MichaIng
Posts: 5
Joined: Sun Aug 04, 2019 5:56 pm

Clarification about config.txt settings on RPi4

Tue Aug 13, 2019 9:59 pm

Hey guys, I have some questions about how certain config.txt settings work on RPi4 or new settings, introduces with RPi4, have effects on prior RPi models:
  1. With RPi4 the new setting enable_tvout has been introduced since composite video output is disabled by default on RPi4 as of performance reasons. Does this settings have any effect on prior RPi models, thus can composite output be disabled there via enable_tvout=0?
  2. There is an undocumented settings available that allowed to disable composite video on prior RPi models as well: hdmi_ignore_composite. AFAIK in combination with hdmi_ignore_hotplug this allows to disable the whole video pipeline and has thus the same effect as tvservice -o, just from early boot, not recoverable without reboot: https://github.com/raspberrypi/userland/issues/447
    So the question is now if this old setting is obsolete, or if the one has an effect on RPi4 only while the other one affects prior RPi models only. Or do both handle things differently, so it could make sense to set both to have most video features disabled, thus most power saved on headless systems?
  3. On earlier RPi models there were gpu_mem_256/512/1024 to set GPU memory share for models with this amount of memory only. AFAIK the gpu_mem value borders for all RPi4 models (1G/2G/4G) is the same as for prior 1G models, thus is gpu_mem_1024 as well effective on all RPi4 models, or only the 1G one, or are there _2048/4096 settings available now, or must gpu_mem=XXX be used? Too many question in one sentence, sorry :D.
  4. Last but not least, I recognised that vcgencmd get_config sdram_freq always reports 0 on RPi4. The default according to docs is 3200. Reading through some overclocking threads here, no one ever sets this on RPi4. Is the sdram freq simply hardcoded on RPi4?
Probably someone has some insights about this, as the documentation lacks further information for now. Otherwise I would forward these questions to: https://github.com/raspberrypi/firmware/issues

Best regards,
Micha


trejan
Posts: 1112
Joined: Tue Jul 02, 2019 2:28 pm

Re: Clarification about config.txt settings on RPi4

Wed Aug 14, 2019 3:59 pm

MichaIng wrote:
Tue Aug 13, 2019 9:59 pm
With RPi4 the new setting enable_tvout has been introduced since composite video output is disabled by default on RPi4 as of performance reasons. Does this settings have any effect on prior RPi models, thus can composite output be disabled there via enable_tvout=0?
enable_tvout is only recognised by the RPi 4 firmware. It does nothing on the previous RPi boards.
MichaIng wrote:
Tue Aug 13, 2019 9:59 pm
There is an undocumented settings available that allowed to disable composite video on prior RPi models as well: hdmi_ignore_composite. AFAIK in combination with hdmi_ignore_hotplug this allows to disable the whole video pipeline and has thus the same effect as tvservice -o, just from early boot, not recoverable without reboot: https://github.com/raspberrypi/userland/issues/447
hdmi_ignore_composite was removed from the firmware when the Pi 4 support was added. It isn't a valid option in the latest firmware for any RPi board.
MichaIng wrote:
Tue Aug 13, 2019 9:59 pm
Last but not least, I recognised that vcgencmd get_config sdram_freq always reports 0 on RPi4. The default according to docs is 3200. Reading through some overclocking threads here, no one ever sets this on RPi4. Is the sdram freq simply hardcoded on RPi4?
Sort of. Read https://www.raspberrypi.org/forums/view ... 4#p1501414

MichaIng
Posts: 5
Joined: Sun Aug 04, 2019 5:56 pm

Re: Clarification about config.txt settings on RPi4

Thu Aug 22, 2019 7:18 am

drgeoff wrote: A read of https://www.raspberrypi.org/forums/view ... 8&t=247820 might answer your Q3.
Many thanks. This thread does not cover my question, but some other general questions about RPi4 and GPU memory. Also I found the open PR to update the section of the docs and added suggestion to add the info that answers my question: https://github.com/raspberrypi/documentation/pull/1240
trejan wrote: enable_tvout is only recognised by the RPi 4 firmware. It does nothing on the previous RPi boards.
...
hdmi_ignore_composite was removed from the firmware when the Pi 4 support was added. It isn't a valid option in the latest firmware for any RPi board.
Okay, good to know. Yeah I recognised that this has no effect anymore on my RPi2 as well. Framebuffer (/dev/fb0) again is active by default. Even if I disable bcrm fb via dtoverlay in config.txt, some default Linux framebuffer device kicks in instead... So only chance now is to use tvservice -o or disable the brcm framebuffer via overlay on runtime... Or is there any other way to have all GPU/video features, including whole video+framebuffer pipe, disabled directly on boot?
trejan wrote: Sort of. Read https://www.raspberrypi.org/forums/view ... 4#p1501414
Okay, good to know. Indeed that should be added to the docs. Probably I will raise a PR.

mcmanuf
Posts: 44
Joined: Wed Aug 22, 2012 12:29 am

Re: Clarification about config.txt settings on RPi4

Fri Jan 10, 2020 4:24 pm

.. Or is there any other way to have all GPU/video features, including whole video+framebuffer pipe, disabled directly on boot?
Can anyone please answer this question?
Running headless means running headless, ie. no need for hdmi or any ressources to be used for this task.
If even a small amount of memory, or a small amount of ressources can be saved, so be it.

Why is it so difficult to find out about this issue.

I have read in github, kernel updates etc..
And clearly OP has the same question.

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 24912
Joined: Sat Jul 30, 2011 7:41 pm

Re: Clarification about config.txt settings on RPi4

Fri Jan 10, 2020 5:11 pm

mcmanuf wrote:
Fri Jan 10, 2020 4:24 pm
.. Or is there any other way to have all GPU/video features, including whole video+framebuffer pipe, disabled directly on boot?
Can anyone please answer this question?
Running headless means running headless, ie. no need for hdmi or any ressources to be used for this task.
If even a small amount of memory, or a small amount of ressources can be saved, so be it.

Why is it so difficult to find out about this issue.

I have read in github, kernel updates etc..
And clearly OP has the same question.
If no HDMI is attached, then no HDMI will be running. On the Pi4 you might not get a framebuffer either. You will on earlier devices as it will default to composite.

Run up the Pi, SSH in. Run "vcgencmd dispmanx_list" to see if there are any framebuffers created.

You cannot turn off the GPU completely, the system simply won't work.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed. Here's an example...
“I own the world’s worst thesaurus. Not only is it awful, it’s awful."

bitbasher
Posts: 1
Joined: Tue Jan 21, 2020 9:37 pm

Re: Clarification about config.txt settings on RPi4

Tue Jan 21, 2020 9:50 pm

jamesh wrote:
Fri Jan 10, 2020 5:11 pm
If no HDMI is attached, then no HDMI will be running. On the Pi4 you might not get a framebuffer either. You will on earlier devices as it will default to composite.
Run up the Pi, SSH in. Run "vcgencmd dispmanx_list" to see if there are any framebuffers created.

Running recent pi-lite image on a Pi Zero W, if I have no HDMI connected, running tvservice -s returns:
state 0x40000 [NTSC 4:3], 720x480 @ 60.00Hz, interlaced

Running vcgencmd dispmanx_list returns:
display:3 format:RGB565 transform:0 layer:-127 656x416 src:0,0,656,416 dst:32,32,656,416 cost:363 lbm:0

So it appear that since hdmi_ignore_composite is no longer supported that I can't boot with HDMI powered off unless I explicitly state tvservice -o in something like rc.local.

For low-power headless situations, I would really like the HDMI core to be fully OFF unless an HDMI display is connected. If I hardcode a tvservice -o in rc.local it will turn off the HDMI even I have have one connected so I'd need to first check tvservice -s to check for NTSC before forcing the HDMI core off.

Even though hdmi_ignore_composite was considered an "advanced" feature, why was it removed?

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 24912
Joined: Sat Jul 30, 2011 7:41 pm

Re: Clarification about config.txt settings on RPi4

Wed Jan 22, 2020 12:06 am

That is the composite display, not Hdmi. It's expected behaviour.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed. Here's an example...
“I own the world’s worst thesaurus. Not only is it awful, it’s awful."

Return to “Advanced users”