5 inch 720x1280 HDMI IPS LCD Display Rasp Pi4 config.txt as second HDMI port

Products & Technology Raspberry Pi
#1

Hello - a bit new to Pi world, but I have a Rasp 4B that I want to hook this display up to using the second HDMI port. In the documentation, there’s the config.txt settings for the 5" display, but I need to ensure these settings are only applied to the 2nd HDMI port as the 1st HDMI port has a 7" display with no special settings required.

Here’s the settings from the documentation for the 5":

force_trubo=1 (by the way, I assume this is a typo and should be ‘force_turbo’- but do I need this for the Raspberry Pi 4B? Why does this need to be enabled for this 5" monitor?)
gpu_freq=300 (again, why does this need to be specified just for this monitor?)
core_freq=400 (again, why does this need to be specified just for this monitor?)
hdmi_pixel_freq_limit=400000000 (again, why does this need to be specified just for this monitor?)
hdmi_drive=2
hdmi_mode=87
disable_overscan=1

5 inch

hdmi_timings= 720 0 100 33 100 1280 0 20 2 30 0 0 0 60 0 79000000 0
max_framebuffer_width=1280
max_framebuffer_height=1280
display_rotate=1
framebuffer_width=1280
framebuffer_height=720

So, when hooking this display up to the 2nd HDMI port on the raspberry pi 4B, would these entries change to include the HDMI port ‘:1’ suffix?:

hdmi_pixel_freq_limit:1=400000000
hdmi_drive:1=2
hdmi_mode:1=87
disable_overscan:1=1

5 inch

hdmi_timings:1= 720 0 100 33 100 1280 0 20 2 30 0 0 0 60 0 79000000 0
max_framebuffer_width:1=1280
max_framebuffer_height:1=1280
display_rotate:1=1
framebuffer_width:1=1280
framebuffer_height:1=720

Then if for some reason I wanted for force settings for Seeed’s 7" LCD connected to the first HDMI port, would I use the suffix ‘:0’ in all the similar commands above?

hdmi_pixel_freq_limit:0=400000000
hdmi_drive:0=2
hdmi_mode:0=87
disable_overscan:0=1

7 inch

hdmi_timings:0=720 0 100 24 52 1280 0 10 4 4 0 0 0 60 0 70000000 0
max_framebuffer_width:0=1280
max_framebuffer_height:0=1280
display_rotate:0=3
framebuffer_width:0=1280
framebuffer_height:0=720

Again, I’m kinda assuming these three commands below are not required, but may be? Even if they are, they do not need to be directed or a particular HDMI port or do they?

force_turbo=1
gpu_freq=300
core_freq=400

Thanks!
Joe

#2

So you want to connect two different size monitor with RPi4 at the same time?

#3

Yes correct. The 5" connected to HDMI1, and the 7" connected to HDMI0.

#5

Ok Great, and what problem are you facing while connecting two monitor? Sorry I couldn’t t understand exact problem you are facing from your description!

#6

I need the exact syntax when specifying between HDMI0 and HDMI1 ports within the config.txt file.

So for all HDMI related commands, do I add the ‘:0’ suffix for HDMI0 and ‘:1’ suffix for HDMI1?

So, when connecting the 5" display to HDMI1, would all the following commands have the ‘:1’ suffix added:
hdmi_pixel_freq_limit:1=400000000
hdmi_drive:1=2
hdmi_mode:1=87
disable_overscan:1=1

5 inch

hdmi_timings:1= 720 0 100 33 100 1280 0 20 2 30 0 0 0 60 0 79000000 0
max_framebuffer_width:1=1280
max_framebuffer_height:1=1280
display_rotate:1=1
framebuffer_width:1=1280
framebuffer_height:1=720

Then if connecting some other display to HDMI1 and moving the 5" to HDMI0, would all the suffixes change to ‘:0’ as in the following?

hdmi_pixel_freq_limit:0=400000000
hdmi_drive:0=2
hdmi_mode:0=87
disable_overscan:0=1

5 inch

hdmi_timings:0= 720 0 100 33 100 1280 0 20 2 30 0 0 0 60 0 79000000 0
max_framebuffer_width:0=1280
max_framebuffer_height:0=1280
display_rotate:0=1
framebuffer_width:0=1280
framebuffer_height:0=720

Also, why are the following commands required just for Seeed LCD’s:

force_trubo=1 (by the way, I assume this is a typo and should be ‘force_turbo’- but do I need this for the Raspberry Pi 4B? Why does this need to be enabled for this 5" monitor?)
gpu_freq=300 (again, why does this need to be specified just for this monitor?)
core_freq=400 (again, why does this need to be specified just for this monitor?)
hdmi_pixel_freq_limit=400000000 (again, why does this need to be specified just for this monitor?)

#7

@svojoe
Can you send me a picture of your Raspberry Pi and two screens?

#8

Actaully - I have it figured out! The trick (at least in my situation) was to completely ignore the setup instructions for the 5" display. With a fresh install of Buster for my Pi4B (2020-02-13-raspbian-buster-full), and my 7" display hooked to HDMI0, and 5" Seeed display hooked to HDMI1, I checked ‘Can see black boarders around screen’ on the initial config, completed the initial Pi settings, then rebooted. Then simply used the GUI ‘Preferences->Screen Configuration’ and selected the 5" display, and selected ‘Orientation Right’, applied and rebooted. Screen came up fine. BTW - do not attempt to change resolution in GUI for 5" to 640x480 - for some reason this changed something and even after trying to revert back to 720x1280, the 5" stayed black - even after reboot. Had to do another fresh image to get over that test!

Ideas on why the modifications to config.txt would not work? If not - no big deal as I currently have it running on my Pi4B with no config.txt modifications - just used the GUI settings on the Buster desktop.

Thanks,
Joe

1 Like
#9

Raspberry Pi isn’t fully open source on the GPU display, and we have no way to keep track of what’s really going on.

#10

Of course - I thought I had a fix, but after several successful restarts, black screen again! After about 3 more black screen restarts, I simply changed the orientation on the 5" screen in the GUI Preferences from ‘right’ to ‘normal’ and the screen came up - then rotated back to ‘right’ and continued to work again. I also need to mention I’m having a screen flickering issue with this particular 5" display when I hook it up to any PC (not just the Pi) - but after about 15min, the flickering seems to reduce and eventually goes away.

I’m starting to believe I may have a bad unit where the frequency is just out of spec? It seems after the flickering dies down, subsequent restarts are successful. Ideas?

Also, just out of curiosity, with the latest Buster release for the Pi4, to change any display settings manually, should one not be modifying config.txt and using xrandr? When changing display settings using the desktop GUI Preferences->Screen Preferences, where are those settings saved?

Thanks,
Joe

#11

This screen design at the beginning of Raspberry Pi 4 is not yet available, there may be compatibility issues, perhaps you can test it in RPI3 to make sure the screen is free of problems.

#12

I don’t have a RPI3 available as of yet? Does Seeed have a RPI4 to test with? How do you explain the major flickering on several different PC’s when first powering up - then flickering gradually goes away over time (like within 15min until it stops completely)?

Given my configuration:
RPI4B 4G (running the ‘2020-02-13-raspbian-buster-full’ image)
RPI4 Connector HDMI0: 7" 1024x600 IPS LCD, rotated Left
RPI4 Connector HDMI1: 5" 720x1280 IPS LCD, rotated Right (Seeed SKU 104990442)

I learned several other things today - if the 5" Seeed LCD ever boots up black when the main 7" LCD boots up fine with desktop display, I can just go into terminal, then use xrandr to turn off the HDMI-2 port (5" on the HDMI1 connector), then set back up - it flashes, re-syncs and comes up online.

I use the following commands to bring a black-booted 5" Seeed LCD screen to working again:

xrandr --output HDMI-2 --off
xrandr --output HDMI-2 --mode 720x1280 --rotate right --pos 600x0

I took a video of the flashing screen in ‘slow motion’ on iphone and will email to support. Normal video mode on iphone could not capture flashing issue. Hopefully Seeed can send me a new display as no matter what I use to drive the LCD (desktops, laptops, RPI4), it always flashes for like 15min then stops flashing…

Thanks,
Joe

#13

If there is a real problem, I’m sure our after-sales department will be able to help you out very well.