Alcaic Research and technology, not iambic verse.

28Mar/120

Death of a friend – and resurrection.

Context

About a year back, after a system update, our 2006 iMac (ATI Radeon X1600 GPU) started acting flaky. Strange visual artifacts popped up sometimes, and the machine hanged (hung?) unexpectedly. This post shows what you can do to solve this problem - partially - and I am putting it up because it took me several days to hunt through old message board posts to find it.

Origin

The root cause of the problem appears to be (shame on you, Apple) some quality problems on a certain batch of GPUs from ATI and their mounting. With the ever increasing reliance of OS X on the GPU (Quartz Extreme etc...), the component starts to heat up and some of the electrical contacts fail. That is was temperature related was very apparent last summer.

Solutions

Browsing the web (I am not going to give you a long list of links, since most of this info was buried deep), the solutions fell into 6 categories

  1. Get Apple to replace the GPU subassembly. In my case: too late (even with extended warranty).
  2. Open up your iMac and clean it out, improving the airflow and (hopefully) reducing the temperature. Well, this was needed, and helped for about 3 days. Probably, opening it and cleaning it out just changed some mechanical strain that relaxed later on and the problem resurfaced.
  3. Reflow the soldering by using a hairdryer. Did not try this - the evidence seemed inconclusive and since I did not have a backup machine (I do have a backup of the data) to serve up the files in the house, I did not want to risk frying the GPU completely.
  4. Applying extra thermal paste. Didn't try this either.
  5. Using smcFan Control or Fan Control to increase the airflow. This is the one that convinced me this is the root cause, because it helped. Most of the time. But the iMac did sound like a vacuum cleaner. Most of the time.
  6. Removing the drivers. You read that right. By removing the GPU drivers, the iMac falls back on using the CPU and basic gfx, and hence the GPU is not used and does not run hot/does not corrupt anything. There is of course a trade-off: some programs that use this to payback video, and games as well, no longer work well/at all.

The last option worked very reliably. And since I only use the machine as a server, it is also the cheapest.

What do I do ?

Assuming you want to try #6, here are the steps:

  1. Reboot in safe mode (hold the shift-key immediately after the startup chime)
  2. Go to /System/Library/Extensions/
  3. Move/delete files that start with atiradeonx1000 and atiradeonx2000
  4. Reboot.

Conclusion

I now have a stable machine again, but I am not happy with Apple. This appears to have been a widespread problem a while back, and a divergence of the quality level I have come to expect from Apple. That it is a 6 year old machine is not an excuse - it still runs the latest OS X smoothly (which always surprises me) - I expect the hardware to live until no longer supported by the latest OS.

11Jan/121

Things and Merlin

Chaos is my natural state. I live and thrive on constant input and movement. I focus when my environment is dynamic. I get bored when things are quiet. But from an operational, task and project management point of view, this often bites me in the posterior. Technology saves me. Specifically, Things (on my Mac and my iPhone) and Merlin (on my Mac).

The problem

Things and Merlin are great, however, they use two databases and didn't really integrate. That's why I was very happy to find that Merlin's support staff had written some scripts that allowed to move items from one to the other.

The snag: it messed up the dates horribly. Now, I have a rather special setup for my short date format in that I prefer yyyymmdd to dd/mm/yy or whatever else is your favorite. That probably has something to do with it. I had expected the OS to take care of this, but there you go. Additionally, it used the planned start date of an activity as the due date, while I wanted the planned end date.

Diagnosis

Looking inside the script bundle (use Show Package contents), which you can find at

~/Library/Application\ Support/Merlin/SendToMenu/Selection\ to\ Things.app/Contents/Resources/Scripts/main.scpt

I found that the applescript uses the parse quicksilver input function -- and this is the culprit.

-- read activity information
set TheDueDate to planned start date
set TheDueDateString to short date string of TheDueDate

… some code cut …

-- this string contains Things project name
set s to "#" & TheTag & " " & TheTitle & " [" & TheMerlinProj & "] > " & TheDueDateString

-- create the to dos in Things
tell application "Things" to parse quicksilver input s

This is what we need to change.

Solution

Using the applescript editor to open main.scpt, I tried various date manipulation doodas (google for them, you'll see that date formatting in applescript appear to be an arcane form of magic), and then realized that using parse quicksilver input might not be the optimal approach. Some tinkering later, this is the final result:

set TheDueDate to planned end date
set ActualCompletion to actual completion
set TheStartDate to planned start date

-- create other way
tell application "Things"
    set newToDo to make new to do with properties {name:TheTitle, due date:TheDueDate, tag names:TheTag} at end of project TheMerlinProj
    if ActualCompletion is 1.0 then
        set status of newToDo to completed
        end if
    end tell

It sends the todo, sets the due date for to the planned end date and if the task is completed, marks it as such. And this works nicely:

Activities in Merlin

Activities in Merlin

Todos in Things

Todos in Things

Next

Two things remains on my wish list: I'd like to use the schedule functionality to schedule at the planned start date and connect the resources in Merlin with the delegates in Things. To be continued.

Postscriptum

You can find my updated script here.

9Jan/120

Can 1dB keep you awake ?

Warning: if you're not an engineer, a math nerd, or are not feeling especially geeked out right now, this post will probably lower your faith in mankind.

The setting

The other night, as I was falling asleep, I was thinking about differences in how people approach, calculate and specify quantities. Specifically, I had always been used to thinking about power levels of lasers in milliwatt (mW) - while calculating power budgets for optical links in decibel (dB). Now, for some weird reason, I'd never stumbled across the need to know how much power increase 1dB represented. Sure, I knew that 0dBm = 1 mW, and had it drilled into my head that 3dB is a factor of two in power. But that night, I realized that I didn't know how much 1dB extra power actually meant, as a percentage increase. A blind spot if I there ever was one.

So, what would any sane person do then? There are a number of possibilities:

  1. Reach for your iPhone next to your bed, google for "1dB in percent". Go to sleep.
  2. Get up, find a calculator (or a calculator app, on your iPhone), type 10^0.1. Go to sleep.
  3. Forget about it. Go to sleep.

You can also be stubborn and refuse to go to sleep, or refuse to use technological crutches ("What would Leibnitz do?"). And so you lie awake and try to figure it out using mental arithmetic - how hard can it be? (my wife would definitely agree I was being "mental").

How to approximate 1dB

A few minutes later I realized things aren't always simple when logarithms are involved. But I finally reached an answer that made me sufficiently happy to fall asleep ("What!? You didn't get up and check!?"). This is the approach I took:

  1. 1 dB = 10.log10(ratio)
  2. so, 0.1 = log10(ratio)
  3. and hence, 10^0.1 = ratio
  4. this we can calculate by doing a Taylor expansion of 10^x around 0
  5. 10^x|0 ~= 10^x|0 + d/dx(10^x)|0.dx + O(dx^2) (ok, truncating after the first term for dx =0.1 is a bit of stretch, I realized I was underestimating)
  6. now, what was d/dx(10^x) again ???
  7. ah: d/dx(10^x) = d/dx(e^(x.ln(10)) = e^(x.ln(10).ln(10) = ln(10).10^x

And there I was stuck. How much was ln(10)? I knew that e was approximately 2.7, but somehow that didn't help me immediately. So I tried successive approximations:

  1. y = ln(10) meant that e^y=10
  2. y = 2 was clearly too small, and y = 3 too large
  3. how about 2.5? e^(2.5) = e.e.sqrt(e) = 2.7 * 2.7 * 1.6 (the 1.6 was a lazy approximation, since 16.16=256, and 17.17=289 - it was getting late) and that about 10 (more laziness - it was not clear at that moment that I was overestimating, but I got lucky, since I was underestimating due to the dropping of the higher-order terms)
  4. hence: ln(10)=2.5

And so the Taylor expansion gave me 1+0.1 * 2.5 = 1.25 or about 25% power increase. Zzzzzz.

One night later

You might now be surprised that come Saturday morning, I had forgotten all about my nightly calculus. I woke up, went for fresh rolls and never bothered to check. Of course, you can guess what happened when, after a full day without Taylor expansions, I lay down to sleep...

"@$^#^&%!!!" Was I going to get up? And then it hit me that I had been really stupid. There was a much easier way to figure it out.

  1. 3dB = 1 dB + 1dB + 1dB
  2. so, a factor of 2 = ratio.ratio.ratio, or in other words ratio = cubicroot(2)
  3. 11 x 11 x 11 < 2000 for sure
  4. 12 x 12 x 12 < 2000 as well
  5. 13 x 13 x 13 > 2000, so where between 1.2 and 1.3
  6. can we easily calculate something in between? Yes: 128 x 128 x 128 = 2^21 = 16777216/8 ~ 2100000 (And if you wonder why I would know that 2^24 = 16777216, you're definitely in the wrong place. It's the number of colors of a 24bit display, one byte each for red, green and blue).
  7. And that's 5% over, so we need to remove about 5%/3 = 1%-2% since this is a cubic root which brings us to around 1.25-1.26. So: 26% power increase.

In other words, I now spent two nights going to bed too late because of 1dB. Which makes sense, if you know that this might be the tipping point between the technical feasibility of two approaches. 26% means almost a third more power and hence also more heat dissipation. So there.

Verification

Make no mistake, I now went down to check:

  1. e = 2.71828 - check
  2. ln10 = 2.3 - with 2.5, I clearly overestimated, and got lucky with the higher orders
  3. approach 1: 10^0.1 = 1.258 - check
  4. approach 2: 2^(1/3) = 1.259 - check

P.S. For those of you still with me: the reason this all came up was due to some internal discussions on link budgets for different possibilities of next-generation PONs.

12Nov/110

Hack your weight part two

Seems I just needed an additonal pinch of Dukan. End result: 26.7 lbs in 6 months.

1Feb/100

Hello Markdown

Story

Falling in love with

  • the elegance
  • simplicity
  • ease-of-use

of Markdown.

'nuff Said.

Note

Not enabled for comments (as if I have any, ever...)

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24Jan/100

Hack your weight

Ingredients: 1 iPhone (or iPad mini) 1 download of the Hacker's Diet (http://www.fourmilab.ch/hackdiet/www/hackdiet.html) 1 purchase of Weightbot (http://tapbots.com/weightbot) 1 purchase of RunKeeper (http://runkeeper.com)

Works for me.