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11-21-2020, 02:54 AM
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#1
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Member
Registered: Sep 2005
Location: Carpi (Modena) - Italy
Distribution: Ubuntu 20.04_x86_64 LTS; Slackware 13 64bit; Gentoo, Fedora, Yocto
Posts: 98
Rep:
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Raspberry Pi4 does not show on the HDMI the 3.5" TFT display output
Hello,
I would like to work with both the HDMI and the TFT display I have on my raspberry PI4.
I tried to configure the raspberry activating two framebuffer, but the result I have is that on HDMI I see only the log during the boot and on the TFT I see only X with the window manager.
What do I have to do to be able to work with both the displays? It does not matter if the diplays are cloned or not
Thanks
Claudio
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11-21-2020, 06:06 AM
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#2
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LQ Guru
Registered: Sep 2011
Location: Upper Hale, Surrey/Hants Border, UK
Distribution: One main distro, & some smaller ones casually.
Posts: 5,781
Rep: 
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When I attached two monitors, it automatically created an extended desktop, (I didn't touch config.txt at all).
(Mine were regular VGA screens.)
EDIT: Check this out - https://thepihut.com/blogs/raspberry...raspberry-pi-4
Last edited by fatmac; 11-21-2020 at 06:08 AM.
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11-22-2020, 08:42 AM
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#3
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Member
Registered: Sep 2005
Location: Carpi (Modena) - Italy
Distribution: Ubuntu 20.04_x86_64 LTS; Slackware 13 64bit; Gentoo, Fedora, Yocto
Posts: 98
Original Poster
Rep:
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I would like to make my tv smart connecting to it the raspberry.
The issue is that I have a 3.5" TFT and I would like to see the screen also on my tv using the HDMI.
I know that the two HDMI are working well together, but this is not my case.
What I see is similar to a condition where the TFT and the HDMI are two virtual desktops. On the TFT I see the graphic interface and on the HDMI I see the logs of the system.
This is my config.txt file
Code:
# For more options and information see
# http://rpf.io/configtxt
# Some settings may impact device functionality. See link above for details
# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1
# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
#disable_overscan=1
# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
#overscan_left=16
#overscan_right=16
#overscan_top=16
#overscan_bottom=16
# uncomment to force a console size. By default it will be display's size minus
# overscan.
#framebuffer_width=720
#framebuffer_height=450
# uncomment if hdmi display is not detected and composite is being output
hdmi_force_hotplug:0=1
# uncomment to force a specific HDMI mode (this will force VGA)
hdmi_group:0=1
#hdmi_mode=1
#hdmi_group=2
hdmi_mode:0=16
# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
hdmi_drive=2
# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
config_hdmi_boost=4
# uncomment for composite PAL
#sdtv_mode=2
#uncomment to overclock the arm. 700 MHz is the default.
arm_freq=800
# Uncomment some or all of these to enable the optional hardware interfaces
dtparam=i2c_arm=on
#dtparam=i2s=on
dtparam=spi=on
# Uncomment this to enable the lirc-rpi module
#dtoverlay=lirc-rpi
# Additional overlays and parameters are documented /boot/overlays/README
# Enable audio (loads snd_bcm2835)
dtparam=audio=on
[pi4]
# Enable DRM VC4 V3D driver on top of the dispmanx display stack
#dtoverlay=vc4-fkms-v3d
max_framebuffers=2
[all]
#dtoverlay=vc4-fkms-v3d
enable_uart=off
dtoverlay=tft35a:rotate=90
start_x=1
gpu_mem=132
Any suggestion?
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11-23-2020, 02:57 PM
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#4
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LQ Guru
Registered: Jan 2006
Location: Ireland
Distribution: Slackware, Slarm64 & Android
Posts: 17,278
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3.5" TFT? What's the dpi?
I suspect this line near the end of your quote from config.txt is odd
Code:
# uncomment if hdmi display is not detected and composite is being output
hdmi_force_hotplug:0=1
# uncomment to force a specific HDMI mode (this will force VGA)
hdmi_group:0=1
Specifically, 0≠1.
0 means disabled, 1 means enabled
It's inclined to be
option=0
or
option=1
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11-24-2020, 05:34 AM
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#5
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LQ Guru
Registered: Sep 2011
Location: Upper Hale, Surrey/Hants Border, UK
Distribution: One main distro, & some smaller ones casually.
Posts: 5,781
Rep: 
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Quote:
# uncomment to force a specific HDMI mode (this will force VGA)
hdmi_group:0=1
#hdmi_mode=1
#hdmi_group=2
hdmi_mode:0=16
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I think you probably need to set up your second moniitor....hdmi_group:1=
(If you are getting text, but no graphical screen.)
On the RPi4B you need to indicate which screen, hence the :0 or :1 on the hdmi_group statement.
Also, check menu > preferences > screen configuration to see what it has set.
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11-27-2020, 02:18 AM
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#6
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Member
Registered: Sep 2005
Location: Carpi (Modena) - Italy
Distribution: Ubuntu 20.04_x86_64 LTS; Slackware 13 64bit; Gentoo, Fedora, Yocto
Posts: 98
Original Poster
Rep:
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I added hdmi_group:1=1
The TFT is 3.5" so 320x480 px.
Now the situation is shown in the attached picture: on the HDMI screen (my TV) I see the raspberry logo with the message: "polkit service"
The TFT is showing the desktop screen.
It seems that also the HDMI is working but not as extended screen
What could I do?
Thanks
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11-27-2020, 05:41 AM
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#7
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LQ Guru
Registered: Jan 2006
Location: Ireland
Distribution: Slackware, Slarm64 & Android
Posts: 17,278
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I think you could write yourself a config in /etc/X11/xorg.conf.d/20-video.conf. Man xorg.conf has the details, and you'll find examples online. Have 2 Monitor sections, describe both Monitors, and X will use them if they are there, and ignore them if they are not.
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11-27-2020, 05:44 AM
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#8
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LQ Guru
Registered: Sep 2011
Location: Upper Hale, Surrey/Hants Border, UK
Distribution: One main distro, & some smaller ones casually.
Posts: 5,781
Rep: 
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The only other thing I can think of is this topic - https://www.instructables.com/How-to...tors-in-linux/
(Not sure if it will help or not, but worth a look probably.)
Failing that, I'm afraid I'm out of ideas; as I said, mine just worked.
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11-27-2020, 01:38 PM
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#9
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LQ Guru
Registered: Jan 2006
Location: Ireland
Distribution: Slackware, Slarm64 & Android
Posts: 17,278
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Afaik, default linux gives same screen left + right, but should set modes correctly
There's default configs somewhere weird like /usr/lib/X11/ or /usr/share/X11/xorg.conf.d/ where my box has them. They are just defaults but X reads them but /etc/X11/xorg.conf.d/ overwrites them
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