XPS 13 Developer Edition (2015): Rushed

July 29, 2015

Dell’s XPS 13 Developer Edition from 2015 has some nice hardware, but it was rushed to market. The machine isn’t usable as delivered. Either no QA testing was done, or an impossible deadline was imposed. I’m pretty sure it was a deadline. It took the managers a while to realize this is a problem, but they finally decided to act by no longer selling it until they fix it. Someone with basic Linux sysadmin skills and some time to install the various fixes can get it working quite well so long as they aren’t a fast typist; key repeats are only mostly fixed as of now. With the fixes, I find it can still fail to resume from suspend, but it doesn’t happen often and leaves nothing logged to indicate the problem. Overall, I like the machine more than I should.

I went for a model with the 1920×1080 display and no touchscreen because I don’t like glossy displays. I do like resolution, and this is plenty for the small size. I’ll be using font anti-aliasing for a while longer; probably could turn that off with the higher resolution model.

Dell shipped it in a cardboard shipping box that distinguished itself by including a plastic handle so it can be carried around like a briefcase. Inside that is the power supply and cable, and a black box. A very nice looking black box. Inside that is the XPS 13 with foam above and a plastic tray below that is very well fitted. Clearly a lot of though went into this, more than I have managed to convey. Underneath the computer is a folded paper on using MS Windows. I know the Developer Edition uses the same hardware as the XPS 13 with Windows pre-installed, but I didn’t expect it would include the same, but useless, documentation. Not a big deal, but maybe a harbinger.

When turned on, the XPS 13 quickly boots and brings up a legal document. Fun stuff. After a short delay, although long enough that I thought it would let me read the document, a video starts playing full-screen. The video cannot be stopped, and trying to switch away doesn’t work. Alt-tab brings up the window switching menu, but it doesn’t switch. I also couldn’t mute the audio or change the volume; I’m used to pressing two keys to get the functions like volume control, but only one was required. I eventually figured that out, but it did make the compulsory video rather annoying. What made it obnoxious was that it was just an animation of logos zooming about put to music that meant nothing.

With the video done, I got back to reading the legalese. I needed to scroll the text, so I got to use the mouse. It occasionally quit working for two seconds or so before accepting more input. There is a fix for this from Dell, but not on the part of their website for supporting purchased products. That is, if you were to purchase a XPS 13 Developer Edition, log into your account on Dell’s site, find the item you bought, and try to download fixes, then you won’t find them. The fixes are on Dell’s website, just not there. It is apparently reserved for Windows related fixes and system firmware, aka BIOS. A search engine is the best way to find the Developer Edition fixes. Once applied, the mouse no longer ignores input, but occasionally when trying to scroll with it, the system will respond like alt-tab is down and cycles through the windows super fast. I have no idea how to reproduce the issue. It hasn’t happened in the last couple of weeks, but I’m not sure it won’t happen again.

Soon after that, I got to try typing. It regularly repeated key inputs until another key was pressed. This didn’t take fast typing to observe. A BIOS update mostly corrects it, but people who type really fast report that the change only mitigates the problem. The issue affects Windows as well. Considering that keyboards are common computer hardware that have generally worked well for decades, and that Dell botched it in 2015, it is amazing the rest of the hardware came out as well as it did. The group within Dell that put Ubuntu Linux on the XPS 13 clearly had a hard time dealing with this hardware.

After this, it was time to update the installed software. The Ubuntu Software Updater ran until it got to grub, then seemed to hang on the update while still responding to user input. After waiting half an hour, I killed it and what seemed to be a related process that was eating processor time. Then I used apt-get from a shell and ran whatever command it told me to run when it complained about some problem. Since then, updates have worked correctly. I have to wonder if an uncorrected hung update would render the system unbootable.

Following that, the system needed updates for the graphics to resume reliably from suspend. I still have an occasional issue with it, but matters greatly improved. A remaining issue is how the screen brightness automatically adjusts: it darkens for a mostly dark frame, brightens for a bright frame, and offers no user configurability at all. I was worried this would be an issue for working with photographs, but the screen’s limited color gamut, at least compared to another display I have, has proven a much bigger issue. I just have to learn to avoid over saturating the color.

Other than that is an occasional crash for no apparent reason. I’ve had it happen shortly after booting the computer and starting to browse the web. It was occurring twice a week, but hasn’t happened in a couple weeks or so; maybe something was fixed.

The XPS 13 Developer Edition was in no condition to ship. Asus did a much better job with their Eee PC line; they might have been limited by their Linux distribution, but they worked fine right out of the box. Still, I’d rather not buy a computer with Windows pre-installed, and I like that Dell is going through some effort to support Linux, including getting patches into the mainline kernel to improve hardware support. I’m guessing the XPS 13 issues were unexpectedly time consuming to fix and management didn’t want to wait.

The Sigma 18-35mm f/1.8, firmware updates, and auto-focus

July 27, 2015

Here is the quick summary: the firmware update for the Canon mount Sigma 18-35mm f/1.8 (2014-8-22) did more than add support for the EOS C100, as claimed by Sigma. It also changed the lens ID from 137 to 150, and seems to have improved auto-focus accuracy, although not precision.

I got one of Sigma’s 18-35mm f/1.8 lenses to go with a new Canon EOS 70D over a year ago. At a New Year’s event with a local band that includes a neighbor of mine, I took a bunch of pictures with this combination. The result seemed to work pretty well in spite of the low light at the outdoor venue. However, I have found that many images I have taken with the lens since then have not been in focus when using the optical viewfinder. This is a fairly common problem with Sigma lenses, although it doesn’t account for its early good performance. I’m guessing that at the New Year’s event most of the pictures had a deeper depth of field from focusing far enough away.

To deal with the problem, I got one of Sigma’s dock gizmos. I printed out a focus test page and made a table that I filled out with the adjustments needed. Every time I used the dock, the Sigma software asked about updating the lens firmware. I always refused because Sigma claims they just added support for a camera I don’t have. I don’t like to update things unless the update is actually beneficial. It is a way of limiting the chances of dealing with an update that breaks something.

Auto-focus calibration tool

Auto-focus calibration tool

The attempt at improving auto-focus didn’t go well. I got very contradictory results from two attempts, each starting from no adjustments, and neither improved the results. I figured the paper at a 45 degree angle was to blame, so I built a focus target out of Lego. When I cleared the adjustments on the lens before testing, I decided to update the lens firmware just to keep the software from incessantly asking about it. Every test I did with the Lego target suggested the lens was fine. Some tests with more common subjects suggest the accuracy is decent, but the precision still isn’t as good as with Canon lenses, so it is still a good idea to take several pictures and review them.

The software I use for keeping track of my photos, Digikam, did not at first identify this lens. Instead it called it lens 137; it has since been updated. I think the Canon protocol uses an 8-bit unsigned integer to identify the lens model, although now additional information like the focal length range is needed to identify a specific lens model. Since I updated the firmware, Digikam identifies the new images as being taken with lens 150.

I don’t know if this change from 137 to 150 is needed to make the lens work with the EOS C100. It is possible that the change will affect how the lens and camera work together. From what I’m seeing, it has a favorable effect on auto-focus performance with my EOS 70D. I don’t know why Sigma wouldn’t mention this, and I really don’t like the short list of changes common in the photographic industry for such updates. I have suspected that some changes are omitted from the public list of changes, and my experience with Sigma’s 18-35mm f/1.8 lens deepens that suspicion.

Long commands on Windows with SCons

January 15, 2015

At my job, where one of my tasks is to handle builds for Windows software using SCons, I recently moved from using SCons 1.2 with some custom modifications to an unmodified SCons 2.3.4. The change comes along with a move to using a newer Visual Studio while still supporting builds with an older one. The newer SCons has trouble with issuing some commands, just like the older version. Neither version can run programs that have whitespace in their path if the entire command is longer than some threshold. The custom modifications I made were to correct the problem, but this time I wanted something less custom and easier to support. Here is a link to the solution I developed; read on for the details.

With shorter commands, SCons issues the commands about the same way it does on Linux, and it works fine. Longer commands run into trouble on Windows; I’m told it has to do with the C runtime libraries. SCons works around this by placing most of a long command into a temporary file and then passing the name of the file preceded by a ‘@’ character as the first command line argument. Microsoft’s compiler and linker will read the temporary file for their arguments.

The implementation of this has a flaw that makes it useless using default installations of Visual Studio. SCons first puts together the command line as though no special long command handling is required. If the result is too long, the command is modified to use a temporary file but is parsed incorrectly; the program to run is taken to be all the characters up to the first whitespace. This makes the command to run “C:\Program”, which isn’t a program, or even an existent path. Everything after the first whitespace is put into the temporary file. It may start with “Files (x86)\Microsoft Visual Studio 10.0\VC\bin\cl.exe”, for example.

I found an attempt at getting SCons to use long commands written by Phil Martin. He provided SCons with a different way to spawn processes. Unfortunately, it doesn’t handle the whitespace issue. By the time the spawn function is called, SCons has already modified the command to use the temporary file. Nevertheless, his implementation was a good place to start. Like his implementation, mine also requires PyWin32.

I modified it to detect the use of a temporary file. When used, the spawn function opens and reads the temporary file to rebuild the complete command line. Then it figures out the whole path to the program, including whitespace, and separates that from the arguments. I also made a modification to produce better error messages from CreateProcess().

Finding the path to the program works best when there is some delimiter in the program path. It is common on Windows to enclose paths that have whitespace with double quotes. The command constructed by SCons using the default program paths lack this delimiter. I solved this by supplying new complete paths for all programs used in Microsoft’s toolchain. It is quite a bother, but I did it the best and most complete way I could figure. This includes creating some build configuration options for several paths, and making two build environments: one for x86 targets and another for amd64 targets.

Hopefully this will help someone else. I really don’t understand why this bug has been around for so long considering that whitespace in paths on Windows is very common.

Personal Cloud

July 13, 2014

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A cloud so personal, it senselessly gathers your intimate details that it doesn’t need.

A good combination

January 21, 2014

I tried this combination over the weekend: hot chocolate and chocolate flavored caffeinated marshmallows. The marshmallows had a couple of spots with a candy like flavor that they lack when eaten without hot chocolate, but otherwise the combination worked very well. I suppose marshmallows without a chocolate flavor would work, too, but these caffeinated ones don’t come it that flavor.

Replacement I2C kernel module for Raspbian

January 8, 2014

A while ago, I got I2C repeated starts and SMBus support to work from the Linux kernel on a Raspberry Pi. I recently built a new 3.10.25 kernel from the foundation’s kernel fork on Github and updated my own fork of their fork with just the I2C update in a new branch. In the process, I managed to misuse git so that commits now attempt to go to the Raspberry Pi Foundation’s kernel fork rather than my own. I tested the module on the copy of Raspbian that I have. It is running the 3.10.24 kernel, but is quite happy with the new kernel module (or for 3.10.37, or 3.12.24) and my MLX90614 test program. I also built the kernel module for the BMP085, but it looks like that requires more than just a kernel module file to get it working. No big deal for me; I’ll just replace the whole kernel.  I just wanted to see if I could make it really easy for someone else.

To use the updated I2C module, first download it. The file will need to replace the one in /lib/modules/<kernel version>/kernel/drivers/i2c/busses. You may want to keep a copy of what is already there. After copying it, check to see if the i2c-bcm2708 module is loaded. If not, load it up and have fun! If it is, you can either reboot or unload the i2c-bcm2708 kernel module. Before unloading will work, any dependent modules must first be unloaded. It wasn’t loaded for me right after boot, so it hopefully won’t be any trouble.

Update: I finally got the code up on Github. I hope the kernel module has been working out for anyone who has tried it. Please do leave a comment about any success or failures with it. I have yet to get any feedback, so I only have my own test case to claim that it works.

LumiQuest softboxes and flash zoom settings

January 2, 2014

It is good to have diffuse light for soft shadows. To that end, when I can’t aim the flash at a ceiling I use LumiQuest softtboxes because they aren’t super pricey (although there are cheap competitors from beyond the USA now), and they are very portable. This isn’t an advertisement for the product, though; I’m not getting paid. Instead, this is about an investigation I did into how to get the best results from the LumiQuest’s Softbox and Softbox LTp.

Happy Thanksgiving!

The LTp softbox is directly over the minifigs and very close

I got the LTp to help with some Thanksgiving dinner pictures of Lego minifigures. It is almost too large for something attached to a flash, and it did take a few tries to keep it from falling off. It was facing downward to be an overhead light, but that made falling extra easy.

I wanted the light to be as even as possible, so I used the pull-out light scattering lens of the flash. This put the flash’s zoom head into its 14mm setting, which is really just the 24mm setting with the lens applied. The lens is made of some plastic like material and absorbs some light, which was also helpful because otherwise the flash was too bright. The flash in question here is the Yongnuo YN568EX II, which is working out quite well for me, but that could be the topic of another post.

Brightness uniformity test

Brightness uniformity test

Afterwards, I wanted to investigate what works best with the LTp to make the softest shadows. It makes sense that the light will need to be uniformly bright across the light scattering surface of the softbox for the best results. I took pictures of the LTp with different flash zoom and power settings to get an idea of the uniformity. The exposure was the same for all pictures (f/16, 1/125sec, ISO 100). The resulting test is not indicative of overall brightness because most of the images have over-exposed areas. They do, however, clearly show that the 14mm flash zoom setting does provide the most uniform light over the surface provided by the LTp softbox. The 24mm setting isn’t much worse, but the 105mm setting looks like it should make the LTp perform the same as a much smaller softbox.

Next, I decided to see what effect this has on the quality of shadows. I put a cardboard tube on frosted glass so that I could photograph the shadow on the glass, and because I had the glass already setup. I later discovered that the shadow on the glass was sometimes filled in with light from the flash reflecting from other surfaces in the room which obscured what the shadow would have been with light only directly from the softbox. The test images also had a shadow cast by the tube onto itself, which turned out to be mostly immune to the problem. It made for small test images, but I think they worked out well.

Shadow quality test

Shadow quality test (take link for bigger view)

For a more complete test, I also tried my old LumiQuest Softbox (the one with a notch in what otherwise would be a rectangular light scattering surface), a bare flash, and a misused Sto-Fen Omni-Bounce. I varied the flash power, but not the exposure (f/4, 1/160sec, ISO 100) or distance between the flash and tube (about 740mm, or 29 inches). In all cases, the 14mm setting required quadrupling the flash power and the modifiers required doubling it. The bare flash at 24mm used 1/32 flash power. The 105mm flash zoom setting required changing flash power, but it wasn’t so consistent.

The results show that the LTp softbox responds more to the flash zoom setting than the other LumiQuest softbox I have. The LTp improves with the 14mm setting over the 24mm, but the loss of light from the flash’s scattering lens will sometimes make 14mm too dim. Other flashes may fare better, but I think most will be similar if they don’t use a glass scattering lens. Using the LTp with the 105mm setting makes it about as good as the non-LTp softbox at 14mm or 24mm.

The LumiQuest Softbox (non-LTp) produces shadows with a negligible difference with the 14mm and 24mm zoom settings, but does get worse at 105mm. The bare flash gives the expected shadows with hard edges, but it does seem to be very slightly softer at 105mm. This suggests the zooming action changes the uniformity of the brightness across the flash head.

Finally, I tried a Sto-Fen Omni-Bounce pointed directly at the tube. The Omni-Bounce is a light scattering device that doesn’t add much surface area like a softbox does. This makes it half of a light diffuser. The other half is supposed to be the ceiling and walls of the surrounding room. The little card included with the Omni-Bounce states that it should be pointed at the ceiling and not the subject. This test shows why. I have seen some people misuse their Omni-Bounce by pointing it directly at their subject while inside a convention center with high black ceilings, but that just results in wasting flash power.

CD-R Stack as a Background for Pictures

October 12, 2013
Background setup

Background setup and messy desk

I’ve been using a stack of CD-R’s as the background for several images of Lego minifigures. The CD-R’s are lit by flashlight (a silver Hexbright). In front of the flashlight is a color filter and a light scattering filter, both really intended to be used with a flash. The position of the CD-R’s and the two Star Wars minifigs in front are unchanged from the recent photo “Don’t let this happen to you”. The examples shown here all use the same color filter, but I also used violet and red-ish ones, as well as none at all.

The background result is affected by the relative position and orientation of the flashlight, CD-R stack, and camera. This makes using a flash in place of the flashlight really difficult. Also, I usually had the Hexbright at a low brightness setting, so it really was flashing, but it bothered the camera more than me. All of these positions and orientations provide lots of variables to play with to make a number of interesting effects for colorful abstract out-of-focus backgrounds.

Mom, I can see straight!

Mom, I can see straight!

Some of the light going through the CD-R’s makes nice vertical columns of highlights. There are four of these columns: one on either side of the central spindle pillar thingy (I don’t know what that is called), and two further away that seem to be reflections of the first two. Getting all four in the same picture is nearly impossible, but two is pretty easy and three isn’t difficult. Some prism-like effects are visible in those highlights, and the CD-R’s colors the light a bit green. I’ve got two or three bands of CD-R’s in the stack, so the exact shade of green varies a bit. I also looked at some DVD-R’s, but they are a boring white. I think I’ve got older ones that’ll color the light a bit red, but I haven’t tried.

With this setup, horizontal bands over a limited vertical distance can be shown where the light passes between the disks. As a result, these bands are not colored by the CD-R’s. They are visible just under Iron Man’s left arm in “Looking for trouble”. The light also reflects between the surfaces of adjacent disks; this seems to create an odd pattern that can result in curved swirly lines that are more easily seen by a camera than eyes. The curvy swirlies are seen in “Mom, I can see straight” to the left of the minifig. Some placements of the camera versus the CD-R stack avoid this effect and have clear horizontal lines with beveled edges as seen near the minifig in “An explorer in a strange place”.

Looking for trouble

Looking for trouble in front of CD-R’s

With the help of a light in front of the CD-R’s (I used an on-camera flash pointed at the ceiling and nearby wall), a single vertical column of reflected light can also be put in the background. The reflection highlights look distinctly different from the highlights of light passing through the CD-R’s. Instead of aperture shaped highlights, they have horizontal bands that seem to be sections of the aperture shape. Since this light comes from a different source, it is a simple matter to make it a different color. This shows up in “Looking for trouble” with Lego Iron Man (sans iron). I used a CTO filter on the flash attached to the camera to help make the helmet look more golden, and it shows up reflecting off the CD-R’s.

This guy

This guy

What I’m most fascinated by are some horizontal bands in my picture “This guy” (lower middle of frame next to the minifig; not visible in the little thumby here, best seen after taking the link and viewing the image full size). Even though the stack is well out of focus, there are a number of thin bands. I’m guessing that the banding of horizontal disks caused similar banding in the out-of-focus light which can be made into thin lines by how the light from different bands are superimposed on each other.

The top of the desk is glass, so I usually have a flash under it. The effect works a lot better than some of the scenes of the evil Kirk in “The Enemy Within”. It also helped tremendously with my “Looking for trouble” picture; one flash lit the face and the other lit the helmet.

I also made a video to show how the background can change, but it really doesn’t give a full demonstration.

Adafruit’s Puft Cloud

September 9, 2013

There is a nice post on the Adafruit blog about the networks of stuff. It features this wonderful picture:

Adafruit's Puft Cloud

Adafruit’s puft cloud grabs hold of everything

A very happy looking cloud is grabbing everything in sight. It seems like the artist tried to think of the most harmless thing; something that could never possibly destroy us. The post is a short summary of a way to tame the puft cloud put forth by Limor Fried. There is also a Google+ page for it. The basic notion is to keep things open so that what is collected is known and how it is used can be limited and controlled by users. Given how companies love to keep everything proprietary, we may be doomed. But, maybe after a few more incidents like the Samsung Smartly-taking-away-your-privacy-through-security-flaws TV, companies might finally get the idea when users demand security they can verify. If no one outside the originating company can verify their device’s security, it is only a short matter of time until someone outside that company verifies the device’s lack of security. Such lacking security of a device used in the presumed  privacy of one’s home is a problem most people would rather not have, but a few will want to profit from.

I2C repeated starts implemented on the Raspberry Pi

July 13, 2013

Update: If you just want a kernel module for something close to kernel version 3.10.25, look here.

I’m working on a project that uses the Raspberry Pi and various sensors. One sensor is a MLX90614 IR thermometer; this communicates using SMBus. One of my goals is to avoid making the project specific to the target hardware, the hardware that actually runs my code. I want the code that communicates with the sensors to be Linux specific but not Raspberry Pi specific.

Communication with a MLX90614

Communication with a MLX90614

One of the problems a lot of people have had with the Raspberry Pi is with getting SMBus communication to work. SMBus is built on I2C, a way of managing serial communication between many devices with only two wires: clock and data. I2C is more flexible, while SMBus is made to be more reliable. As part of guaranteeing reliability, mostly in a multi-master setup, SMBus requires the use of I2C’s repeated starts for read operations. The I2C master driver for Linux on the Raspberry Pi does not support this, and I have been unable to find a patch or custom version anywhere that adds support. Most people have solved the problem by using code that directly interfaces with the Raspberry Pi’s hardware, ignoring the Linux kernel support altogether. This solution not only fails to meet my goal of avoiding code specific to the target hardware, it also won’t work well if more than one process on the same host attempts to use the I2c master hardware.

I decided to solve the problem by modifying the Linux kernel’s support for the I2C master of the Raspberry Pi. I succeeded. My implementation may not be the best or bug free (works for me is a weak guarantee), but it does allow for communication with a MLX90614 using the user-space (unprivileged code outside the kernel) SMBus interface provided by Linux. Since examples with SMBus are more difficult to find than I2C, here is my test code. I also tested with a BMP085 sensor using the support for it already in Linux. This sensor uses I2C rather than SMBus, and it also functions correctly. It doesn’t need a repeated start, but it gets one anyway.

To avoid causing extra trouble, I implemented repeated starts for a subset of conditions under which they could be valid. I focused on SMBus communication. With I2C, a slew of messages going back and forth can be requested, all with repeated starts, but this isn’t normally done or required.  Also, the hardware requires that once the first message has begun transmission, the second message be setup in the registers ahead of the stop condition. To make matters worse, there is no interrupt condition for this, so polling in a busy wait is required. I stuck all this inside the bcm2708_i2c_master_xfer() function of i2c-bcm2708.c so it isn’t in the interrupt handler. After the second message is configured, the interrupt handler is used to receive the data. That avoids additional polling at the cost of not allowing additional repeated starts.

If you’d rather see the kernel change in source control, I stuck it on Github. It is a 3.6.11 kernel, but not the latest revision out there. I’m still using it for now. There is no kernel or kernel module for download here because I’m running Gentoo on my Raspberry Pi and I build my own kernels. If I gave you my kernel, you may well find that something doesn’t work anymore.


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