I've screwed up something in my math above...sorry. Reading up on pixel clocks.
On Tuesday, January 19, 2021 at 9:28:34 PM UTC-5 Matt Parnell wrote: > 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/d43c634b-8d51-4287-b959-f275898a4986n%40googlegroups.com.
