Robert, Thank you so much for the quick reply and clarification regarding enabling/disabling outputs. Makes sense.
But I'm still not sure why I can't get 1680 x 1050. I believe the AM335x pixel clock is limited to 126.5 MHz. If I understand how this works, and the relationship is 1:1 (pixels per Hz; color is communicated via parallel bits), 1920 x 1080 x 30 Hz = 124.4 MHz (just below the limit). So, it's clear why we can't do 1080p at 60 Hz. That said, 1680 x 1050 x 60 Hz = 105.8 MHz. This *should* be below the limit, right? What am I missing? BTW - While I didn't have success with it in prior iterations, I just tried "video=HDMI-A-1:1920x1080@30e". I didn't get video, but I did get my monitor indicating "Input Signal Out of Range" - which tells me the BBB is doing its job, my monitor just can't handle 30 Hz (not unexpected). I'm not sure what's different this time around; I swear in the past it would just revert to 1280x1024 when I tried that setting, but maybe I'm not remembering some detail. On Tuesday, January 19, 2021 at 8:55:12 PM UTC-5 RobertCNelson wrote: > On Tue, Jan 19, 2021 at 7:16 PM Matt Parnell <[email protected]> wrote: > > > > I've been working for some time on trying to achieve the highest > resolution possible for a BeagleBone Black system I'm setting up as a > dashboard running Chronograf. > > > > I've tried multiple operating systems and builds (including a brief > stint with FreeBSD), but what I'm using now is a Debian 10.7 console build > (4.19.94-ti-r57) downloaded from Robert Nelson's server > (BBB-blank-debian-10.7-console-armhf-2021-01-11-1gb.img.xz). FWIW, none of > the versions I've tried (including those with LXQT) seem to make much > difference with regard to the issue I'm facing... > > > > The BBB seems to really want to default to 1280x1024x60. I can't get the > resolution I want - which is 1680x1050 (I really want 1920x1080, but I > suspect my monitor won't support 24 or 30 Hz). > > > > I've been able to get 1440x900x60 by adding > "video=HDMI-A-1:1440x900@60e" to "cmdline" in uEnv.txt. Unfortunately, > setting this to 1680x1050x60e seems to cause the resolution to revert to > 1280x1024. BTW - what does the "e" suffix do? I've tried with and without, > and haven't figured out what its significance is. > > > > I don't see 1680x1050 in the list on > https://elinux.org/Beagleboard:BeagleBoneBlack_HDMI#Supported_Resolutions, > but from I've read it should work? > > > > I read somewhere that resolutions/bandwidth are limited via the audio > channel. So I've also tried disabling HDMI audio (I don't use it) by > un-commenting "disable_uboot_overlay_audio=1". > > > > My monitor, by the way, is an older HP Compaq LA2405x. I have confirmed > that it supports 1680x1050 at 60 Hz. It is connected to the BBB via a mini > HDMI to HDMI cable, then an HDMI to DVI cable. I'm nearly certain that the > monitor isn't the issue, as it will report on-screen if an input > resolution/frequency is out of range (and I'm not getting that). > > > > I've also tried setting the resolution for my Xorg session, but from > what I can tell, the driver (fbdev?) doesn't permit changing resolution. > When I run xrandr, it seems to indicate that my minimum and maximum > resolution is equal to the resolution I've already forced via uEnv.txt. > > > > Forgive me if I've missed important details or this is a bit scattered. > Most of this effort occurred over the weekend (before I had access to this > group), so I'm trying to re-visit the key steps I took (ignoring many that > appeared to have no impact). > > I don't remember where this is explained in the u-boot/kernel code. > But the BeagleBone Black's AM335x just doesn't have enough memory > bandwidth to fully support "large" screen sizes.. > > This is why 1080p maxes out at 30 fps, or 24 fps when audio is also > involved.. > > The 'e' is documented here: > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/fb/modedb.rst?h=v5.11-rc4 > > "DRM drivers also add options to enable or disable outputs: > > 'e' will force the display to be enabled, i.e. it will override the > detection > if a display is connected. 'D' will force the display to be enabled and use > digital output. This is useful for outputs that have both analog and > digital > signals (e.g. HDMI and DVI-I). For other outputs it behaves like 'e'. If > 'd' > is specified the output is disabled."... > > Regards, > > -- > Robert Nelson > https://rcn-ee.com/ > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/dc233746-9050-41da-a12c-092393fbff93n%40googlegroups.com.
