Pi Display Puzzle

I’ve had my Pi about a month or so and have had no problems with the display until now. I used the same display settings that I had used previously with Virtual Acorn. I chose the AKF92 Monitor and the 1280×1024×16M mode. It looked good and never needed changed.

This weekend I got a bit experimental with the Pi. I wrote one of the Pi Linux distributions (Raspbmc) to an SD card in order to play with the media centre, which was really quite good. I tried it through the compoosite video and it looked good on the television too. Then I tried RISC OS on the tele just for the hell of it. It was usable but not great on the eyes.

After going back to normal (RISC OS on the Monitor) I have had display trouble. Unless I use the built in Pi MDF, the monitor only uses about half the screen, centred in the middle. Even with this MDF at 1240×720 there is still a half inch of space around the desktop.

When the Pi is booting the first splash screen uses full screen and then goes to half size when running the boot sequence. I’ve tried raspbmc on the monitor and it looks fine with a full display, so the problem does not seem to be physical. I have even tried writing a fresh SD card with RC6 and still have the same problem. The Monitor is a Viewsonic VG930m.

If anyone has any idea what I have done, I would appreciate help to put it right.

Cheers,
Rebecca.

Just use a MDF with the right resolutions, the frequencies don’t matter on a Raspberry Pi.

Changing resolutions / MDFs make no difference. It all just scales inside the half width display.

Can you post the config.txt of the working Raspbmc and the faulty RISC OS?

Hi Jess,

RISC OS
-——
fake_vsync_isr=1
gpu_mem=64
init_emmc_clock=100000000
kernel=RISCOS.IMG
hdmi_group=2
hdmi_mode=35

Raspbmc
-——-
arm_freq=800
force_turbo=1
disable_overscan=0
gpu_mem_256=128
gpu_mem_512=256

I’m at a loss. It worked fine before.

Edit: I added the two last entries in the RISC OS one. It made no difference.

Cheers,
Rebecca.

You have 2 problems

• The half inch of space around the desktop has something to do with “disable_overscan=” in your config.txt
• half the screen, centred in the middle, should be solved with a MDF with the right resolutions

Thanks for your suggestions Wouter. disable_overscan is not in the RISC OS config.txt though. I’ll have a mess later with MDFs.

Cheers.

Well, adding disable_overscan=1 has cured the half inch at the top and bottom. The original problem remains though, with the exception of the built in mdf. That one fills the screen at 1280×720, but looks vertically stretched.

These two are telling the Pi to override the automatic detection and use 1280 × 1024:

hdmi_group=2
hdmi_mode=35

If it works OK under Raspbmc without them, then I would think it is not needed.

have you tried using the raspbmc config.txt?

I have re-written the RC6 image to the SD card, so all the settings are ‘factory’ The default high resoltion screen fills the display fine, so it seems like the hardware is OK. As soon as I try an MDF and select 1280×1024 resolution the screen squashes up with a large gap at each side. Its puzzling because most MDfs and modes scaled to the screen before.

I have no knowledge of how HDMI works, but was wondering… Is it possible that my cheap HDMI – DVI lead has failed in some way but afreature of the Linux drivers is compensating?

Will try the Raspbmc config.txt next.

Cheers.

No difference with trying the other config.txt

Maybe 1920×1080 will grow on me :)

No difference with trying the other config.txt

Maybe 1920×1080 will grow on me :)

I have no knowledge of how HDMI works, but was wondering… Is it possible that my cheap HDMI – DVI lead has failed in some way but afreature of the Linux drivers is compensating?

That was exactly what I was thinking.

What is the native resolution of the display?

I think my HDMI > DVI lead is a cheap one as well but I have altered the config.txt to tell it which resolution to use (1080p, none of the other 1080 modes work). Try using the hdmi_mode=35 (or 36/37) without the hdmi_group=2 line (comment it out using #).

Thanks Peter for the suggestions. Those values made no difference though.

Something is causing the Pi to detect your 1280×1024 monitor as a 1280×720 monitor, I assume, if it’s looking vertically stretched, and 1280×1024 is looking horizontally squished.

Try exactly these steps:

Add the following contents into config.txt, removing any conflicting lines, but leaving everything else alone:

disable_overscan=1
hdmi_ignore_edid=0xa5000080
hdmi_ignore_cec=1
hdmi_drive=1
hdmi_group=2
hdmi_mode=35
framebuffer_width=1280
framebuffer_height=1024
config_hdmi_boost=4

Once you’ve done this (about every compatibility command related to video I can find in there), boot into RISC OS Pi. Go into Configure, then Screen, select Generic monitor, 1280×1024, 60 Hz, 16M colors. Set the mode, see what happens.

Thank you Eric, that has sorted the problem out. It is working fine now and continued to do so after a reboot. Thank you also to everyone who tried to help earlier.

I have backed up a copy of config.txt

Cheers,
Becky.

I’m guessing your monitor has a bad EDID, that Linux is somehow treating differently than RISC OS is (there’s some stuff in Raspbian that lets Linux change things at the VideoCore level that, AFAIK, RISC OS can’t change right now). So, basically, all of those settings are to force it to ignore the EDID, and then be very sure that all of the right settings are in place to make up for the EDID being missing.

Thanks Eric. You are probably right about the monitor. It is a ViewSonic, cheap and cheerful.

Cheers,
Rebecca.

I’m guessing your monitor has a bad EDID, that Linux is somehow treating differently than RISC OS is

I may be wrong but I thought start.elf and the GPU detect and set up the GPU for both RISC OS and Linux.

Rebecca: are you using the same start.elf on both cards?

Chris: However, Linux can use tvservice to change the RPi’s GPU settings after boot, whereas AFAIK RISC OS currently needs a reboot.

Hi Chris. I don’t know anything about start.elf or the firmware stuff. I have the current version of Raspbmc and have not touched any of those files. I’m running RISC OS Pi RC6 with an upgraded firmware via !Packman.

Hope that helps.
Cheers,
Becky.

Rebecca: The problem could be different firmware (start.elf) or other differences. But as you’ve got it sorted we may never know the source of the problem.