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High monitor resolutions on Raspberry Pi


TLXOS 4.8.0 / TMS 8.2.0 and later use tvservice to get a list of resolutions your monitor(s) actually support, and present this list in the TMS/Tlxconfig GUI.  Earlier versions provide only a hardcoded list of (low) resolutions, some of which your monitor might not support.

The Raspberry Pi 3 and earlier function very differently to the Pi 4 and later.  The Pi 4 uses RANDR-based resolution selection just like x86 platforms do, whereas Pi 3 and earlier still use [Pi-]firmware-based resolution selection that requires a reboot to activate and will not support 4K resolutions without manual intervention.

To get a 4K resolution on a Pi 3, you can edit /boot/config.txt manually to enter the necessary hdmi_cvt or hdmi_timings commands (see any number of forum posts such as  If using TLXOS 4.8.0 or later, the custom mode number 87 will then appear in your pick list.  If using an earlier TLXOS release, our scripting will keep resetting hdmi_mode to whatever resolution you specified in TMS or Tlxconfig, which will interfere with what you are trying to achieve, so you'll have to SSH to your device as root (see the separate knowledgebase article on this) and edit /etc/init.d/tlxinit also.

Unless you have NOOBS (which has a built-in config.txt editor), to edit /boot/config.txt you will have to SSH to the device as root (see the separate knowledgebase article on SSH access) and then run "mount -ro remount,rw /boot" followed by "nano /boot/config.txt" or similar.

The easiest thing to do is to arbitrarily pick one of the resolutions in TMS' list and change the mode number assignment in the lookup_rpi_modenum() function in /etc/init.d/tlxinit such that it corresponds to mode number 87 instead. Selecting that resolution in TMS will then give you your custom resolution (2560x1080 or whatever) instead. Reboot the device after making this change to ensure that it gets saved to flash.

Please note that the Pi's hardware cursor implementation (which is essential for Citrix HDX when using H.264 hardware acceleration) is subject to a 1920x1080 hardware decoding overlay maximum resolution limit, and will cause problems if you attempt to operate your Pi 3 display at higher resolutions.  If you are using a high resolution in HDX or Web mode, you must set the HDX submode option to something other than "H.264" to stop TLXOS from trying to turn the hardware cursor on.  If using Horizon mode, you must deselect the H.264 option in the Horizon Client GUI (or, in recent TMS/Tlxconfig releases, use the "BLAST (No H.264)" submode).

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Article details
Article ID: 12
Category: Workarounds for Old Versions
Date added: 2019-05-29 00:59:48
Views: 367

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