PowerBook G4 and Mac mini G4 meet Ultra HD (sort of) and WQUXGA

So I recently picked up an Atlona DP-400 Dual Link DVI to Mini DisplayPort converter very cheaply, and used it to connect my 15in PowerBook5,6 (early 2005 1.67 GHz with dual-link DVI) to my Dell P2415Q monitor.

The good news is that 3840×2160 at 30 Hz works and is displayed properly at first glance. Panther, Tiger and Leopard are really majestic at that resolution, even though the monitor's size (23.8 inches) makes everything very small (I'll say I like it that way, however ).



However, there's framebuffer corruption (i.e. it also shows up on screenshots, not just the monitor itself) going on starting at a width of about 2660 pixels. Windows seemingly disappear when they're dragged across that boundary, and dragging them back reveals that the wallpaper is showing in the parts that were across the boundary. The desktop itself including the menu bar and icons and full-screen applications are not affected, though.

This screenshot illustrates the problem - the right part of the Safari window simply disappears:



2560×1440 at 60 Hz works perfectly. I'll have to see (1) if I get a similar behaviour when running Linux on the PowerBook and (2) if this problem disappears on Mac OS X when using a resolution that's not wide enough to run into this boundary; e.g. 2624×2160 or something like that - UPDATE: no problems at 2656×2160.

I'm fully aware of the fact that the PowerBook's GPU never "supported" resolutions higher than 2560×1600 but it's fun to see how far one can make the old machines go...

 

I've also been thinking about that - the pixel clock for 2560×1600 at 60 Hz is ~270 MHz; for 3840×2160 at 30 Hz it's ~262 MHz. Theoretically, fully exploiting DL-DVI's 330 MHz pixel clock limit should allow a 37 Hz refresh rate. I'll have to look into that.

The monitor has HDMI but since I only have a "crappy" DVI-to-HDMI cable which is single-link, 1920×1080 at 60 Hz is the highest setting which will work out of the box when driven by the PowerBook using this cable. The system actually allows me to select the higher resolutions but since Mac OS X switches to a dual-link signal the monitor only shows a garbled image. What's slightly interesting is that 2048×1152 at 60 Hz is also output as a dual-link signal despite its pixel clock being lower than the single-link limit, which explains why it only works when using the Atlona converter and not when using the single-link connection.

The corruption is the same in Panther, Tiger and Leopard. I have noticed that once the mouse cursor has crossed the "invisible boundary", I can't bring up the right-click menu or click on desktop icons either.

I only own a SLSD, unfortunately but hope to be able to add a DLSD to my collection

 

I apologise for bringing up that thread again but I recently experimented some more with the DP400/P2415Q combo.

So, on the 15in PB with the 128MB 9700 and dual-link DVI running at 3840×2160, framebuffer corruption appears at a width/horizontal res of 2656 pixels, which led me to try a custom mode of 2656×2160 which works perfectly. Right now I'm running this at 43 Hz refresh, for no other reason that the required pixel clock is about 270 MHz, which is known to work for 2560×1600 at 60 Hz. 2656×2160 at 50 Hz (311 MHz pixel clock) results in drop-outs but I'm not sure if the GPU or the converter is the culprit; I'll keep testing.

I also tried a 12in 1.5GHz PB with the 64MB Go5200 but can only get 1920×1080 at 60 Hz to work, and even that has occasional drop-outs (but 1920×1200 at 60 Hz on a 23in acrylic ACD works fine – go figure...). Modes that are soundly within the 165 MHz pixel-clock limit for single-link DVI – I'm aiming even lower and don't exceed 154 MHz – all resulted in a black screen but with the screen's menu curiously correctly reporting the mode I defined.

My totally uneducated guess is that OS X, at least on the machines I use, tries to output a dual-link signal if the (horizontal?) resolution exceeds a certain limit (maybe 1920 pixels?), even if the hardware isn't technically capable of doing that. The fact that 2048×1152 at 60 Hz doesn't display via single-link but does via dual-link (both tested on the 15in) even though the pixel clock is just 156 MHz might support that hypothesis.

The question is, then: How to make OS X output single-link signals regardless of the horizontal resolution so I can hook up the beast to the little 12in?

 

I'd thought of that which is why I kept the PCLK under 154 MHz in my experiments. However, I don't know if the 12in actually has tweak TMDS transmitters.

I wasn't aware of that; many thanks for clearifying this. Another reason to hate "1080p" and other uselessly low 16:9 resolutions.

Next step is to try my 1.33GHz mini with the combo

 

Small update: Thought I'd try the screen with a 1.33GHz 12in PowerBook running Jaguar, since it predates the dual-link DVI matter. A great idea indeed...

Using the active DVI-to-DP adapter, the screen is recognised and several resolutions up to 3840×2160 are offered. None of them work and the screen remains a solid black. I also get occasional corruption on the internal LCD. Using a straight DVI-to-HDMI connection causes both the "4K" monitor and the PowerBook's LCD to get corrupted beyond recognition and that's that.

 

It's not a PowerBook, but... I can coax 1280×720 in HiDPI out of a 2006 MBP running Lion on this monitor. I wonder if Mountain Lion allows going higher. Actual resolution is 3840×2160@30Hz.

 

Small update: MBP is now running 10.8.3 via MacPostFactor; still won't go higher than 1280×720 in HiDPI. Time to fire up Software Update.

 

Another small update since I acquired an IBM "Bertha"...

- 12in 1.33GHz PowerBook with 32MB GeForce FX5200: unusable due to heavy corruption on both internal and external screen. Corruption appears as soon as the grey Apple logo. Tested with Jaguar and Tiger.

- 12in 1.5GHz PowerBook with 64MB GeForce FX5200: unusable due to heavy corruption on both internal and external screen. Corruption appears as soon as the grey Apple logo. Tested with Tiger.

- 15in 1.67GHz PowerBook SLSD with 64MB Radeon 9700 and single-link DVI: 3840×2400 at 13 Hz works at 32,768 colours but framebuffer corruption appears like it does with the Dell display. Tested on Tiger and Leopard.

- 15in 1.67GHz PowerBook SLSD with 128MB Radeon 9700 and dual-link DVI: 3840×2400 at 13 Hz works at "millions" of colours but framebuffer corruption appears like it does with the Dell display. Tested on Tiger and Leopard.

- 1.33GHz Mac mini with 32MB Radeon 9200: 3840×2400 at 13 Hz works at 32,768 colours. No framebuffer corruption. Boots at 1920×2400 but OS X Tiger and Leopard switch to full resolution when WindowServer loads. Jaguar displays a broken greyscale 1920×2400. OS 9.2.2 only displays up to 1920×2400 as well, trying to switch to full resolution results in heavy corruption. Several lower resolutions work but others don't.

- 15in 500MHz PowerBook Ti with 32MB VTBook: 1600×1200 at 60 Hz is highest resolution offered in OS 9.2.2.

- 15in 800MHz PowerBook Ti with 32MB Radeon 7500: 3840×2400 at 13 Hz works at 32,768 colours if in clamshell mode - if the internal LCD is also active, only 256 colours are possible. No framebuffer corruption. Tested on OS 9.2.2, Puma and Jaguar.

 

Changed thread title since it's about 3840×2160 and 3840×2400 now.
Added more data points to previous post.