I'm trying to send files over a half-duplex interface (RS-485) between a box PC running debian (4.19) and a SBC with an im6xDL.
Thanks to this community I can successfully transfer simple data between the units using picocom or by echoing/reading.
The box PC supports half-duplex RS-485 natively and has automatic RTS functions so that you can read/send data without any issue. The SBC on the other hand needs to be toggled to change into RX or TX mode.
This turned out to be a problem when I tried to send files from the box PC to the SBC.
On the box PC:
picocom /dev/ttyUSB0 -b 9600 -fn
C-a,C-S
***file: /home/user/test.txt
Transfer incomplete
*** exit status: 128
On the SBC
picocom /dev/ttymxc2 -b 9600 -fn -et
C-a,C-r
Terminal ready
�000000
As you can see something is terribly wrong, it is like it cannot interpret the bits when a file is being transferred.
My questions:
Is it possible to send files from the command line in half-duplex systems? (The SBC needs to be in RX mode the entire time).
Is there another way to achieve this that is more intuitive?
As always, thanks for the help and support :)
/W
See here:
Pymodbus - Read input register of Energy meter over rs485 on uart of raspberry pi3
The solution I presented there using pylibmodbus should work for any hardware with UART and one or two GPIO lines accessible from user space in Linux.
If, on the other hand, what you want to do is use something like picocom or minicom then you can take a look at the hardware-only solution using a 555 timer.
Of course, if prototyping circuits is not for you, you can always buy a USB to RS485 with half-duplex support. You have many available but those based on the MAX13487 IC seem to work very well.
EDIT: The solution using the 555 timer is not in the post I linked above but here together with some more background material on half-duplex RS485 links: RS485: Inappropriate ioctl for device
I'm reading The TTY demystified, trying to get some understanding about tty, pty.
After reading the first half. I'm not getting the complete picture of how the whole thing is working when I'm type some commands into an xterm or ssh.
Below is the picture visualizing my understanding, I don't know if it's correct or not, please help verify.
when I type a command on the keyboard
keyboard ->tty->xterm->pty(master)->pty(slave)->user processes
(the purple line)
when a user process generates some output
user processes->pty(slave)->pty(master)->xterm->tty->display
(the blue line)
The diagram seems confused with regard to the box for "tty":
a pseudo-terminal has devices that might be named "tty" and "pty" (in the pre-Unix98 configuration). The /dev-entry for tty corresponds to the pseudo-terminal master.
xterm reads keystrokes as X events via the X server from whatever the keyboard device happens to be.
I have a 40x7 VFD that functions as a serial terminal. It has a dedicated keypad that provides hex-entry, however, I would like to use a keyboard for the standard input. Basically, I want to be able to use the VFD as a display for a Linux bash prompt, but use the keyboard connected to the computer as the means of input. Instead of connecting a monitor, the serial terminal will be the monitor. I can get the login prompt displayed on the VFD with agetty, but since it only has hex-entry, how can I change where the system is looking for standard input?
Thanks,
Core_Module
I think the best method would be to create a pseudo terminal. In doing so you create a fake terminal device with a /dev/pts/[n] name that acts like a real input/output device. A program could connect the console (keyboard) as input and the VFD as output and send and receive that data over the pseudo device. You can then point agetty at the /dev/pts/[0] device instead of a /dev/ttyS[n] device. Some ideas on doing this can be found in many tutorials online. From the link:
A pseudo-terminal is a pair of character mode devices also called pty. One is master and the other is slave and they are connected with a bidirectional channel. Any data written on the slave side is forwarded to the output of the master side. Conversely, any data written on the master side is forwarded to the output of the slave.
I found another StackOverflow question that may also be of assistance. See this link. It could be adapted to suit your needs.
The primary video card usually can be set in the BIOS (option Primary VGA card), and it will be the first card used by the system.
My question is how can I programmatically identify (using a shell script and utilities is preferable) which of my two video cards is the primary card?
Edit: I was hoping that I wouldn't have to elaborate why I need this, because it is a bit complex, but I will explain the problem below.
I have a configuration wizard which allows the dynamic configuration of a multiseat system in a LiveCD, with two independent displays, keyboards and mice, my wizard works in this way:
Start one Xorg server per video card (after generating xorg.conf with the correct PCI bus ID).
Start a ui in each of Xorgs with messages for configuration (press key and press mouse). One seat can be configured each time.
After the first seat is configured, the wizard closes the first Xorg and start the definitive Xorg in this seat with the desktop environment (already with the correct keyboard and mouse set).
The second seat now is able to be configured (press key and mouse), after this pass 3 is repeated for seat two.
The problem is: If I start the first Xorg in the primary video card, everything works, but if I start the first Xorg in the secondary card this is what happens:
The passes 1, 2, and 3 works, but at the end of pass 3, when the Xorg of the first seat is closed, the Xorg of the second seat blinks and doesn't come back, just show a blank screen with a _ cursor at top, the desktop of the first seat loads, but I don't see the wizard screen in the second seat, the first Xorg just comes back if I execute a kill -HUP , and I need to start the ui from it again.
So, it is why I need to identify the primary video card before I can start Xorg (sorry I didn't mention this before). I tested this system in different computers, with different video cards and the behavior is the same. I also tested with the lasted packages of the kernel and Xorg in Ubuntu 12.04 (packages of the raring release).
Assuming X11 is running, you could suppose that primary card is the one used by Xorg... then you might try
ls -l /proc/$(pidof X)/fd |grep /dev/dri
on my system Debian/Sid/x86-64 with Linux 3.12 kernel (which has an Nvidia card on a Intel3770K which also has its VGA) I'm getting /dev/dri/card0 etc...
But you should explain really why you are asking and what problem do you want to solve.... Why does that matter to you?
I am not at all sure that Linux has a notion of primary graphic card like the BIOS knows it.
And probably hwinfo is telling you everything about your graphical cards.
There are several command line tools in Linux that give you human readable information from the BIOS. Maybe you can find your Video boards in there and see which one is made primary. From what I see in my output, it does not look like something says "this is the primary video", but I do see quite a lot of information. You could output that information to a file when video card A is primary, again when B is primary, then compare those two files and see whether there is a difference.
The command I used, which gives me a lot of information, is dmidecode:
sudo dmidecode | less
If you look at the manual page:
man dmidecode
You will notice that the programmers offer a few other similar tools such as biosdecode and vpddecode.
From those you learn that the BIOS information is available from the /dev/mem device. Although you need to be root to read it, if you know the address (I don't) then you could go in there and peek and poke as required to find out where that one information of which video card is defined as the primary video card.
Running dmidecode, there are some details about my motherboard:
Handle 0x0002, DMI type 2, 15 bytes
Base Board Information
Manufacturer: Supermicro
Product Name: X9SCI/X9SCA
Version: 1.01
Serial Number: ZM25U44192
Asset Tag: To be filled by O.E.M.
Features:
Board is a hosting board
Board is replaceable
Location In Chassis: To be filled by O.E.M.
Chassis Handle: 0x0003
Type: Motherboard
Contained Object Handles: 0
Here I have one video entry:
Handle 0x000E, DMI type 10, 6 bytes
On Board Device Information
Type: Video
Status: Enabled
Description: To Be Filled By O.E.M.
Then the other entry looks like this:
Handle 0x0036, DMI type 41, 11 bytes
Onboard Device
Reference Designation: Onboard IGD
Type: Video
Status: Enabled
Type Instance: 1
Bus Address: 0000:00:02.0
It could also be something you need to read from the Flash memory your BIOS uses. This is done with flashrom (that you may need to install):
sudo flashrom --programmer internal --read my-flash.bin
In my case the ROM on my computer is 2Gb of data. So quite large. However, you can be sure that the information you are looking for exists within that data block since that is the only mean for the BIOS to save data that will stay around when the computer gets turned off.
I have found a way how to check the primary GPU when they are from different vendors or at least have different names.
In KDE go to Info Center, then open Graphics -> OpenGL. In Direct Rendering (GLX) and Direct Rendering (EGL) you can see a Driver block. You can see the Vendor and Device there. It will name the GPU which is primary.
At this screenshot you can see that AMD gpu is primary:
Also, you can get that Vendor value programmatically by running
glxinfo | grep "OpenGL vendor string" | cut -f2 -d":" | xargs.
I guess this method will stop working when kde will switch to vulkan for rendering (in kde 6). But for now I do not know another method of determining primary gpu.
What is the best way to capture HID input on linux for games? I don't need anything special. Just mouse and keyboard. Right now I'm using Xlib. I have a separate input thread, which has its own connection to the X Server (Display instance) and it handles events for main render window. It is working just fine, but it is a bit limited. For example, I'm missing mouse raw input.
Have you tried opening and reading device files in /dev/input?