Trouble in Promise-land

What's the first thing you do when you've got a display that has tons of interfaces and bandwidth at its disposal? Try them all at once to see if anything breaks of course. Over the course of the past few days that's exactly what I did. Unfortunately I did find a situation where things broke.

For whatever reason, if you're doing a lot of writes to the Promise Pegasus while playing music (or any other constant audio) through the Thunderbolt Display's internal speakers the audio will eventually corrupt. You can hear exactly what I'm talking about below:

TB Pegasus Audio Issue by AnandTech

This is a recording taken of me listening to music on the Thunderbolt Display (via its internal speakers) while writing a couple hundred gigabytes to the Pegasus R6. Note the introduction of what can only be described as really bad noise at the 6 second marker.

If you stop music playback and quickly resume, the problem will still be there. You have to restart the application that's using the audio codec to recover from this point. From a hardware standpoint, the codec just needs to go through an off/on (sleep/wake?) cycle to return back to normal. If you do this however and haven't stopped the transfer, the problem will creep up again. Stopping the transfer while playing back music won't fix the issue either. You have to stop the transfer and restart the music playback application for it to go away.

The issue goes deeper than that. I went out and bought a Creative Labs X-Fi Go Pro USB sound card to see if the problem stopped at the internal audio codec or extended to all USB sound devices. Unfortunately, it does even happen if you're using an external USB sound card connected to the Thunderbolt Display. Connect the same sound card directly to your Mac or use your Mac's 1/8" stereo jack and the problem goes away.

I was worried that what may appear as noise through speakers could result in data corruption over USB transfers. I ran the Pegasus write test while copying a bunch of files to an SSD attached via USB to the Thunderbolt Display and never saw any corruption on the SSD. This appears to be limited entirely to audio playback.

What's truly bizarre is I can only get the issue to appear when writing to the Pegasus, hundreds of GBs of sequential reads don't seem to produce it. Short bursts of writes don't seem to cause it either. Sending tons of data across the monitor's Gigabit Ethernet, FireWire 800 and USB ports doesn't seem to trigger it either. It appears to be an issue with the Pegasus and the Thunderbolt Display. But which device is ultimately at fault? Is it a problem with the Thunderbolt Display or the Pegasus? Ideally I'd use another Thunderbolt storage device to see if the issue remained, but I couldn't get my hands on a LaCie Little Big Disk.

I thought of something else.

First I needed to test and see if perhaps the issue was related to ultra high speed transfers. As we've already shown, the Pegasus can push as much as 1GB/s over Thunderbolt whereas none of the other bandwidth eaters come even remotely close to that. To determine if the issue was data rate invariant I wrote to the Pegasus at different speeds ranging from 480Mbps all the way up to 7.2Gbps. I tried putting SSDs in the Pegasus as well as standard mechanical hard drives. The problem remained. I got audio corruption regardless of what drives were in the Pegasus or what speed I wrote to the drives. The problem wasn't related to transfer rates.

I also took apart the Thunderbolt Display to confirm there weren't any obvious issues on the controller board (E.g. putting the Thunderbolt IC far too close to the audio controller). Nothing obvious there either.

While I was doing all of this, Apple put forth a Thunderbolt firmware update the other day, however it didn't seem to address the issue either. So I went back to my testing.

Since the problem appeared regardless of how fast (or slow) I was transferring and all I needed was another Thunderbolt storage device to vindicate either the Pegasus or the Thunderbolt Display I turned to the trusty MacBook Air.

As I mentioned in our original Pegasus review, if you have two Thunderbolt equipped Macs and a Thunderbolt cable you can actually put one of the machines in target disk mode and access its drives via Thunderbolt on the remaining Mac. You don't get super high performance but you can get around 500Mbps. Since I had reproduced the audio corruption issue at an even slower data rate I decided to give this a try.

I booted the MacBook Air in target disk mode by holding down the 't' key after turning on the machine. My MacBook Pro was connected to the Apple Thunderbolt Display and a Thunderbolt cable connected the display to the MacBook Air. This was the same setup as the Pegasus, but with the MBA in place of the Pegasus.

I wrote to the MBA just like I did the Pegasus (from a file server connected over the Thunderbolt Display's GigE, transfer rates were capped at around 500Mbps from the file server). After a couple hundred gigabytes were transferred without any audio corruption I swapped out the MBA and connected the Pegasus. I copied the same files at the same rate from the same source. After no more than 7GBs were written to the Pegasus the audio stream started to corrupt.

Based on my testing I can only conclude that the Pegasus seems to be at fault here, not the Thunderbolt Display. Given that the Pegasus was introduced prior to Apple's Thunderbolt Display it's not all that surprising that this issue made it through to production. It's unclear what the root cause is but it's hopefully something Promise can address either through firmware or a driver revision.

Update: I'm still verifying that this is indeed a "fix" but it looks like if you use a USB sound card plugged into a USB hub which is then plugged into the Thunderbolt Display then the sound corruption doesn't happen. This seems to point at noisy power as being the cause with the USB hub acting as a crude filter. It's still not ideal but this may be a workaround for Pegasus users until Promise supplies a fix.

Windows/Boot Camp Experience Dissection
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  • repoman27 - Tuesday, September 27, 2011 - link

    I'm just going off the information available, like everyone else. Which is why probably half the statements I've made about TB thus far have turned out to be inaccurate.

    But the TB port is electrically equivalent to a mini DP port. There are no additional contacts. A TB port operates in either DP compatibility mode or in TB signaling mode. The 4 pairs of signaling wires are used for either 1 DP main link Tx or 2 TB bi-directional channels, both of which are capable of transporting (tunneling) a DP main link. As far as I can tell at least.

    I posted a block diagram earlier, which I'll post again here, although I need to clean it up a little as my current theory of things Thunderbolt is now a bit more plausible. http://i54.tinypic.com/8zdwci.jpg
    Reply
  • repoman27 - Monday, September 26, 2011 - link

    I just noticed that my math was a little too quick and dirty. There's only one FireWire 800 port on the ATD, not two. So actually a second USB 2.0 controller or memory card reader were not out of the question at all, and probably just failed to make the cut due to cost.

    An optical drive would have required a SATA controller, which wouldn't have fit within the bandwidth limitations, and altogether would have added about another $50 to the price tag.
    Reply
  • repoman27 - Sunday, September 25, 2011 - link

    I find it bizarre the number of tinfoil hat conspiracy theorists that post comments on every review of an Apple product saying that the review was biased or nothing but a paid advertisement. I’m not sure how you could read this article and not believe that it was anything other than the most objective, informative and detailed review of the ATD yet published.

    Some points for consideration:

    There are plenty of reviews on Anandtech for products made by manufacturers that also advertise on Anandtech, yet these are never called into question. It’s just Apple, who to my knowledge have never actually advertised on a review site.

    While Apple does submit products for review, Anand went out and additionally bought his own ATD to dissect, so he actually paid Apple this time around. I doubt his review unit came packed in a box full of cash.

    There are no generally negative reviews posted on sites like these because the authors tend to spend their time reviewing products that have merit. Most of the major manufacturers don’t make a habit of bringing to market products that are clearly defective or devoid of any useful functionality. Apple makes solid products, and therefore gets a lot of positive reviews. Not that they are by any means above critique, but their standards tend to be higher than many of their competitors.

    Being objective is not the same as being impartial. The biases of reviewers will always show up in what they write, but stating opinions does not necessarily diminish the objectivity of the data presented.

    People who can’t figure out the timing of the posts on this site are baffling to me. When AMD, Intel or NVIDIA release new products, we get a quick blurb when it is announced and a full review a few days after it ships. When MWC is going on you get a ton of mobile device news, when IDF is going on you see a mess of Intel related posts, when BUILD is happening you’ll have a bunch of Microsoft stuff to check out. Yet so many people submit comments saying that this site has jumped the rails when WWDC results in a week of Apple posts.

    Why did the ATD get an in depth review? Because it marks the release of a highly anticipated piece of tech which was surrounded by many unknowns due to the fact that it actually forges into some new territory. Is there really a good reason why this site would NOT review this device? The only reason I can think of would be if a competitor had paid them off.

    If all those bitching about the quality or integrity of this site can point to better, more objective, more in depth reviews of these products, please feel free to cite references.
    Reply
  • Brigga - Sunday, September 25, 2011 - link

    As simple and probably silly as this sounds why doesn't apple have a docking station? Port replicators suck, but docking stations can be quite unobtrusive and easy to use (ie. no disconnecting of cables and second power supply stays where it is). Reply
  • repoman27 - Monday, September 26, 2011 - link

    Yeah, actually Apple solved the problem that way for five years back in the early nineties. The PowerBook Duo line had a docking port that worked with the Duo Dock and several other docking accessories. I'm guessing that they have enough bad memories of the problems inherent with those designs that they're shooting for a slightly different approach now. Reply
  • pesos - Sunday, September 25, 2011 - link

    I went out and picked up a TB display last night to pair with my 2011 mbp. I live in windows about 95% of the time and expected there to be no issues with the basic usb hub built into the display – unfortunately that does not seem to be the case. My Apple usb keyboard (also brand new) and dell usb mouse both hang/freeze/work erratically when connected to the back of the display, as does my Jabra pro headset. I can make the behavior 10 times worse simply by using hardware built into the display, such as the facetime camera. If I fire up Lync and start a video chat, my keyboard and mouse become nearly unusable. My basic testing under Lion appears to confirm this is an issue with Apple’s boot camp drivers as things work fine under OS X. Problem occurs both with win7 and win2008r2. Reply
  • shin0bi272 - Sunday, September 25, 2011 - link

    first world problems... Reply
  • Oli56 - Sunday, September 25, 2011 - link

    Anand, great review but it seems you completely overlooked the impact of the glass which can be negative to some users. I owned an iMac some time ago and the glass reflections were very disturbing to me and led to ocular fatigue. It is unfortunate Apple has moved to glass display for all its line of screens, fortunately we can still have a MacBook Pro with mate display as option but that doesn't exist for a 27" IPS screen which should really benefit from it. So basically glass maybe looks cool on display but when this is about to work all day with it, this is a nightmare. This is the only thing keeping me away from that screen, as the rest of it looks great. Reply
  • dmaffei - Monday, September 26, 2011 - link

    You never fail to impress... nice job old friend!!!

    Dan :-)
    Reply
  • StefanoT - Monday, September 26, 2011 - link

    so this really, really, is an Apple Display without DisplayPort?!
    If I'm not mistaken, just the other day DisplayPort was the way to the future, touted to eventually supersede DVI/HDMI. Indeed, it was almost too new to be widely supported! DisplayPort-enabled monitors, in my part of the world, are still few and far between. I was still waiting for the DisplayPort goodness to free me from carrying all sorts of miniDP adapters. To DVI, to HDMI, even (gosh!) to VGA!
    And now, suddenly, DisplayPort is to fall into oblivion, no longer supported by Apple, which was one of the main proponents and, ironically, now supports a standard that is built-on and, in a way, includes DisplayPort, and on top of that shares the same connector.
    Anand points out that the company has never got emotional about legacy stuff. If they did, the new technology would never get adopted. Apple is leaping to the future and can't get stop to deal with yesterday's interfaces. I would say that between one leap and another, you need to "land" somewhere. I'm not a fan of never-ending legacy support, but I'm still waiting for VGA to disappear from mainstream netbooks. Are they suggesting that I either ditch my oh-so-non-2011 devices (i.e., "not-released-in-2011", as opposed to "not-bought-in-2011") in order to use their new display, or that I buy an old, "non-Thunderbolt" version of their display, which sells for the same price? This doesn't make sense any way you put it... and to think that they had it so easy with Thunderbolt. The thing seems built with backward compatibility in mind.
    I didn't get if future displays will eventually support both DisplayPort and Thunderbolt. Perhaps once Intel makes it piece-of-cake easy, as opposed to "just add a chip to that big motherboard you've got back there, behind the glass". Perhaps once other companies start offering it. Or perhaps never, because why should Apple not leapfrog everybody again (including its customers), by switching to an all-new technology next year?
    Reply

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