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

[hiro <23hiro@gmail.com>]

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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