7" 800x480 TFT HDMI Wrong Display Resolution Rpi4B

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scottmorgan
 
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7" 800x480 TFT HDMI Wrong Display Resolution Rpi4B

Post by scottmorgan »

I loaded the latest 2021-03-04-raspios-buster-armhf-lite onto a Raspberry Pi 4B and when I edit /boot/config.txt per the instructions for the Adafruit 7" 800x480 TFT HDMI Backpack the display still only comes up with a 640x480 resolution.

When I use "fbset" it shows this:

mode "640x480"
geometry 640 480 640 480 16
timings 0 0 0 0 0 0 0 0
rgba 5/11,6/5,5/0,0/0
end mode

The problem may be due to the vc4-fkms-3d?

The file /proc/cmdline shows that the 640x480 resolution is being selected by the kernel. Why?

How do I change the display resolution to "800x480"?

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adafruit_support_mike
 
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Re: 7" 800x480 TFT HDMI Wrong Display Resolution Rpi4B

Post by adafruit_support_mike »

Post your whole /boot.config.txt file between CODE tags please.

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scottmorgan
 
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Re: 7" 800x480 TFT HDMI Wrong Display Resolution Rpi4B

Post by scottmorgan »

This is my config.txt

Code: Select all

# 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=800
#framebuffer_height=480

# uncomment if hdmi display is not detected and composite is being output
#hdmi_force_hotplug=1

# uncomment to force a specific HDMI mode (this will force VGA)
hdmi_group=2
hdmi_mode=87
hdmi_cvt=800 480 60 6 0 0 0
hdmi_drive=1

max_usb_current=1

# 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 infrared communication.
#dtoverlay=gpio-ir,gpio_pin=17
#dtoverlay=gpio-ir-tx,gpio_pin=18

# 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

[rtc]
dtoverlay=i2c-rtc,ds3231

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scottmorgan
 
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Re: 7" 800x480 TFT HDMI Wrong Display Resolution Rpi4B

Post by scottmorgan »

Just an observation:
If I add "disable_fw_kms_setup=1" to config.txt then the display comes up 800x480 but then when I try to run a Python 3 app that uses Kivy then nothing is displayed when I run one of their example apps. So my assumption is that I want to use "KMS" but whatever KMS is doing is causing the display resolution to change.

If I comment out this line in config.txt then the display doesn't work properly at all and only the rainbow color pattern is displayed after boot:
#dtoverlay=vc4-fkms-v3d

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adafruit_support_mike
 
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Re: 7" 800x480 TFT HDMI Wrong Display Resolution Rpi4B

Post by adafruit_support_mike »

scottmorgan wrote:If I add "disable_fw_kms_setup=1" to config.txt then the display comes up 800x480 but then when I try to run a Python 3 app that uses Kivy then nothing is displayed when I run one of their example apps.
KMS is the Linux video mode control system. The fact that it's choosing a resolution of 640x480 means it doesn't think the display can handle the 800x480 resolution specified in the file.

That's probably an EDID issue.

HDMI video sources have the option to ask the display what modes it supports, and to choose the one it thinks is best. The information the display provides is called its Extended Display Identification Data, or EDID.

HDMI sources aren't required to ask for the EDID, or to use anything in it if they do, so displays may or may not provide any information in response to an EDID request.

Try adding the line:

Code: Select all

hdmi_ignore_edid=0xa5000080
That tells the OS to use the display specs given in the config file rather than pay attention to anything in the EDID.

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scottmorgan
 
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Re: 7" 800x480 TFT HDMI Wrong Display Resolution Rpi4B

Post by scottmorgan »

When I add that line and restart I still see that rainbow pattern on the screen at startup for about for about 10 seconds. Is that a sign of a problem?

When I use "fbset" I still see that the mode is "640x480". Any other ideas as to how to force the display resolution to be 800x480? Are you able to try this display with a Raspberry Pi 4B and the the version of Raspberry Pi OS Lite released on 2021-03-04 which has Linux kernel 5.10.17?

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scottmorgan
 
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Re: 7" 800x480 TFT HDMI Wrong Display Resolution Rpi4B

Post by scottmorgan »

Has anyone figured out how to properly configure this display for use with a Raspberry Pi 4B?

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adafruit_support_mike
 
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Re: 7" 800x480 TFT HDMI Wrong Display Resolution Rpi4B

Post by adafruit_support_mike »

I'm afraid I haven't found any way to solve the problem. You might want to check with the folks over in the RasPi Foundation forums:

https://www.raspberrypi.org/forums/

They know the video system and the latest changes to the OS better than we do.

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scottmorgan
 
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Re: 7" 800x480 TFT HDMI Wrong Display Resolution Rpi4B

Post by scottmorgan »

I found something that appears to fix the issue:
"The RPi4B should use the HDMI socket next to the power socket for a single monitor setup."

I had my HDMI cable connected to HDMI 1 and not HDMI 0. After switching the cable to HDMI 0 I am able to get the proper display resolution.

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adafruit_support_mike
 
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Re: 7" 800x480 TFT HDMI Wrong Display Resolution Rpi4B

Post by adafruit_support_mike »

Glad to hear you found a solution, and thanks for posting the follow-up!

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