chipace
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Raspberry Pi 4 Dual Monitors

Wed Jul 03, 2019 3:54 pm

Anyone have config.txt settings to get dual monitors working? I am using 2 Dell 24 inch monitors and using DVI to HDMI cables to connect to both.
Presently I can only get one monitor working when plugged into hdmi0. I have played with turning the monitors on quickly right before I power the RPi4, but that does not seem like a good long term solution (and it didn't work).
Each monitor works just fine by itself in hdmi0 (both cables work). Monitor resolutions are the standard 1920x1200.

jamesh
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Re: Raspberry Pi 4 Dual Monitors

Wed Jul 03, 2019 3:59 pm

Hmm, that should work OK out of the box. I'm using a very similar Dell monitor with no problem when combined with another DELL (4k) on the HDMI 0.

With both plugged in what does the following return?

tvservice -l
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6by9
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Re: Raspberry Pi 4 Dual Monitors

Wed Jul 03, 2019 4:02 pm

With Raspbian there should be nothing special required. The Pi will probe the monitors and run with what it finds.
Monitors generally reply with their EDID whether they are on or sleeping. Some even reply when turned off (HDMI provides a low power supply for this purpose).

If you boot the Pi with both monitors connected, then "tvservice -s -v 2" and "tvservice -s -v 7" will report the status of the two HDMI ports. Please report back what it says.

If they are identical monitors, then you could try forcing the mode.

Code: Select all

tvservice -d edid.dat
sudo cp edid.dat /boot/
Edit /boot/config.txt and add

Code: Select all

hdmi_edid_file:1=1
hdmi_edid_filename:1=edid.dat
hdmi_force_hotplug:1=1
Software Engineer at Raspberry Pi Trading. Views expressed are still personal views.
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chipace
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Re: Raspberry Pi 4 Dual Monitors

Wed Jul 03, 2019 4:31 pm

I am using the 2GB RPi4, and I see the 4 raspberries on one monitor (connected to hdmi0) and sometimes the rainbow colors on the other monitor (connected to hdmi1). The monitor on hdmi0 hangs with a blank screen and then monitor on hdmi1 goes into power saving. It looks like it is hanging during boot. I am using 192MB for GPU memory (not the default setting). SPI and I2C buses enabled. Everything else is stock configuration.

My 1GB RPi4 arrives in a few hours so I will try the same sd card on that board.

chipace
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Re: Raspberry Pi 4 Dual Monitors

Wed Jul 03, 2019 4:39 pm

Edit /boot/config.txt and add

hdmi_edid_file:1=1
hdmi_edid_filename:1=edid.dat
hdmi_force_hotplug:1=1
This worked for me!! I now have the issue where one screen is proper resolution (1920x1200 59.95Hz) and the other one has a max available resolution of 1024x768 60Hz. I am using the "Screen Configuration" under the Perferences menu.

chipace
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Re: Raspberry Pi 4 Dual Monitors

Wed Jul 03, 2019 5:26 pm

Here are a few more details.
(1) It only worked when there was no /boot/edid.dat file
(2) It hangs at boot when there is a /boot/edid.dat file
(3) Single monitor operation hangs with these config.txt settings

I am getting the monitor model numbers by using the monitor's button menu (both show the model number of DELL U2412M). Identical as far as I can tell. I switched monitor cables and I see one monitor at 1920x1200 59Hz and the other at 1024x768 60Hz. Whatever is plugged into the second micro-hdmi port is coming up with the lower resolution.

I will post again when I try this on the 1GB RPi4.

chipace
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Re: Raspberry Pi 4 Dual Monitors

Wed Jul 03, 2019 6:36 pm

Removed previous config.txt changes and tried with heterogeneous monitors (DELL U2412M and DELL 1905FP). No problems booting, but the second display was blank, but did report settings from "tvservice -s -v 7".

Is there a config file for the monitor configuration that I can clear (delete) so that previous configurations do not interfere when I connect different monitors?

kotovasii
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Re: Raspberry Pi 4 Dual Monitors

Wed Jul 03, 2019 7:00 pm

chipace wrote:
Wed Jul 03, 2019 6:36 pm
Removed previous config.txt changes and tried with heterogeneous monitors (DELL U2412M and DELL 1905FP). No problems booting, but the second display was blank, but did report settings from "tvservice -s -v 7".

Is there a config file for the monitor configuration that I can clear (delete) so that previous configurations do not interfere when I connect different monitors?
I have been having many issues with Pi4 4GB RAM when changing the GPU_MEMORY setting in the raspi-config and thus the config.txt file. I find that the User Guide is very poor in relation to GPU memory and does not relate clearly how to set it up and what settings to choose. I found that with any settings the quality of resolution is rather "choppy" as if I were back in windows 3.1 /DOS era... I look at my Mac here and Win10 desktops where graphics is smooth, Pi4 display is almost pixelated... I found that changing to 512 MB GPU stops black screen (3 berries or rainbow then hang). The resolution is still awful, despite a good Dell monitor

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Re: Raspberry Pi 4 Dual Monitors

Wed Jul 03, 2019 7:17 pm

At a guess it can't read the edid of the second monitor, in which case drm adds the standard dmt modes up to 1024x768. Hdmi_force_hotplug should ignore the hot plug line and hdmi_edid_file should provide the missing edid.
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PeterO
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Re: Raspberry Pi 4 Dual Monitors

Wed Jul 03, 2019 7:19 pm

6by9 wrote:
Wed Jul 03, 2019 4:02 pm
With Raspbian there should be nothing special required. The Pi will probe the monitors and run with what it finds.
Monitors generally reply with their EDID whether they are on or sleeping. Some even reply when turned off (HDMI provides a low power supply for this purpose).
My experience is that does not happen to the monitor plugged into HDMI-1

Unless it is fully on (i.e. not gone to sleep due to the lack of an input signal) the PI will not wake it up, and then often fails to configure HDMI-0 as well.

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aBUGSworstnightmare
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Re: Raspberry Pi 4 Dual Monitors

Wed Jul 03, 2019 7:25 pm

Post the results of below listed commands

Code: Select all

tvservice -l
tvservice -n
tvservice -m DMT
something is going wrong at your end as the RPi desktop is not 'pixelated'. I've tried running a 31.5in UHD (4k resolution) today and the display looks awsome!

jamesh
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Re: Raspberry Pi 4 Dual Monitors

Wed Jul 03, 2019 8:06 pm

kotovasii wrote:
Wed Jul 03, 2019 7:00 pm
chipace wrote:
Wed Jul 03, 2019 6:36 pm
Removed previous config.txt changes and tried with heterogeneous monitors (DELL U2412M and DELL 1905FP). No problems booting, but the second display was blank, but did report settings from "tvservice -s -v 7".

Is there a config file for the monitor configuration that I can clear (delete) so that previous configurations do not interfere when I connect different monitors?
I have been having many issues with Pi4 4GB RAM when changing the GPU_MEMORY setting in the raspi-config and thus the config.txt file. I find that the User Guide is very poor in relation to GPU memory and does not relate clearly how to set it up and what settings to choose. I found that with any settings the quality of resolution is rather "choppy" as if I were back in windows 3.1 /DOS era... I look at my Mac here and Win10 desktops where graphics is smooth, Pi4 display is almost pixelated... I found that changing to 512 MB GPU stops black screen (3 berries or rainbow then hang). The resolution is still awful, despite a good Dell monitor
You should not need to change any memory settings at all - just leave them alone. They do not affect the display at all.

In fact to get the max resolution a monitor exposes, you should just need to plug it in. It should automatically go up to 4kp30. If you specifically want 4kp60 then you can set the hdmi_enable_4k=1 in config.txt.

Note, 4kp60 will only work in HDMI port 0.

That said, there do appear to be some issues with some monitors, and perhaps some Pi4's, which we have been looking in to. For those who are able to try it without worrying about a broken install, rpi-update may have some changes in that will help.

If after all that there are still issues, something weird is going on we need to figure out. Often this is the monitor failing to supply a EDID, or a valid EDID. They should be able to supply something sane even when of, but sometimes they don't work as hoped.
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chipace
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Re: Raspberry Pi 4 Dual Monitors

Wed Jul 03, 2019 9:51 pm

Thanks PeterO.
Something is up with hdmi1. For now I will just use hdmi0.

chipace
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Re: Raspberry Pi 4 Dual Monitors

Wed Jul 03, 2019 10:25 pm

A google search about Buster edid override revealed a known bug:

https://bugs.debian.org/cgi-bin/bugrepo ... bug=906180

I don't know if this applies to my case, but I have not been able to do an edid override from a file also.

Prince Hal
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Re: Raspberry Pi 4 Dual Monitors

Thu Jul 04, 2019 3:22 am

I'm also having trouble running a combination of HDMI and DVI monitors. Each works fine in the HDMI0 port (I'm using a DVI->HDMI cable for one and HDMI->HDMI for the other). But when I plug both in, the HDMI1 port only puts the rainbow colored splash screen on the monitor.

Here's the relevant section of config.txt:

# uncomment to force a specific HDMI mode (this will force VGA) [note: this is for the HDMI monitor, which is actually an old iMac running in slave mode]
hdmi_group=2
hdmi_mode=87
max_framebuffer_width=2560
max_framebuffer_height=1440
hdmi_pixel_freq_limit=250000000
hdmi_cvt=2560 1440 56 5 0 0 1
hdmi_ignore_edid=0xa5000080
gpu_mem=64

# [this is for the second monitor]
hdmi_group:1=2
hdmi_mode:1=58
# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
hdmi_drive=2



What should I be seeing on the second monitor instead of the rainbow splash screen? Or does it need to be activated to work as an extension of the first screen?

I've tried several different monitors, by the way.

6by9
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Re: Raspberry Pi 4 Dual Monitors

Thu Jul 04, 2019 6:28 am

chipace wrote:
Wed Jul 03, 2019 10:25 pm
A google search about Buster edid override revealed a known bug:

https://bugs.debian.org/cgi-bin/bugrepo ... bug=906180

I don't know if this applies to my case, but I have not been able to do an edid override from a file also.
We are not using that mechanism, so n/a.
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tvjon
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Re: Raspberry Pi 4 Dual Monitors

Thu Jul 04, 2019 8:48 am

I see that arandr has has been updated, along with a firmware fix to re-enable Composite video on RPi3.

So, having installed those, I`ve tried yet again connecting a second HDMI monitor to HDMI1.

Select Screen Configuration.

Both monitors are showing the desktop, but the wrong relative orientation for my present setup.

So, drag the HDMI2 box over to where I need it. Actually, any reason the board physical port names are 0 & 1, but arandr is 1 & 2?

Click the green tick mark to apply, & Pi4 locks up completely, just showing the hourglass.

Power off, repeat twice more. Same result, so give up, power off HDMI 2 screen. Now HDMI1 shows the usual nice fast boot text, but nothing further. Blank screen, no SSH possible.

Repeat twice more...

Next, physically unplug HDMI2 cable.

Reboot, phew, success, back to where I started.

tvservice for both monitors doesn`t look odd in any way.

jamesh
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Re: Raspberry Pi 4 Dual Monitors

Thu Jul 04, 2019 8:57 am

tvjon wrote:
Thu Jul 04, 2019 8:48 am
Actually, any reason the board physical port names are 0 & 1, but arandr is 1 & 2?
The HDMI 0-1 and HDMI1-2 is a PITA, but a consequence of the way that DRM allocates things. We are looking in to what to do about it. One issue is that if you just have one HDMI plugged in to HDMI PORT 1, then its given the label by DRM of HDMI 1, the same as if it were plugged in to HDMI PORT 0!. There doesn't seem to be a way of naming them based on the port they are found on, rather than just an incrementing number.
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tvjon
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Re: Raspberry Pi 4 Dual Monitors

Thu Jul 04, 2019 9:40 am

Thank you for that insight. I imagine a lot of posts exist because their authors are unaware of just how much effort is required to overcome what are sometimes industry self inflicted problems.

BoydLabBuck
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Re: Raspberry Pi 4 Dual Monitors

Sat Jul 06, 2019 2:47 am

I'm having similar problems, using two different displays.

HDMI 0 will work on either display when I swap cables, HDMI 1 will not work on either when swapping cables. Initially the boot would not complete with both displays plugged in, but commenting out dtoverlay resolved that.

masterofslack
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Re: Raspberry Pi 4 Dual Monitors

Sun Jul 07, 2019 5:14 am

Was also having the problems described above. I'm using two identical brand-new LG monitors. Both are model 24MK400H-B.

With both both plugged in, Pi would not complete booting. But either monitor could be used as single display plugged-in to HDMI-0. Just bought these monitors on Friday.

However, I have now turned off "SMART ENERGY SAVING" and "Automatic Standby." Now I have no problem booting with both monitors plugged in, and they seem to work fine.

maddogdave
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Re: Raspberry Pi 4 Dual Monitors

Sun Jul 07, 2019 12:14 pm

I’ve just tested on 2 Samsung 24” TV’s. Clean Raspbian image, 5 days old.
Both worked fine without issues until I tried swapping them via the on screen interface.
OK until reboot, when I then experienced a similar blank screen issue as described above.
Rainbow, 4 Pi’s, a brief flash of the startup screen and then nothing.
Pulling the second monitor cable out and rebooting again was the only way to get a display working.
Dave

masterofslack
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Re: Raspberry Pi 4 Dual Monitors

Sun Jul 07, 2019 12:39 pm

My earlier report of success was premature. The Pi4 had successfully rebooted into dual display a couple of times, but now I'm back to square one.

It's erratic. Even if I turn on both monitors immediately before plugging in the Pi and ensure that both monitors haven't entered power-saving mode, I can't get it to boot. The fact that the Pi refuses to boot at all unless the second monitor is unplugged makes this doubly frustrating.

I have both a 1GB and a 4GB Pi4 and have replicated the issue on both of them.

...If anyone knows of a suitable monitor selling for <$150 in the States, please advise. I suppose I'll have to return this pair.

aBUGSworstnightmare
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Re: Raspberry Pi 4 Dual Monitors

Sun Jul 07, 2019 12:54 pm

just made some test with 2 identical FHD monitors which was successful .

Started with only one monitor connected to HDMI0. Flashed clean Buster, then booted for the first time, skipping the assistant and doing all settings via 'Raspberry Pi Configuration'.
Followed by an update/upgrade I also updated to latest (unofficial) firmware (sudo rpi-update').
When everything was finished I shut-down, connect second monitor and have dual display. Tested a 1GB and a 2GB RPi 4. Now re-started for getting dual display on my CM3L hardware (which failed so far with Buster).

maddogdave
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Re: Raspberry Pi 4 Dual Monitors

Sun Jul 07, 2019 1:01 pm

No point looking for new monitors, it’s clearly a Pi issue that almost certainly can be solved once the foundation have seen this sort of feedback from us early adopters of the Pi4.
Whilst we’ve all used different displays and tried different combinations, the actual issue experienced is the same, or certainly very similar.
When I first changed the settings, rebooting the Pi three times got it working. Then I tried changing some settings and couldn’t get any display with both HDMI connected. Going to a single output got me back to a working system, on one display. Plugging in the second display and rebooting got me an image on my first monitor, but with just one edge of the main display window showing.
I found the on screen interface for setting up the dual monitors rather clunky and not well implemented. Dragging and dropping the displays to swap them wasn’t obvious (to me) until I looked up ThePiHut tutorial, and even then the displays don’t ‘snap’ into place, so swapping 2 boxes around on a screen was a far more difficult task than it should have been.
The more feedback we can give, the quicker this issue will be solved.
Dave

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