Sunday, December 09, 2007

Detecting the SDF file version

SDF files don't have an explicit way of letting you know their versions. What can you do to tell the version of a given SDF file? In my products I detect the SDF file version as a side effect of opening it: if a given engine can open that SDF file then I can safely assume it has the same version as the engine. This is not a very straightforward approach because it requires that you have all engines installed on the device (not a typical scenario).

The alternative way to detect the SDF file version is by reading a few signature bytes on the file. Just open the file, set the read location at offset 16 and read the 32 bit int there. The following values will tell you the file version:
2.0: 0x73616261
3.0: 0x002dd714
3.5: 0x00357b9d

I wrote a very simple .NET CF 2.0 application to illustrate this. The download link is this. If you find any SDF file that fails this test, please let me know.

Friday, December 07, 2007

WM6 GPSID problem workaround

John Spaith from Microsoft has blogged about a workaround solution to the HTC GPS problems on WM6. Apparently the size of the GPS_POSITION structure must be tweaked in order for the call to GPSGetPosition to work, but this can only be applied on devices where the first call returns 87... I actually worked around this by falling back to the COM port.

Monday, November 26, 2007

COM Port Enumeration

If you want to enumerate the available COM ports on your WM device, there is a very simple solution: look under the HKEY_LOCAL_MACHINE\Drivers\Active for all keys that have the Name value starting with the "COM" string. With some luck, you can even find a FriendlyName value under the key specified by the Key value.

The only problem with this very simple method is that it does not enumerate the Microsoft Bluetooth stack emulated COM ports. If you create a partnership with a device that has the serial port profile, you will be able to assign a free COM port to it. This COM port works like any regular serial port but does not show up in the list of active drivers on the registry. Microsoft decided to enumerate all Bluetooth virtual COM ports under HKEY_LOCAL_MACHINE\
Software\Microsoft\Bluetooth\Serial\Ports. To find all available COM ports you must enumerate all the child keys and look for the Port value under each key.

Interestingly, the Widcomm stack does put the virtual COM ports where they should be (or at least where I expected them to be).

Tuesday, November 20, 2007

VS2008 Install Heads Up

Before you install Visual studio 2008, make sure you read the readme file. There are two important implications for native and mobile developers: SQL CE 3.5 must be uninstalled prior to installinv VS2008 and the Windows Mobile 6 SDK will have to be uninstalled and reinstalled after installing VS2008.

Monday, November 19, 2007

VS2008 is out!

Check out the subscriber downloads in MSDN!

Thursday, November 15, 2007

Windows Live

Off-topic: Today I noticed that for the first time in the last few years Google is not on the top of the list of search engine referrals on my comany's site web log data. Out of the blue (or maybe not) Windows Live is leading the searches! This is intersting news for a chart that used to show a huge Google bar and essentially nothing else.

Monday, November 12, 2007

Performance Improvements in VS 2005

Jim Springfield has just posted in the Visual C++ Team Blog a very interesting piece of information: there is a new performance improvement QFE for Visual Studio 2005. This download addresses a number of performance issues and its features will roll over to VS 2008. I'm getting it right now to give it a spin.

Wednesday, November 07, 2007

Carousel Demo

Now that the carousel code is working correctly across a range of devices, I decided to upload it as a preview (download here). The code illustrates the carousel animation and user control as a strip on the child window of the WTL main frame. I'm still wondering how this "control" should be implemented, either as a "widget" on the main frame or as a toolbar-like control.

The main frame approach would implement the carousel code in the main frame allowing it to correctly resize the child window and even allowing the application to change the child view (like in a property sheet). With this approach it might also be easier to implement a means to change the location of the bar whan the screen is rotated. In fact, the carousel looks much nicer in a vertical position when you rotate your screen to landscape (right or left would be up to you).

Implementing this as a toolbar control would have the advantage of allowing the developer to reuse the code outside the main window, especially on dialogs and modified property sheets...

While I think about what to do, please do take a look at the code. The icons were "created" with Axialis IconWorkshop, one of the best icon editors around. Please note that these icons can only be used by registered users of the product and I'm not sure that you can reuse them on your applications.

Wednesday, October 31, 2007

GradientFill and a memory DC with a viewport

I’m working on a “carousel” control similar to the one you can find in the Yahoo Go! 2.0 application. This thing showed up in my HTC S620 WM6 upgrade and the control is very cool, so I decided to write my own implementation of it in C++ using WTL 8.0. The scrolling animation is achieved by painting to a memory DC and then blitting it to the screen. All went smoothly until I decided that the carousel background would look so much nicer with a gradient, making the center item stand out in a lighter background.

WTL 8.0 does a lot for you and I found myself having more work creating the icons for the sample than actually implementing the code... I started by using the CMemoryDC class which worked beautifully until I used GradientFill. All other GDI functions work correctly, but the gradient refused to appear correctly or at all. Interestingly, when the carousel strip was set at the top of the client window it would paint correctly, but would fail at the bottom.

Looking at CMemoryDC's source code I found that the constructor sets a viewport origin in order to cope with any rectangle. When setting the carousel strip at the top, the gradient would show up because the viewport origin would match the child window's (0,0), but fail when set to the bottom because the viewport origin would be different.

I ended up by using a slightly modified version of CMemoryDC, by removing the SetViewportOrg call on the constructor and zeroing the source bitmap coordinates at the destructor's BitBlt call. The carousel now works correctly on all four window edges (top, bottom, left and right).

Presently the carousel is implemented as a child view window but I'm looking at ways to make it work as a toolbar.

HTC P3300 GPS problems (again)

After posting in January about the failed implementation of COM events on the GPS port of the HTC P3300, I have another sad story to tell. After upgrading the device to Windows Mobile 6, the GPSGetPosition function always returns 87 (ERROR_INVALID_PARAMETER). There seems to be no appropriate set of parameters that this thing will take, you will always get back an error 87. Great! The GPSID on the P3300 is useless. The solution is to fall back to the COM port code...

Friday, October 26, 2007

Access 2007 woes

I don't have any complaints about using the Access 2007 application whatsoever. After the not so brief period that took me to learn the new user interface (some stuff on the older UI was quicker to use), the experience is quite smooth. Not so on the nuts-and-bolts side of the question.

As you already know I'm an OLEDB freak, and I use it for all native code database access I write both on the device and on the desktop. Last year I did write a sizeable amount of code for my data synchrnization component (Data Port Sync) and this targeted the JET 4.0 database engine. The code I wrote implemented both the Access database preparation and also change tracking. Database preparation involves creating a few extra tables and adding two columns to every tracked table. This looks pretty simple to do using straight SQL, but when I consistently failed to create self generating "replication id" columns (the SQL equivalent of the uniqueidentifier type with the rowguidcol property) I turned to the low-level
ITableDefinitionWithConstraints OLEDB interface to do all the table creation work. The code is not nice to see, but it is effective and gave me an added bonus: I can hide the tables from the user. To add the extra columns to the tracked tables, I used the
ITableDefinition interface.

Recently I started to get requests from my customers to support the new Access 2007 file format on my data transfer products. Changing the provider from Microsoft.Jet.OLEDB.4.0 to Microsoft.ACE.OLEDB.12.0 did the trick quite nicely because Microsoft kept all the other connection string properties untouched. BTW: where can I find a reference to all the properties and most importantly, where are the new header files for OLEDB?

The first implementation of the Access 2007 database engine was shipped on the Data Port Console release. Although it does not create the mdb or accdb files (yet), it successfully imports and exports data to and from the various SDF formats.

Going back to the desktop synchronization code (which will eventually see its way into the Console) I recently began to write a small desktop agent for simple desktop scenarios. Putting the new code to work was quite easy until I decided to test the code against an Access 2007 database. I picked up the old Northwind sample and converted it to the new engine only to find that my preparation code would fail miserably. There were no issues when the tracking columns were created, but it proved next to impossible to create the tracking tables: the engine would throw an E_FAIL error with a very strange OLEDB error description: "Could not find field." Period. I changed every possible factor that could be causing this: column names, the table name, absence or presence of delimiter brackets. Nothing would work. Out of desperation, I replaced the code with a straight SQL DDL command only to be greeted with a similar error: "Could not find field 'SID'." I beg your pardon? There is no 'SID' in my command! Has Access gone mad?

No, Access is working perfectly but the accdb file seems to be corrupt. After reverting all the code back to what it was, I decided to create a new accdb from scratch and then import new data from an SDF using the Console. After running it through the preparation code there was no error! Is the database conversion code broken in Access 2007?

Bottom line: don't convert mdb to accdb. Create a new accdb and then import the old data into it. Sigh.

Friday, October 19, 2007

The edit control under Windows Mobile 2003 and 5.0

After publishing my last article, I found out an interesting thing about the edit control on a Windows Mobile 2003 Pocket PC device: the up and down arrow keys behave differently from the edit control in Windows Mobile 5. In WM5, the single line edit control responds to the up and down navigation keys by setting the focus to the parent window. When this happens, the parent window receives the corresponding WM_KEYUP messages and thus is able to set up a navigation mechanism. Not so with the Windows Mobile 2003 edit control. This version of the control seems to "eat" these messages so the parent has no clue about the requested user navigation. This became quite apparent on my implementation of the CFormListCtrl: the navigation would not work.

This problem was quickly solved by adding the OnKeyDown message handler to the CCeEdit class and forcing the control to set the focus to the parent window whenever an up or down navigation keys are detected. Voilá!

Thursday, October 18, 2007

A list-based form for Windows Mobile

I have just published an article on CodeProject that better describes the list-based form control. As you can see from the article, I added a few other bells and whistles to the code.

Next two projects: port this thing to WTL and start writing an OLE DB class library for Windows Mobile. This second project is necessary because Microsoft no longer ships the atloledbcli.h file on the SDKs and this must mean something...

Thursday, October 11, 2007

Bug in the FormListSample

There is a bug in the FormListSample that causes a stack fault exception if you close the dialog with a created item control (edit, combo or date time). I'm looking at this right now.

Solution: On the CFormListCtrl::OnDestroy method, set the m_iEdit member variable to -1 after calling ShowEditor.

Meanwhile, I added some code to handle edit control resizing when the screen is rotated. The code can be found on the same location.

Monday, October 08, 2007

The list-based form control

Back in 2003 when the Smart Device Extensions were still in Beta and about to be renamed .NET Compact Framework, some people had to use C++ to develop database applications. I was one of these developers struggling with a crude set of tools: ADOCE for database access and the eVC3 dialog editor to design the user interfaces.

Soon we learned that ADOCE would be deprecated and so I started to look at the ATL OLE DB consumer templates. This is a great technology and I still fail to understand why it is not present on the WM5 and WM6 SDKs. In my code, I use an adapted version of the header file you get on the Pocket PC 2003 SDK but to be honest I don't like this approach (I will come back to this issue in a future post).

On the user interface side, we already had a very nice alternative to dialogs: the list-based form control used by the Pocket Outlook Contacts application. Not only this is an intuitive control for the user, it also promised to be easy for a developer to use: no designer needed to be involved, you just specified the list of items to edit and fired the object.

The big problem with this control was that there was no API for it so I had to write one. Back then I was using MFC big time due to the compiler support for it on eVC3 and eVC4. Now I am not so sure that MFC is a good option for native user interfaces and I'm leaning towards WTL. You now have great tool support in VS 2005 with the WTL Helper tool which I am using on a daily basis and with great results.

So I eventually wrote an MFC control to implement a list-based form and in the process I threw in couple of goodies such as grouping, context menus for managing the items, control notifications and a few other bells and whistles. After a recent request of fellow MVP Christian Forsberg for a similar control, I decided to go back to my 4 year old code, adapt it to VS 2005 and publish it. I had to do more work than expected because nowadays there are lots of devices that have a keyboard, display in landscape and even have VGA screens! Back then I was used to portrait QVGA screens and no keyboard, so some changes were in order.

Before I publish this code as an article, I decided to preview it here so you get a chance to look at it and let me know what you think. Download FormListSample.zip

Thursday, September 20, 2007

Supporting SQL Compact 3.5

Native code is so cool! As of today I can write applications that target SQL CE 2.0, 3.0 and the new 3.5 Beta 2. The trick? Extend this technique to the SQL Compact 3.5 header files. Microsoft made our life really easy by making very small changes to the header file, so you only need to copy the definition of CLSID_SQLSERVERCE_3_5 and all the property definitions of
DBPROP_SSCE_DBENCRYPTIONMODE. Now your header file can be used for 2.0, 3.0 and 3.5!

What this means for me is that SQL Compact 3.5 will be supported by the release version of Data Port Console and I will also issue a last version of DesktopSqlCe that will also support the new database engine. This will be the only game in town for .NET 2.0 desktop applications that must support both the 3.0 and the 3.5 database formats (without code changes, of course).

Cool!

Friday, September 07, 2007

SQL Compact 3.5 Beta 2 and VS2005

Ready to move forward and add SQL Compact 3.5 support to my products, I downloaded the Beta 2 bits in the hope to find the required header files. Unfortunately they were nowhere to be found. Does that mean that you cannot use VS2005 with SQL Compact 3.5 Beta 2? No. Fortunately there is an indirect way to get the much-needed header files: download and install either Orcas Beta 2 (not yet for me) or Microsoft Visual C# 2008 Express Edition Beta 2. Apparently the header files are also available on the Visual Basic edition.

Now back to work.

Friday, August 31, 2007

Database Diagrams for Data Port Console

The second release candidate of Data Port Console 1.0 is almost out and while I was removing some bugs, I failed to resist the urge to bring back some code that had been sleeping for amost one year: database diagrams. Yes, coding should also be fun so I decided to add this to the 1.0 and in this post I'm offering my readers the chance to try this new feature. You can create multiple diagrams per database and now all information is persisted as an XML file instead of using the registry. You will also notice that there is a new folder for tables and that you can group them by their first letter. Please let me know what you think about these new features while RC2 is not uploaded to the site. Grab your copy of this interim build here.

Tuesday, August 21, 2007

ZIP and RAPI - The article

My latest musings on this subject have been published on CodeProject. Read the article here.

Sunday, August 19, 2007

ZIP and RAPI - Yes, it's faster

I really was not pleased with the performance results I got from the RAPI Unzip extension I published in my last post. My reasoning was that if you send a compressed data stream to a device and decompress it you should get a better performance than decompressing the data on the PC and sending it to the device. The results I got were not very satisfying: the RAPI extension DLL was not clearly faster than the PC decompression, especially for ZIP files with small compression rates.

So I decided to take a harder look at the code and found the culprit: WriteFile latency. The function was being called way too often and sometimes with small sets of data. If you look at the code, you will see that WriteFile is called when either the decompression input or output buffers are emptied. This is wrong. The call must only be made when the output buffer is empty and not when the input buffer is. When the input buffer is emptied it must be refilled from the RAPI stream and the output buffer should not be flushed, otherwise we risk flushing a small amout of data expending one WriteFile call.

The final result is now ready and is consistently faster than the PC decompression approach. Try it!

Friday, August 17, 2007

ZIP and RAPI - Is it worth it?

After a few more days working on Lucian Wischik's Zip Utils code I finally managed to build a working RAPI ZIP decompression server. The architecture of this RAPI extension is quite simple: it exports a single method (ZipServer) that implements a streamed RAPI call. Streaming (non-blocking) RAPI calls are very nice because they allow you to keep an open connection with the desktop which is especially useful when expanding very large compressed files: you can slice the compressed stream and have it decompress on the device. For more implementation details please see the source VS 2005 project in the above link.

To make this work I changed the CeUnzip project in order to support calling a RAPI extension and added an extra mandatory command line argument: -i for expanding on the PC from a ZIP file on the device and -e for the exact opposite operation. It's here that I make the remote call to the RAPI extension DLL. Please note that the two projects use different versions of the unzip.cpp file. I will correct this before publishing an article that describes in greater detail the inner workings of the code.

How about results? Is this really faster than using an on-the-fly decompression algorithm on the PC and using CeWriteFile to write the decompressed data on the device?

My first results were very disappointing. When compared to an installer application I wrote for a customer that decompresses on the PC and writes to the device, I consistently got worse timings. The only remedy that made the device DLL run as fast as the PC was to increase the IRAPIStream read buffer size to 128 or 256 KB. As a matter of fact, RAPI read latency is a big issue here. Before giving up I looked at the particular ZIP file I was using to test: it was quite large and had a relatively small compression ratio. Maybe this explains something?

My next test was to use a very high compression ratio ZIP file and run the same tests (expanding it to the device using the two different approaces). This ZIP file was built from a very large SDF file which almost disappeared when compressed: 193 KB to only 3 KB. Now the results were a bit different...

Depending on the device, the DLL expansion was from 2 to 4.5 times faster than the PC's. This means that for compression ratios closer to 1 it is (almost) indifferent which approach to use, but when the ZIP compression ratios get larger, it's far better to use the server DLL.

Sunday, August 12, 2007

ZIP and RAPI

For quite sometime I have used Lucian Wischik's Zip Utils, a set of zipping and unzipping functions that work very well both under Win32 and Windows CE. This code has allowed me to do a lot of fun stuff both on the desktop (specialized installers) and on devices (an HTML browser for ZIP files).

Recently I had to use this code to write a specialized device installer (no cabs) for a consumer application that runs on all sorts of devices. This installer was designed to extract files from a ZIP on the desktop and copy the extracted files to the device over an ActiveSync connection. I used Zip Utils to extract the data and RAPI to copy the expanded files to the device. This works but can be slow on some devices. Wouldn't it be great if I could expand the files on the device while having the source ZIP file on the PC? I would surely make the whole thing faster because the RAPI transport times are a big bottleneck in this whole process.

Due to time constraints, the installer is now shipping like this: data is expanded on the PC and copied to the device. Now I'm starting to write an application that will update the device code and data. Interestingly most of the static data is stored on ZIP files on the device and the updater must extract specific files on the ZIPs in order to know some details. The problem is that some of these ZIP files are over 2 MB and copying them to the PC just to extract one tiny file is out of the question due to slow transfer times.

No options here: I had to roll up my sleeves and started to read Lucien's code in order to see what could be done. This was no walk in the park because he uses a very packed code indentation, and understanding the code was not easy at first. Then I noted that all the ZIP file access methods were neatly encapsulated in specific functions (like lufopen, lufread and so on) so it would be quite easy to replace the desktop file access functions with RAPI's.

My approach was to expand the LUFILE structure and include a set of function pointers that would be initialized with the regular API when the ZIP file is on the PC and with RAPI's when the ZIP file is on the device. After 20 minutes the code was working and I was able to write a very simple command line unzipper (get the code here).

Now I want to solve the first problem I had: efficiently unzipping a file to a CE device. This will require a RAPI DLL on the device that will have all the decompression code. When this is ready I will publish the results in an article. Stay tuned.

Friday, August 03, 2007

Bitten by the desktop GC

If you downloaded the Console Beta 4 I published yesterday, you might have noticed how badly it bombed when exporting an SDF database to Access. The error message you see usually means that some native code DLL is writing to NULL pointers or doing some other equally responsible stuff. In this case what you see is a NULL pointer dereference (yes, that bad).

While running perfectly in Debug mode, the error almost always showed up in Release mode. When exporting very short databases or single tables it might not show up. But when I tried to export the Northwind sample the Console would bomb exporting one of the largest tables (Order Details or Orders). The keyword here is random because as it turned out, the error was being caused by the garbage collector (well, my bad code was causing it - the GC just made it apparent).

The Access database code was implemented in C++ with a similar approach as DesktopSqlCe's low-level classes: there are separate classes for the table structure and the table cursor. In order to open a base table cursor and insert data on the table (no SQL is used for data manipulation) the code creates a table object and "opens" it returning a "rowset" object. My mistake was to have the table class include an ATL CTable-derived object, not a pointer to it. The CTable-derived class contains all the accessor and rowset logic that are used by the rowset object. Making it static is a bad idea because the desktop .NET GC did not know about this and kills the table object because it thinks it is no longer needed. After all the only active object is the rowset... Now you see the problem: by killing the table, the rowset is implicitly killed as well because it shares an object that is statically owned by the table. Closing the rowset means that a few internal pointers will be deleted and set to NULL. Bang! Am I smart or what? (The answer is "No").

I uploaded a revised Beta 4 that solves this issue, so if you installed the one I uploaded yesterday please replace it with the new one.

Thursday, August 02, 2007

Data Port Console 1.0 Beta 4 available for download

I have just uploaded the new Data Port Console Beta 4. As previously promised, import and export to Microsoft Access (2002-2003 and 2007) is now supported and this looks like it will be the last Beta. Now I will focus on cleaning a few bugs and will try to have the final version 1.0 by mid-August.

What's next? Primeworks.Data - the merger between DesktopSqlCe and Data Port Sync with a few "benefits" such as the ability to make P2P connections via Bluetooth or WiFi between two devices. Also I will add support for the JET (ACE) engines on the desktop server and will publish the services via a muti-threaded Windows Sockets server (I don't anticipate the need for IOCP anytime soon because there will be few concurrent connections).

The new Beta 4 can be downloaded from here.

Monday, July 30, 2007

Bluetooth Service Publishing

The code for my forthcoming article on Microsoft Bluetooth Stack inquiry and discovery (remember, inquiry is for devices and discovery is for services) is ready. Apart from inquiring the available devices, it also discovers the existing services and lists the SDP record contents.

After being able to find a device with the service you want to consume, you can connect to that device using Windows Sockets. The reverse process involves publishing a service for other devices to consume and to serve requests using WS. Unfortunately the SDK has no means (nor explanation) on how to create an SDP record. Platform Builder users have the BTHNSCREATE sample to play with, but what about us, mere SDK users? Looks like Microsoft thinks this is something that should only concern people designing new Windows CE or Windows Mobile devices. I sincerely hope not and I'd rather think this is a design oversight. Why would I need such a thing?

Well, one of my plans is to provide P2P support for my products. If you look around the newsgroups you will see lots of people asking for an SDF-only synchronization package. This will require that two SDF files can "talk" to one another. I already support having a PC talk to an SDF file on a device, but what about having one device talk to another? A year ago I actually achieved this using WiFi, but this is not the correct protocol for ad-hoc P2P scenarios - Bluetooth is better. So if I want to support this scenario, I must publish a new Bluetooth service. Yes, of course I could use emulated COM ports and the code already supports serial communications. But I want the real thing: a dedicated service with its own GUID.

So how am I going to circumvent this? Most likely I will use Doug Boling's solution: use a templated SDP record and fill in the gaps (not nice, I know). What really bugs me is that the Widcomm stack makes it so much easier to publish a new service...

Wednesday, July 25, 2007

SHMENUBAR and MF_GRAYED

My WTL 8.0 experience with Windows Mobile development is going just great. The application wizard worked out correctly with only a very minor issue: the WTL include directory is not set up either for C++ compilation nor for resource compilation. As I said, this is a minor issue that you overcome quite easily.

While working for the new Microsoft Bluetooth device inquiry and service discovery (these seem to be the appropriate Bluetooth terms) I found out that Sergey Solozhentsev's WTL Helper tool works like a charm in Windows Mobile projects under VS 2005. All of the message handling functions for the main frame window were generated with this tool and it makes it very easy to write all the UI code - this tool just rocks.

Today I found out about something that does not seem to be documented anywhere: when using the SHMENUBAR resource, never specify a menu resource with a grayed (MF_GRAYED) menu item - the menu will not show up. The WTL code is very straight forward and uses the SHCreateMenuBar API, so this was not where the problem lied. After removing the grayed style from the resource editor the menu magically showed up! So is this a bug on the shell or on the compiler?

Monday, July 23, 2007

Back to Bluetooth the WTL way

I'm writing this post from (today not so) sunny Algarve using my brand-new Vodafone Mobile connect card. This thing really works but the Vista version of the software seems to be a bit slow when booting. Also, if I boot the machine with the card plugged in the driver will not find it. Apart from this it's a treat - I get internet access pretty much wherever I want to (coverage permitting).

I'm coming back to writing about Bluetooth on Windows Mobile devices and this time I'm exploring the Microsoft stack. Using MFC code I had written almost a year ago, I'm now turning to WTL to rewrite the sample for the article. So far I can tell you that the Windows Mobile WTL wizard looks quite competent at generating the basic application code. More impressions on this experience will be published here. Stay tuned.

Tuesday, July 03, 2007

CeGetDiskFreeSpaceEx - II

This is not an ActiveSync issue: my iPAQ 2210 does not support this API nor do some Windows CE 5.0-based GPS devices I've been working with. At the end of the day, I had to write a RAPI DLL to support this. The code is quite simple:

typedef struct _DISKSPACE
{
ULARGE_INTEGER uliFreeUser,
uliTotalSize,
uliTotalFree;
} DISKSPACE;

__declspec(dllexport)
int DevGetDiskFreeSpace(DWORD cbInput, BYTE* pInput,
DWORD* pcbOutput, BYTE** ppOutput,
LPVOID pReserved)
{
DISKSPACE ds;
BOOL bOk;

bOk = GetDiskFreeSpaceEx((LPCTSTR)pInput, &ds.uliFreeUser,
&ds.uliTotalSize, &ds.uliTotalFree);
if(bOk)
{
*ppOutput = (BYTE*)LocalAlloc(LPTR, sizeof(ds));
memcpy(*ppOutput, &ds, sizeof(ds));
*pcbOutput = sizeof(ds);
}

return 0;
}


Of course, you need to put this in a device DLL and consume it as a blocking RAPI call.

Friday, June 29, 2007

CeGetDiskFreeSpaceEx

This is one of the cases where you do have to dig into the SDK header files to find what you need. The CeGetDiskFreeSpaceEx RAPI function is not documented on my VS2005 MSDN, although you can easily find it on the online MSDN. I have to confess that I only found it after looking into the Windows Mobile 5 Pocket PC SDK rapi.h file. The online documentation says it is available since Windows CE 3.0, but a quick look at the same header file on the Pocket PC 2003 SDK is enough to see it is not there. So how do we decide who is right, the docs or the header? The answer is simple: use dynamic linking to the rapi.dll, and you will find out if this is supported or not.

During my furious searches on the net, I found an obscure thread posted by someone from Microsoft stating that this API is only exposed from ActiveSync versions 4.0 onwards.

Tuesday, June 26, 2007

Data Port Console 1.0 Beta 3 available for download

Right after uploading the Data Port Console Beta 3 (*), I decided to implement the TCP/IP sockets connectivity feature you could use in the old SQL CE Console. Extending the code was easy enough and I was able to do something that was impossible with the old code: connect to more than one PDA at the same time. This is going to enable some interesting scenarios where just one console will be able to manage mutiple PDAs connected to the desktop via a network. For GPRS scenarios this may need a mobile VPN to fix the device IP address. I've been thinking on how to go around it seems that the only way is to somehow revert the PDA and PC roles to a somewhat more "natural" way where the PC is the server and the PDA is the client, and not the other way around.

Next up is to enable the serial port connectivity for Bluetooth emulated COM ports (the code is there, just needs a little work). I would like to have a native Bluetooth connectivity option in order to make it simpler for users to set up their devices, but this will imply going back to my Bluetooth code (which I started to write for this very purpose...).

Where do I want to go last? Device P2P. In a few days I will start working on the DesktopSqlCe successor that will also run on devices, so your mobile applications will be able to consume SQL Compact Edition databases locally or on a nearby device.

Back to work.

(*) This is not a real Beta. I will keep adding features to the application while it is almost ready to go live and after that as well. Beta status will stop when data can be exported to an Access database and when the number of errors is reduced to a sane minimum.

Monday, June 25, 2007

Primary Key or Index? ROWGUIDCOL or Guid.NewGuid()?

If you are really worried about the performance of your SQL Compact Edition database, switch all your primary keys for unique indexes and always let the engine generate the UNIQUEINDENTIFIER's GUID value through the ROWGUIDCOL property - never ever use the Guid.NewGuid() function.

Looking for more performance material to publish about SQL Compact Edition, I found myself testing the performance of GUIDs when inserting on an indexed table. Performance will be marginally slower when you insert a GUID on a PRIMARY KEY column than when inserting it on a UNIQUE INDEX. In a 10,000 row insert sample it can be as low as half a second, but nevertheless this is an interesting result: PKs are slower.

Now, if you remove the ROWGUIDCOL property from the UNIQUEIDENTIFIER column and start generating the GUID values yourself, be prepared for a big surprise: the insertion time tripled (10.5 to 30.7 seconds on my battle-scarred JasJar). Is the Guid.NewGuid() function that slow?

Change MSI name in VS2005

Why can't we change the MSI file name on a VS2005 deployment project? When you create a deployment project with VS2005, the name of the resulting MSI file is the same as the project's name. From this point on, there is no way to change the output file name from the project properties (nor from anywhere else on the IDE, or is there?). Even if you rename the project on the Solution Explorer tree, the resulting MSI file name will not change.

The solution for this is to manually open the .vdproj file and edit it on a regular text editor (Notepad will do). Now search for the "OutputFilename" string under the configuration name of your choice (by default you will see "Debug" and "Release" under the "Configurations" group, but your project may have other configurations), and change the MSI file name. Save the file, open the project in VS2005 and rebuild.

Request for Orcas: can Microsoft please make this property available on the IDE?

EDIT: Someone smarter than me just showed me the way... Thanks, Pedro!

Tuesday, June 12, 2007

More troubles installing WTL Wizards in Vista

WTL 8.0 is out now so I decided to install it on my Vista box. Now that I know a bit more about Vista security, I launched a command window in Administrator mode in order to run all the setup scripts (desktop, Windows CE and Windows Mobile). All went smoothly.

Then I decided to install Sergey Solozhentsev's WTL Helper tool. No issues again (nice!). This great tool requires that you download and install a new WTL Wizard from Sergey's website. Instead for using a JScript file to install everything, Sergey's Wizard uses an MSI file, and this is when I felt the iron grip of Vista security again: the MSI just would not install reporting an error number 2739. My friend Google pointed me in the right direction, first to understand what this error means, and what to do about it.

For your information, I did not remove the JScript key but merely renamed it. Running the msiexec /i command from the admin command window did the rest of the trick.

Friday, June 08, 2007

Data Port Console 1.0 Beta 2 available for download

You can get the latest Beta 2 from this link. There are a number of bug fixes in this Beta that make it more stable and reliable. Error reporting has been improved but this requires that you update the device component using the included installer. As a matter of fact, users would be greeted with empty error dialogs because of how the OLE DB error information was being collected.

One of the features I added for this Beta was a special request of Alberto Silva: the ability to edit the query data grid (when the user enters an "updatable" SELECT). Behind the scenes, the code just uses a SqlCeCommandBuilder to create the necessary commands (displayed on the notes tab) and these are used for updating (use the save button). You can also filter the grid by selecting the row state and the changes can be rolled back row by row (before updating, of course).

Comments and suggestions are welcome!

Monday, June 04, 2007

Tuning SQL Compact Edition Insert Performance

Here's how you can improve on a good thing: speed up your bulk insertions in SQL Compact Edition up to 30%! Read all about it here.

Wednesday, May 30, 2007

DBPROP_SSCE_MAXBUFFERSIZE

Looking for ways to make batch insert work faster under OLE DB, I tried to fiddle a bit with the SQL CE 3.1 database properties. My first approach was to radically increase the maximum buffer size to 2 MB using the DBPROP_SSCE_MAXBUFFERSIZE property. The early experiments look promising with speed performance increases in the 50% range (yes, that much). I promise to come back to you with a better case in the form of an article where I will compare insertion performance under different scenarios and property settings.

For now, keep this in your mind: increasing the value of DBPROP_SSCE_MAXBUFFERSIZE may actually help your database perform better.

Sunday, May 27, 2007

MFC Revisited

A few weeks ago, Mike Hall posted about "Why use MFC on Windows CE?" This was a bit of a surprise to me because you hardly see Microsoft discussing MFC these days. When the Compact Framework was launched, native code got such a bad press that I thought Microsoft was about to kill its C++ developer base. Fortunately I was wrong.

I (re)started developing for mobile devices in MFC and that was a very interesting experience. In those days the best PDA around was a Compaq iPAQ 3870 with Bluetooth and your development environment of chioce was eVC3. MFC seemed to be an obvious choice due to tool support but there were a few shortcomings. The frameworks imposes a document-view model that sometimes you have to fight against. Documentation was scarce (yes, the online help was bad) and your best resource was to read the MFC source files. This was how I got to understand how the framework was designed and why the tap-and-hold always made the dots circle twice. Interestingly you can see this behavior in a lot of the most recent devices on the Settings applets meaning that these are written in MFC (and the double circling bug is still there - sigh).

There is one good reason why you should not use MFC: it is slow. I understood this when I was working on the SqlCeSpy code and found that MFC would refresh a virtual list view noticeably slower than other applications, especially the ones written in ATL. MFC's message handling mechanism is a bit complex and convoluted meaning that when you need to handle a reflected message it gets bounced back and forth before it actually gets to where it is needed. The result for me was a slow refresh of the virtual list view. So slow in fact that it prompted me to write a grid-like control using virtual methods instead of reflected notification messages. Come to think of it, I never published this code...

So what is the best choice? As far as I can tell, when handling a user interface in native code, your best choice is to use WTL, ATL's extension now freely available from sourceforge. The thunk mechanism for handling the message maps make it very fast and efficient to process windows messages and applications tend to be both faster and smaller (compared to the statically linked MFC applications). Also, you feel like having much better control of what is going on and the templated approach is very elegant, although it requires conquering a steeper learning curve. But once you're there, you're hooked.

Thursday, May 24, 2007

Installing the WTL 7.5 Application Wizards in VS 2005 under Vista

Don't even try to use the install script: it will not work. Vista's security mechanisms prevent the script from doing anythig on your VS 2005 install directories. I just went through this situation this morning and realized there was just one way to go about it: manually.

It's not that difficult, but took some time to reverse-engineer what the script was doing. The first thing you need to do is to locate the VS application wizards directory. In my case it's in:

C:\Program Files\Microsoft Visual Studio 8\VC\vcprojects

Under this directory you must create a new one named WTL (what else?). Now go to the directory where you installed the WTL 7.5 files and copy the following files:

WTLAppWiz.ico
WTLAppWiz.vsz

to the vcprojects directory. You will need administrator clearance to do this. Now change the security settings of WTLAppWiz.vsz to allow editing. Change it so it looks like this:

VSWIZARD 7.0
Wizard=VsWizard.VsWizardEngine.8.0
Param="WIZARD_NAME = WTLAppWiz"

Param="WIZARD_VERSION = 8.0"
Param="ABSOLUTE_PATH = D:\src\WTL75\AppWiz\Files"
Param="FALLBACK_LCID = 1033"

Replace the D: path with your own WTL 7.5 directory. Finally, copy the WTLAppWiz.vsdir file to the WTL directory you created before and, going through the same security checks you did for the vsz file, change it so it reads:

..\WTLAppWiz.vsz ATL/WTL Application Wizard1An application that uses the Windows Template Library. 67774096#1154

You are done.

Tuesday, May 22, 2007

Data Port Console 1.0 Beta 1 available for download

I have just uploaded the Data Port Console 1.0 Beta 1 setup file. This is the first public Beta of the product and it already has the license mechanism in place, limiting the use to 30 days. For the people I promised to offer a free license, now is the time to collect it: please send me an email with your desired license name so I can issue the key.

There are some new features wothy of notice:
  • Connection breakups are detected and handled. This means that if you inadvertently break the USB connection both the desktop and the device will gracefully recover (the device may take a few seconds before it becomes responsive, but this is a RAPI issue).
  • The device component is now manually installed from a specific menu. I have included a very comprehensive set of device cabs: Pocket PC 2003, Windows Mobile 5 (both Pocket PC and Smartphone), Windows CE 4.2 (all CPUs) and Windows CE 5.0 (all CPUs). Hopefully the WM5 cab will install correctly on WM6 devices.
  • The new version of DesktopSqlCe (1.8) is included (the console is built on top of DesktopSqlCe 1.8) and the Gold will ship with a single user license of this component. This means that if you just want to use the component in one PC (the same where the Console is installed) you will not have to pay the extra DesktopSqlCe license.

I'm really interested in reading your opinions on this product and what features you would add / remove / change.

Sunday, May 20, 2007

Diagnosing cab installations

This is an old time favorite but I seem to keep forgetting it. So for my future reference, here are the registry keys for enabling cab installation diagnostics on the PC:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows CE Services\AppMgr\ReportErrors = (DWORD)1

Thursday, May 17, 2007

The dangers of not terminating your strings

After a bit of a long break I'm here to tell you about my latest wild bug hunt. A few months ago I was contacted by a French company to develop a high-speed text to SQL CE converter. This component allows the user to send plain or compressed text files to a device and locally process inserts, updates and deletes. Due to its very nature, the code was supposed to accept either UTF8 or UTF16 character encodings.

My first approach was to use the text conversion functions (wcstombs and mbstowcs). This way I had only one set of conversion functions (I mean converting from text to a GUID, to a DBTIMESTAMP and so forth). After the first tests the customer complained about stability: the data would be written to the database but the component DLL crashed almost consistently.

Back to the eVC4 debugger (now running on my Vista box in a Parallels virtual machine) I was confronted with an ugly beast. After successfully running the code, the whole thing would blast into hyperspace when closing the data source object (yes, that's the last thing you close). Hunting the bug forced me to look everywhere (even in the tested ATL OLE DB code). The thing was nowhere to be found. Often times I had to hard reset the debug device in order to get it back to its feet. Not a nice thing...

Bugs like these "smell" like memory issues: you write to a wild pointer and you may destroy some very fundamental data structures in your application. Needless to say that you are in for some unexpected outcomes.

I did not kill the bug directly. Instead, I rewrote the code so as to avoid text conversions. After running the new code for the first time the whole thing just behaved correctly. So should we avoid the text conversion functions altogether? Absolutely not! Just be wiser than me when you use them and make sure the converted strings are terminated. An unterminated string may cause this kind of problems in your application. So beware: you can either add one to the source string length or you can do that to the target string and make sure the buffer is zeroed before the conversion. Or you can do both.

Saturday, April 21, 2007

What was the last inserted IDENTITY value?

One of the nice things you get from using OLE DB is that you can readily access the last inserted IDENTITY value without resorting to the funny @@IDENTITY. You just insert the new row and read back the inserted value - it's that simple. If you use the .NET CF 2.0 ADO .NET provider for SQL CE 3.0 you can also use a similar technique. Read all about it here.

Wednesday, April 11, 2007

Installing CAB files from desktop .NET

Data Port Console is now on Draft 15 and I decided to move ahead and promote it to Beta. There are still lots of features that I will add in the future (both during Beta and after the product goes "gold"), but there was one on the top of my list that had to be done right away: installing the device server from within the application. This is actually quite necessary for Windows Mobile 5 devices (both Pocket PC and Smartphone) because the installer CAB not only deploys the required DLL but also enables RAPI connectivity.

The code I wrote for the installer is quite simple and I decided to write a short article on this. You can read it here.

Monday, April 09, 2007

Who put SQL CE 3.1 in my C:\Windows\System32?

I have this one to figure out. My brand new Vista Ultimate box has a mysterious version of SQL CE 3.1 installed in C:\Windows\System32 that is referred to by the registry as:

Microsoft.SQLLITE.MOBILE.OLEDB.3.0

Say what!?!? SQLLITE???

P.S.: Yes, it looks like it is causing trouble: IAlterIndex does not work in my PC even after reinstalling SQL Compact Edition 3.1...

Saturday, March 24, 2007

SQL Compact Edition Insert Performance

How fast can you insert on a SQL Compact Edition database? On March 22nd I delivered a presentation on SQL Compact Edition in the local TechDays 2007 event. The event was a great success with lots of people literally flooding the venue. Unlike Alberto Silva, I was lucky enough to present only once. Poor Alberto had to make the same presentation twice due to the unbelievably large number of people that attended his first show. I managed to get away with a peak audience of 167...

The demo that caused most impact on my presentation was a benchmark between four different approaches to bulk data insertion on a SQL Compact Edition database. As you are probably guessing, using native code and OLE DB was the fastest scenario but the SqlCeResultSet also puts out a very decent performance.

To better illustrate this (and also to release the code to the public), I published an article that explains the benchmark and shows how wrong you can be if you don't use the correct approach...

Sunday, February 25, 2007

The Bluetooth sources

When I wrote my first article on the Widcomm Bluetooth stack, I promised to publish a .NET CF 2.0 library that would abstract the enumeration features of the Widcomm and Microsoft stacks under a unique API. My life became very busy since then, especially when I got a contract for integrating the new version of a mobile GPS application on the Windows Mobile environment. This has been a very interesting challenge that has put all my knowledge through its paces and made me learn a lot: powering off the device, integrating DirectDraw with screen rotations, popping up the phone when a call comes through and the screen is in DirectDraw mode, handling bizzare GPS behaviors, exotic device keys (think HTC 3300)... The works!

Requests for the Bluetooth code and article have not stopped, though so I decided to post links to the unedited versions of the C++ and C# sources. Before I get to fully comment the code and write a proper article, what you see is what you get. The sources are divided into 3 ZIP files:

Bluetooth.zip - Contains a sample C# WM5 application that enumerates devices and services. Also contains the Primeworks.Bluetooth class library.
msbts.zip - The low-level Microsoft Bluetooth stack wrapper.
wcbts.zip - The low-level Widcomm Bluetooth stack wrapper.

Now, I can take my time and write the full length article. All your comments and suggestions are welcome.

Sunday, February 18, 2007

Handling the Power Button

After three months without writing, I posted today a new article named Handling the Power Off Button. This reflects my recent experiences on managing the Pocket PC resources when the power status changes.

I finally got the eToken from Verisign. From now on I will be able to digitally sign my device DLL and CAB files in order to make life so much easier for my customers. I hope to have the first CAB for Windows Mobile 5 (Pocket PC) out next week.

Monday, February 05, 2007

An unexpectedly good experience

I always hated the idea that Windows Mobile code needs to be signed to properly run on our beloved devices. And I also admit that I have resisted to signing my own code, maybe in a stubborn or lazy way. Signing your code is an expensive thing and I was fearing that it would also be a burdensome and expensive bureaucratic process, so I was delaying the decision to bite the bullet as much as I could.

Well, I have to admit that I wasted a lot of my time procrastinating... After contacting Verisign for the first time on January the 31st, I got the full approval today. Instead of a heavy bureaucratic process, I was only asked for a telephone bill copy. After emailing it last Friday, I got the approval early this morning.

This is still not an inexpensive service, but it certainly is easy to purchase!

Tuesday, January 30, 2007

Installing a CE MAPI filter

We all know how this is done, right? We start by installing the CE MAPI filter DLL on the device (must be signed for WM5 devices), we register it and we restart the messaging application. Hum... How do we restart the messaging application? My approach (and I have to say it is not only my approach because I see it a lot) is to soft-reset the device. Not bad for a Pocket PC 2003, but a nuisance for a WM5 device - it just takes too long to reboot. Needless to say, this approach is a nightmare for developers trying to debug a CE MAPI filter DLL: you have to restart the device twice for each deployment (registering and unregistering the DLL).

There is a better way, though: the messaging application can be closed with a simple WM_CLOSE message sent to the right window. To find that window, use the FindWindow API with the "Inbox.MainWnd" class name. Once you close the messaging application, you can register and unregister the DLL without resetting the device. Nice.

Wednesday, January 24, 2007

Read-only SDF files

Ever tried opening a read-only SDF file? The OLE DB provider will refuse to open it, reporting error number 25039 (SSCE_M_FILEACCESSDENIED): "Access to the database file not allowed". The workaround for this is to provide a writeable path for the temporary files directory on the connection string (or connection properties). Thanks for this piece of info, Laxmi!

Friday, January 19, 2007

Reading the GPS port on the HTC P3300

So how do you read a COM port? After a few years of practice I got the impression that using WaitCommEvent on a thread was an assured way of catching all the characters sent by the serial port. As a matter of fact I have used the same code over and over again with the same reliable results, whether I was reading a real serial port or an emulated one over a Bluetooth connection.

Recently I had to tackle the built-in GPS serial port of the HTC P3300 and got a big surprise: my code wouldn't work! In fact, no characters were being buffered by the thread code meaning that the consuming application was receiving no data... After a close examination of what was going on in the thread code, I realised that no events were being generated by the serial port, namely the EV_RXCHAR that is used to signal that the serial port has characters to deliver. Interestingly, if you use the ReadFile API with a reasonable set ot timeouts you will be able to read data.

It is baffling to se how unreliably hardware support for common stuff like serial ports can be implemented. I'm still trying to figure out why HTC implemented it this way...

Friday, January 12, 2007

Recognition

It's nice when you see your (modest) offline help publicly recognized. Thanks for this, Maurizio!

Time to update eVC4?

I'm getting a few weird 0x80000002 exceptions in my eVC4-generated code. After looking around, it looks like this *may* be a compiler issue. Microsoft has provided an update to address this. I wil try it out and post back the results.

[Edit]
Well, this was *my* error, not eVC4's... Shame on me.

Friday, January 05, 2007

RAPI Data Throttling

One of the significant changes of Windows Mobile 5 devices over the previous generation was the noticeable speedup of RAPI communications. My iPAQ 2210 just crawls when compared to the either the JasJar or the K-Jam (with a slower CPU). This means that it is much easier for me to test my remote database access code on the WM5 devices, but I still keep my pledge to support older devices like my pre-historic iPAQ 3850 with the Pocket PC 2002 OS. And this means slower RAPI connections.

The connection speed can be so slow to the point where loading a very large table from the iPAQ 2210 (on a CF card) to the new Console may take several minutes. In the case of the huge table I discussed before, this means a 15 minute load time. If you think like I do, this is unnacceptable. So how can we speed up the communication between the device and the desktop? Easy: ZIP it!

In my particular case this was quite easy. All of my remote database access products use the same device DLL that communicates with the desktop via RAPI, TCP/IP or even the serial port. Data is packaged in messages of varying sizes and, depending on their semantics, they are either dispatched immediately or grouped together in a 64 KB buffer and sent when it fills up. This seems to be the optimal size for RAPI connections (according to one slide deck from MEDC 2005). So what happens if you compress this buffer before sending it? In my case the data transfer time was cut to a third. Now the behemoth table downloads to the desktop in under 5 minutes.

Finally, the ZIP library I'm using was found in CodeProject. This code allows me to compress and uncompress to a memory buffer, making it perfect for my own purposes.

Tuesday, January 02, 2007