted Pi directory
Replies: 7
Views: 447

Re: Accidentally deleted Pi directory

I have accidentally deleted “Pi” directory inside ~/home Now I cannot login with user name pi and password “raspberry” You may not be able to log in using the GUI, but you should still be able to login in text mode. Press Ctrl+Alt+F2 to get to a text console: Raspbian GNU/Linux 9 raspberrypi tty2 r...
by jojopi
Sat Dec 29, 2018 4:23 am
Forum: C/C++
Topic: Little doubt on floating point precision
Replies: 7
Views: 763

Re: Little doubt on floating point precision

The Pi/Raspbian use IEEE754 binary floating point representation. The float type has 24 bits of precision, which is equivalent to around 7 significant digits in decimal. The double type has 53 bits, equivalent to 15 digits. A number such as 18736.845869 will be accurate enough if you calculate and s...
by jojopi
Tue Dec 18, 2018 3:05 pm
Forum: Bare metal, Assembly language
Topic: Unable to read directory content properly
Replies: 5
Views: 1155

Re: Unable to read directory content properly

I added an entry point: entry: ldr r0, =slash bl list_entries mov r7, #1 // _exit svc #0 slash: .asciz "/" Now strace shows: open("/", O_RDONLY) = 3 getdents(3, /* 16 entries */, 272) = 260 write(1, " 4 bin\0\n", 15) = 15 getdents(3, /* 5 entries */, 272) = 88 write(1, " 4 lost+found\0\275\n", 23) =...
by jojopi
Mon Dec 17, 2018 4:26 am
Forum: Bare metal, Assembly language
Topic: Unable to read directory content properly
Replies: 5
Views: 1155

Re: Unable to read directory content properly

How are you building this? There are undefined references to "utostr10" and "close_all", and no obvious entry point. If you have a complete binary, just run it in GDB, and it will tell you what instruction causes the SEGV and what values are in the registers. The Bare metal forum was renamed "Bare m...
by jojopi
Sun Dec 09, 2018 11:43 pm
Forum: Raspbian
Topic: Odd country, keyboard and language!
Replies: 7
Views: 1048

Re: Odd country, keyboard and language!

But neither Raspbian nor Debian will allow you to use a language and country combination which are not available as a supported locale. POSIX allows you to have a different locale for each category. Depending on exactly what OP intended, it may work to have France as the fallback locale, but overri...
by jojopi
Tue Apr 03, 2018 2:29 pm
Forum: Troubleshooting
Topic: Symbolic linked directories and ".." - why though?
Replies: 1
Views: 265

Re: Symbolic linked directories and ".." - why though?

This is a special feature of the shell's "cd" command. It keeps track of the path names used to get to your current directory, and by default it implements ".." by taking off the last component, instead of following the real ".." file on disk. You can also use "cd -P .." to go to the physical parent...
by jojopi
Mon Mar 26, 2018 6:28 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Accessing permission to open port /dev/ttyS0 for Serial communication
Replies: 8
Views: 11079

Re: Accessing permission to open port /dev/ttyS0 for Serial communication

[email protected]:~ $ sudo chmod 777 /dev/ttyAMA0 ACTION=="add", KERNEL=="ttyS0", MODE="0666" Let us not go crazy. 0666 or 0777 is never the right mode for anything. The problem here is that something else is using the device. That is why it is in group "tty" instead of "dialout". Disable serial shell in th...

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