[9fans] No signal on some monitors with Raspberry Pi 400

[9fans] No signal on some monitors with Raspberry Pi 400

[Kent R. Spillner]

Howdy-

I recently bought a Raspberry Pi 400 and installed Richard Miller's 9pi img
(https://9p.io/sources/contrib/miller/9pi.img.gz) onto a microSD card via
Raspberry Pi's Imaging tool.

Everything works fine and I'm really enjoying learning Plan 9, however some monitors
don't detect any signal.  That is, if I plug into a ~10 year old Vizio television
everything works fine at a reasonable resolution (1280x1024?  I haven't yet figured
out which utility to use to query display properties), but if I plug it into a Dell
S2817Q the monitor says "No signal detected."  I've successfully plugged the Pi back
and forth between the two displays several times and the behavior is consistent:
everything works fine on the smaller, older Vizio tv, but "no signal" on the Dell.

Has anyone else experienced anything like this?  Any suggestions for things to try?

I would prefer using the Dell monitor to the Vizio tv, but I'm not concerned about
the resolution.  That is, I would happily prefer running Plan 9 on the Pi at 640x480
on the Dell rather than the higher resolution on the Vizio.  (Ideally, of course, I
would like to run at the highest resolution possible on the Dell, but for the time
being I'd just be happy with anything working on the Dell)

Thank you in advance!



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Re: [9fans] No signal on some monitors with Raspberry Pi 400

[Richard Miller]

> That is, if I plug into a ~10 year old Vizio television
> everything works fine at a reasonable resolution (1280x1024?  I haven't yet figured
> out which utility to use to query display properties)

Here's a simple way:

term% echo `{dd -if /dev/screen -bs 64 -count 1}

> , but if I plug it into a Dell
> S2817Q the monitor says "No signal detected."

That's a 4k monitor, I think. The native resolution is probably too big
to fit in the virtual area allowed for the kernel frame buffer. (Lack of
foresight - monitors were smaller when 9pi was first done.)

I'll see about fixing that soon. Meanwhile, you should be able to use
hdmi_group and hdmi_mode settings in config.txt to request a lower resolution.
Or add something like "vgasize=1600x1200x16" to the command line in cmdline.txt -
either method should work.


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Re: [9fans] No signal on some monitors with Raspberry Pi 400

[Bakul Shah]

On Mar 10, 2021, at 8:53 AM, Richard Miller <9fans@hamnavoe.com> wrote:
>> That is, if I plug into a ~10 year old Vizio television
>> everything works fine at a reasonable resolution (1280x1024?  I haven't yet figured
>> out which utility to use to query display properties)
> 
> Here's a simple way:
> 
> term% echo `{dd -if /dev/screen -bs 64 -count 1}
> 
>> , but if I plug it into a Dell
>> S2817Q the monitor says "No signal detected."
> 
> That's a 4k monitor, I think. The native resolution is probably too big
> to fit in the virtual area allowed for the kernel frame buffer. (Lack of
> foresight - monitors were smaller when 9pi was first done.)
> 
> I'll see about fixing that soon. Meanwhile, you should be able to use
> hdmi_group and hdmi_mode settings in config.txt to request a lower resolution.
> Or add something like "vgasize=1600x1200x16" to the command line in cmdline.txt -
> either method should work.

Not sure how things are different in pi4+pi9 but I was able to get 4K@20Hz
under plan9 back in 2014 on the original pi. Not sure I can find that
SDcard now but the settings were based on what I gleaned from this thread: 
https://www.raspberrypi.org/forums/viewtopic.php?t=79330
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Re: [9fans] No signal on some monitors with Raspberry Pi 400

[hiro]

i even get 4k@60hz here on a rpi4 on 9front, but there was a lot of
interference with bluetooth, wifi and usb3, it might be you need an
extra strong signal, did you try with a short cable that has a high
bandwidth?

On 3/10/21, Bakul Shah <bakul@iitbombay.org> wrote:
> On Mar 10, 2021, at 8:53 AM, Richard Miller <9fans@hamnavoe.com> wrote:
>>> That is, if I plug into a ~10 year old Vizio television
>>> everything works fine at a reasonable resolution (1280x1024?  I haven't
>>> yet figured
>>> out which utility to use to query display properties)
>>
>> Here's a simple way:
>>
>> term% echo `{dd -if /dev/screen -bs 64 -count 1}
>>
>>> , but if I plug it into a Dell
>>> S2817Q the monitor says "No signal detected."
>>
>> That's a 4k monitor, I think. The native resolution is probably too big
>> to fit in the virtual area allowed for the kernel frame buffer. (Lack of
>> foresight - monitors were smaller when 9pi was first done.)
>>
>> I'll see about fixing that soon. Meanwhile, you should be able to use
>> hdmi_group and hdmi_mode settings in config.txt to request a lower
>> resolution.
>> Or add something like "vgasize=1600x1200x16" to the command line in
>> cmdline.txt -
>> either method should work.
> 
> Not sure how things are different in pi4+pi9 but I was able to get 4K@20Hz
> under plan9 back in 2014 on the original pi. Not sure I can find that
> SDcard now but the settings were based on what I gleaned from this thread:
> https://www.raspberrypi.org/forums/viewtopic.php?t=79330

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