All posts by eddy

Photoshop image rotation made easy

Windows

If you use Photoshop for scanning images, you often need to rotate the scanned image by a degree or two to get it lined up straight (placing it straight on the scanner bed can be almost impossible).

I used to use the trial & error method of guessing a rotation amount, trying it out, then adjusting it up or down until I got something that looked right. Eventually, I figured there must be an easier way.

And of course there is: use Photoshop’s Measure tool, which is a sub-menu option on the Eyedropper tool. Measure a horizontal or vertical line using this (the longer the better), then open the Rotate Canvas / Arbitary dialog and you’ll find Photoshop has automatically filled in exactly the right angle for you.

This handy tip courtesy of Pixel-Techs where you can also find a detailed example, with screenshots.

Eircom’s new DSL packages

Networking

After several weeks of rumours, Eircom officially announced their new DSL packages today.

It’s not a bad deal. All existing customers will see improvements of between 2x and 4x in total downstream bandwidth, depending on the monthly subscription. The best improvement is for Home+ users, who jump from 512 Kb/s to 2 MB/s. Smart Telecom’s equivalent deal is still significantly cheaper, but offers only 128 Kb/s instead of 256 Kb/s upstream.

There was an opportunity for Eircom to also increase upstream bandwidth, but they appear not to have done so. Several people are speculating that this is to discourage business users from switching to VoIP, thus undermining Eircom’s voice revenue; this could well be the case.

No discussion at all of bandwidth caps – in light of Smart Telecom’s cap-free policy, Eircom may have decided to leave it be for now, privately targetting only those users that are blatantly abusing it.

Interesting times…

Pesky ATA/66 disk caddies

Windows

In an earlier entry, I mentioned the problems I had when upgrading an old ATA66 drive to a shiny new ATA133 drive. The old drive had been in an ATA66 removable disk caddy, and it didn’t behave too well at ATA133.

I resolved that problem by simply uninstalling the drive caddy and connecting the new drive directly to the motherboard via a decent ATA133 cable. (HDTach still shows the performance as a little choppy, but it’s not bad, averaging around 50 MBps transfer rate and peaking at 78 MBps.)

Well, I had a 120 GB drive die a few days ago, also in a caddy. Maxtor sent me a replacement, and once again, it was ATA133. Exactly the same problem as before – really bad performance, making the PC close to unusable.

I didn’t want to give up another caddy, so I buckled down and did a bit of research. It’s been well documented that Windows XP will drop down to PIO mode for hard disk transfers after six DMA timeouts have occurred. However, my problem was different – I suspected transfer errors (which result in a retry) rather than timeouts.

You can check which mode Windows is currently using for a drive by going into System / Hardware / Device Manager, then opening IDE / ATAPI controllers and double-clicking the Primary or Secondary IDE controller. Under Advanced Settings, you’ll see the current transfer mode used for each drive.

I knew from the PIO/DMA discussions that the registry key HKEY_LOCAL_MACHINE \ SYSTEM \ ControlSet001 \ Control \ Class \ {4D36E96A-E325-11CE-BFC1-08002BE10318} was responsible for configuring the ATA IDE driver. However, documentation of the various fields was hard to come by. I eventually figured it out by trial and error.

This key has a Default value of “IDE ATA/ATAPI controllers”, which is a handy way to check you’re in the right place. If you’re searching for it manually, it’s usually about the 10th class down in the (gigantic) list of classes from the top, so it’s easy enough to locate.

Inside the key are several numbered sub-keys: 0000, 0001, 0002, etc. 0000 is for the IDE controller, 0001 and 0002 are the primary and secondary interfaces. If you have multiple IDE controllers (e.g. SATA and PATA), then there will be more than three keys here – be careful to modify the correct one! The SATA controller is usually listed before the PATA controller, but you may just need to use trial and error.

Anyway, once you have identified the correct subkey, corresponding to the interface the problematic drive is attached to, you’ll see a few sub-keys:

  • MasterDeviceTimingMode – set to the fastest supported transfer mode when the drive initialises.
  • MasterDeviceTimingModeAllowed – defines what modes are supported by Windows; usually set to 0xFFFFFFFF, but we can tweak it to stop certain modes being used.
  • MasterIdDataCheckSum – I believe Windows uses this to detect when a new drive has been attached to the cable. If you delete this key, it forces Windows to treat the drive as new next time it boots up, and restore full DMA access. This is one way to force a drive that Windows has reduced to PIO mode back to UDMA mode again.

(The same settings also exist with a Slave prefix; which set you modify depends on whether your drive is the master or slave.)

Let’s look at the MasterDeviceTimingModeAllowed value in more detail. This defines a 32-bit mask, allowing up to 32 options to be individually permitted or prohibited. The default value of 0xFFFFFFFF means all supported operations are permitted. By selectively turning off certain bits, we can make Windows avoid using those features. These same bits are reflected in MasterDeviceTimingMode, so that’s a good place to start.

On my UDMA6 drives, MasterDeviceTimingMode was set to 0x20010, which is 0x00020010 in 8-digit hex. I also knew that 0x00002010 was UDMA2. It seemed logical that the in-between positions corresponded to UDMA3 (0x4010), UDMA4 (0x8010) and UDMA5 (0x10010). The 0x10 at the end is probably multi-word transfer, though I haven’t confirmed this.

Right so. To disable, for example, UDMA5 and UDMA6 (ATA100 and ATA133 support respectively), we just need to turn off the appropriate bits in the Allowed mask. Instead of 0xFFFFFFFF, we can use 0xFFFCFFFF. All the other modes up to and including UDMA4 (ATA66) will still be allowed.

My problematic drive was attached to the secondary master IDE interface, so I went ahead and set MasterDeviceTimingModeAllowed for that interface to 0xFFFCFFFF, then rebooted. Sure enough, Device Manager now shows that the drive is running UltraDMA 4 instead of UltraDMA 6. Better, the performance is now usable again, averaging around 20 MB/s transfer rate. I suspect the caddy is still introducing errors (HDTach is a bit choppy still) but it’s hugely better than it was before.

This is crying out for a little applet to let you tweak the individual bits in this mask from a nice GUI. Perhaps I’ll write one if I get some spare time…

Host fingerprinting

Networking

The technique of OS fingerprinting has been well documented. It lets you identify the operating system used by a remote host with a fair degree of certainty. Indeed, OpenBSD even supports this in its filter engine; for example, you can write a rule that assigns mail traffic from Windows machines to a lower-priority bandwidth queue than that from other machines (since such traffic is usually the result of a virus).

However, researcher Tadayoshi Kohno has come up with a much more sophisticated approach, based on measuring clock skew across TCP packets. The idea is that every machine has a slightly different skew to their internal clock, and almost all TCP stacks timestamp packets using their internal clock as a reference point. By identifying the clock skew used for a particular PC, e.g. a laptop, you can track that machine’s movement as it moves around the Internet, perhaps connecting from several different countries or via different dial-up nodes.

All very ingenious, and with no end of big brother implications. Read more in this article at ZDNet Australia, or for the full technical details, check out his original research paper.

iPod Volume Control

Technology

2004 was definitely the year of the iPod. I bought one, my brother bought one, my sister brought one, and even my Dad bought one.

Unfortunately, though, iPods sold in Europe have their maximum volume capped compared to similar US models – in fact, the maximum level is about 30% lower on the EU models.

This is apparently to comply with EU legislation. Unfortunately, because it affects line-level output as well as headphone output, it causes all sorts of problems when you use something like an iTrip or connect the iPod to your hi-fi or car radio’s line-in – the iPod volume is significantly lower than that of the other equipment, so you spend a lot of time adjusting volume as you switch between your iPod and radio or CD.

There have been several hacks that attempt to overcome this by tweaking a volume compensation tag in each MP3 file you download to your iPod. However, these are not ideal – you have to remember to do it whenever you update your play list.

I finally found a utility that did what I really wanted: just remove the cap entirely. The utility is goPod and it simply adjusts a field in the firmware to indicate that capping is no longer required.

It works really well. If you have an iPod in Europe, you need this.

A decent registry cleaner

Windows

Over time, the Windows Registry accumulates dead and unused class keys, installtion keys, and other cruft which can gradually slow down the operation of your PC. If you notice the Start Menu taking longer to appear, and Explorer appears sluggish when opening files, it may be time to give the Registry a clean.

I’ve been looking for a good Registry cleaner for a while, and I finally found one: EasyCleaner.

Not only is it free, it also does a nice job of finding dead shortcuts, temporary files that are no longer used, abnormally large files, and plenty more. Particularly useful is the ability to find all large files and directories on a particular partition, to give you a heads up on where all your disk space has gone.

Recommended.

Google do it again

Networking

From a map of Dublin to … a map of the whole United States. But this one’s Google-style.

http://maps.google.com/ is yet another cool-looking application to come out of Google Labs.

It has a funky real-time dynamic-HTML interface that lets you interactively zoom in and out of maps, drag-scroll using the mouse, and (very cool) do location-sensitive searches.

For example, if I search on ‘pizza in st paul, mn’ Google will jump to the St Paul, Minnesota section of the map and then highlight all the Pizza shops on the map. I can then click on individual jobs for more details, or even get directions there.

Let’s hope this makes it to Ireland someday…

(If you’re interesting in how they implemented the slick user interface, there’s a good analysis here. Also check out this amazing satellite map of Switzerland, which has a similar interface, and this Java-based map of Ireland / Europe.)

Finding your way around Dublin

Useful Links

A friend just sent me a map to his house using a website I hadn’t seen before: http://www.dto-journeyplanner.ie/

It’s quite neat – essentially, a route planner for walking or cycling around Dublin. It recognised the name of my old employer and also the name of the house where I grew up, about six miles away, and had no problem plotting a route from one to the other.

Particularly handy for emailing directions to visitors not so familiar with Dublin.