Larry’s Personal & Tech ramblings

I’ve been using Windows Mobile phones since the early days of the MPX-200 and have used just about every phone that was released. For software testing, I’ve had to acquire the latest WM6 devices and have used them as my daily phone for minimum of several days. Here are my observations:

1) T-Mobile Shadow
Pros:
Excellent form factor - thin and light
Large, bright display
Good ergonomic keypad
Slide-up keyboard good for answering/hanging up
Cons:
Terrible battery life
Strange keypad layout causes slower text entry
Terrible camera
So-so phone reception

2) Motorola Q9H
Pros:
Built-in GPS
Large, bright display
Good phone reception
Fast CPU
Comes with extended battery
Decent keyboard
Cons:
TERRIBLE voice quality (sounds like talking to Darth Vader through a paper towel tube)
Heavy, bulky device
GPRS/EDGE data worked slowly and unreliably
Custom USB connector requires special cable or dongle

3) HTC Vox (S710)
Pros:
Good form factor for full-keyboard+keypad device
Large, bright display
Excellent numeric keypad
Excellent slide-out keyboard
Excellent voice quality
Excellent phone reception
Good GPRS/EDGE connectivity
Decent camera
Cons:
Little rubber covers warp and stick out (USB + MicroSD)

Conclusion:
The HTC Vox wins by a landslide. The only thing that kept me holding on to the Q9H for a few extra days was experimenting with the GPS, but since the EDGE connectivity was so hit or miss, I couldn’t get Google Maps to work because it kept timing out when receiving data. I guess the next phone for me will be the 3G successor of the Vox.

I’ve been sidetracked many times while trying to finish the latest version of Virtual CE. I’ve finally released the new version which now supports all Windows Mobile devices. For those of you unfamiliar with this product, it creates a real-time display of your WM device on your Desktop PC. It’s basically VNC in reverse. Here are some screen shots of it in action:

I’ve reduced the price to $10 and simplified the feature list to make it easier to use. Please give it a try:

Virtual CE

I was told by a customer that my game emulators did not display correctly on the Motorola Q9H smartphone.  I got hold of a loaner device and discovered the problem.  For some reason, the video memory is mapped in an odd way (reminiscent of the old Apple II).  This odd RAM mapping means that many games/multimedia applications will not run correctly on the Q9H.  I’ve written a workaround for my software, but the bigger question is how many devices/programs this affects.  My best guess is that this is the fault of the new TI OMAP 2420 CPU.  This chip has many 2D/3D capabilities, so it makes sense that the designers didn’t care much about how the video memory was mapped since most software would use the advanced capabilities of the chip and not write to VRAM directly.  I’m in contact with my friend at TI and will report more information about this problem as soon as I know.

It’s taken a lot longer than expected to release the latest version of my image viewer. Many other projects have gotten in the way, but I’ve finally wrapped up version 4 of PQV. The sales pages on Handango and PocketGear are not quite working yet, but the PayPal link works. The $14.99 license is per user, not device. A single license allows you to use the viewer on all your Windows Mobile devices and Windows Desktop. Here’s the new product page:

PQV 4.0

When you install the Pocket PC or SmartPhone versions, the Desktop PC version also gets installed.

WordPress (the company which hosts this site) collects some interesting statistical data on the people who visit the blog.  To me, the most interesting data is a list of the search words which direct people to this site.  Since I started including the JPEG and ARM keywords in my posts, I’ve seen a steady stream of people searching for basically the same thing: Free optimized source code for decoding JPEG/MPEG images on ARM devices.  I’ve done such searches myself and have come to the conclusion that it’s not available.  For anyone who has done research and invested tons of time and energy into writing optimized code, it is unlikely that they will be willing to give it away for free.  There are plenty of open-source and free projects on the internet that are valuable and professionally done, but there usually comes a point in a project’s lifetime when the author commercializes it to get compensated for the time invested.

I try to share my knowledge and experience with the developer community; I understand the frustration of wasting precious time locating resources or coming up with workarounds for problems outside of (or within) my code.  I also make a living writing software, and so I must write code which is worth compensation from my customers and maintain innovative solutions which compare well with my competition.  The geek in me would love to have an open discussion about the fastest way to decode Huffman encoded data or minimize the calculations in the IDCT, but as a consultant, that would be self-defeating.

The “trade secrets” are visible in the source code, but hidden in the object code, so licensing object code will incur less risk to me and therefore cost considerably less.  I’ve licensed my code to various companies for values ranging from several hundred dollars to tens of thousands.  The price varies according to the risk and time required.  Companies needing help with ARM optimization issues are encouraged to contact me.  The amount I charge for my time or code is usually far more economical than having other programmers spend time trying to invent what I’ve already  got working.

The two changes in 0.27 are the release of the Desktop PC version of SmartGear and the addition of the “PAUSE” button to the MasterSystem emulator (mapped as “Select”).

The product page for SmartGear is up –>SmartGear Web Site

You can now download friendly installers for Pocket PC and SmartPhone. The installers also install a Desktop PC version of SmartGear (never released before). A paypal button is at the bottom of the page to allow you to register.

I thought it would be useful to re-run the tests with the C version of my JPEG code. From the results it appears that memory bandwidth is the real limiting factor to the speed and the pixel colorspace conversion gets the most benefit from my optimized ARM assembly language. Also it appears that the OMAP gains more from optimized ASM than the XScale does. Here are the numbers:

C-Code:

PPC: thumbnail: 10.7 milliseconds, DC only: 968 milliseconds, full res: 3734 milliseconds.
SP: thumbnail: 25.1 milliseconds

Mixed C and ASM

PPC: thumbnail: 8.8 milliseconds, DC only: 830 milliseconds, full res: 2700 milliseconds.
SP: thumbnail: 15.1 milliseconds

The load times for the “DC only” and “full res” tests include the time taken to read 4.3MB of data from RAM through the WinCE file system.

These results make sense in that the real benefit of optimization comes from fixing the algorithms and reducing memory usage. The optimized ARM assembly code is certainly helpful in speeding things up, but won’t offer an order of magnitude improvement over what the compiler generates.

The great thing about the ARM architecture is that the more I look at a piece of code, the more ways I find to optimize it. The conditional execution, barrel shifter and optional setting of the processor flags create many opportunities for optimization. I’ve spent some more time optimizing my ARM asm JPEG code and now have some hard numbers to publish. I used a HP iPAQ h2210 Pocket PC (400Mhz PXA255) and a HTC Hurricane SmartPhone (195Mhz OMAP 850) to do the testing. I was able to load the file from RAM on the Pocket PC (to reduce file I/O delays), but not on the SmartPhone. The SmartPhone file system does not use RAM for file storage. The slow speed of reading from the miniSD card overtakes the amount of processing time in the tests, so the only test that was run on the SmartPhone was decompressing a 160×120 thumbnail image in RAM. All tests were to decompress the image to a RGB565 bitmap. The thumbnail test decompresses the 160×120 EXIF thumbnail image. The “DC only” test creates a single pixel from each MCU (the 3072 x 2304 image is loaded as 384×288). The “Full res” test decompresses every pixel of the image.

PPC: thumbnail: 8.8 milliseconds, DC only: 830 milliseconds, full res: 2700 milliseconds.
SP: thumbnail: 15.1 milliseconds

The speed difference between the two devices is to be expected considering the different processor and memory bus speeds. The “DC only” test is useful because it shows the relative speed of Huffman decoding. The file size is 4.3MB, so in 830 milliseconds the code was able to decode all of the MCUs and produce a single pixel from each one.

I’ve uploaded the sample image to my web server here: CIMG2209.JPG

The image was taken with a Casio EX-Z750 and depicts a relatively complex scene with many fine details. Like most cameras, the Elixim series saves JPEG images with 2:1 horizontal color subsampling (when set to maximum quality). It’s not unreasonable for a point-and-shoot camera like the Z750 to save images at a less than optimal compression because the image coming off the CCD isn’t that great to begin with. What irks me is that cameras like the Canon 20D do the same thing. With a good SLR lens and imager, the Canon should allow you to save full res color JPEG images.

Comments?

Let me start by saying that I’m not a big fan of Apple. Through the years I have always felt that they extracted a few too many dollars from their customers and left them with a few too few options. I’m glad Apple released the iPhone because it will stir up the mobile market a little and inject a few new ideas into the mix. The truth is that the iPhone is very much a 1.0 release - missing several important features and designed to be more of an improved iPod than a good phone.

1) As a music player it falls short of being usable; 8GB of memory is not enough to store even a fraction of most people’s music collections.

2) As a phone, using a touchscreen is a mistake. A phone shouldn’t require 2 hands to operate nor require your eyes to be focused on it to make a simple call. Get ready for iPhone-related car accidents.

3) Choosing AT&T was a big mistake if you’re touting your device as a great wireless web browser. EDGE network speeds can be OK, but they’re never great.

4) Most of today’s expensive smartphones come with a much more reasonable price tag when you’re roped into a high priced data plan for a minimum of 2 years. For the rate plans that the iPhone offers, it should be free with the 2-year contract.

5) Apple fanboys will drink the kool-aid as always and flaunt their wondertoy.

Even though HTC won’t admit they released the “Touch” as a response to the iPhone, I think we can see through the smoke. The Touch is a nice little Pocket PC, but it has the same issues as the iPhone; in other words, I would never carry one around as my main phone.

For me, the HTC S710 (Vox) is the epitome of SmartPhone design. It’s small, light, tough (no touchscreen) and has a convenient slide out keyboard. This is the phone I’ve been waiting for since Microsoft released the “SmartPhone” platform.

Let the flaming begin…

An odd title considering that JPEG is a cryptic image compression standard.  My idea of fun is optimizing code until there’s nothing left to improve.  I decided a few weeks ago to take the plunge and rewrite the 3 core JPEG decode routines to speed up my imaging code.  One reason was that the great majority of cell phones today are based around the TI OMAP architecture typically running at around 200Mhz.  These devices seem slow at working with images, so I thought I could help that situation by speeding things up to improve both battery usage and the user experience.

The important, “inner loop” routines of JPEG image decoding are the Huffman decoding of the MCU (minimum coded unit), the IDCT (inverse discrete cosine transform), and the output stage (turning the YCrCb pixels into RGB pixels).  All 3 routines together turned out to be only a couple hundred lines of ARM code, but the result of rewriting it from C was quite dramatic.  The original C code has been optimized and tested over a long period of time and was in good shape to begin with, but C isn’t so great at bit manipulation and squeezing the most use out of register variables.  It took several iterations to get down to the bare minimum of code, but I’m quite happy with the results.  I used ARMV5 instructions, but made sure that the code performs well on both OMAP and XScale CPUs (unlike Intel’s integrated performance primitives).  Luckily my previous performance testing of the multiply instructions helped guide me to save a few clock cycles off of several routines.  The purpose of this work is threefold:
1) I’m readying a new version of my imaging application (PQV - Pocket QuickView) for Windows Mobile and need it to be competitive with other products.  I pride myself on having the fastest viewer available.
2) I have been staring at the C code for a long time and wondering how much better it could perform if written in optimized ARM asm.
3)  I believe this code has value to anyone doing imaging or video on ARM based devices.  Web browsers, image viewers, camera applications, video players can all benefit from this code.

I’ve been searching for the past week or so for customers of this code, but the typical response is the “not invented here” attitude standing in the way of improving products.

I will post some sample images and benchmarks shortly to back up my claims of fast JPEG decoding.

Anyone interested in licensing object or source code should contact me directly (bitbank@pobox.com).