Fix sending graphics to Zebra Thermal Printer with GW command -corrupts images

Attempting to print from the RPi over serial RS232 interface using the GW command, I was getting image corruption. Some of the image would appear to wrap, or the image would just not print unless some extra line feeds were added to the end of the command. This was even though the number of bytes sent was correct.

After blaming my code for dithering the image for three hours, I finally found the issue. I had checked through each printer software switch and setting, wasting much time tinkering with form size, thinking it was the cause of picture wrapping. I finally looked at Windows Mode (notice how W is towards back of the book). This was set to Y (YES), looking at the description in the EPL programming guide, it said it all…

The Windows mode escape sequences are only used by the optional Windows printer driver. When working with a main frame or other non-Windows host, this mode can be disabled to prevent erratic operation.

As I was using RS232 on Windows IoT core – I think this counts as requiring a setting of “NO”.

So sending the EPL command “WN” did the trick. No more odd behaviour sending the binary for the PCX image. I’ve seen on many forums other people struggling and giving up on sending images via GW, hopefully this post may give some another thing to check. Do comment if it helped you!

Upgrading GP Addin Mods to use EF6

After adding the configuration sections to Dynamics.exe.config

<section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
<defaultConnectionFactory type="System.Data.Entity.Infrastructure.SqlConnectionFactory, EntityFramework" />
<provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />

and adding the connnection strings section, the following error  occurs…

Top-level Exception
Type: System.InvalidOperationException
Message: The Entity Framework provider type 'System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer' registered in the application config file for the ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded. Make sure that the assembly-qualified name is used and that the assembly is available to the running application. See for more information.
Source: EntityFramework
Stack Trace: at System.Data.Entity.Infrastructure.DependencyResolution.ProviderServicesFactory.GetInstance(String providerTypeName, String providerInvariantName)
at System.Data.Entity.Internal.AppConfig.<;.ctor>b__2(ProviderElement e)
at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
at System.Data.Entity.Internal.AppConfig.<;.ctor>b__1()
at System.Lazy`1.CreateValue()
at System.Lazy`1.LazyInitValue()
at System.Lazy`1.get_Value()
at System.Data.Entity.Internal.AppConfig.get_DbProviderServices()
at System.Data.Entity.Infrastructure.DependencyResolution.AppConfigDependencyResolver.RegisterDbProviderServices()
at System.Data.Entity.Infrastructure.DependencyResolution.AppConfigDependencyResolver.GetServiceFactory(Type type, String name)
at System.Data.Entity.Infrastructure.DependencyResolution.AppConfigDependencyResolver.<;>c__DisplayClass1.<GetService>b__0(Tuple`2 t)
at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
at System.Data.Entity.Infrastructure.DependencyResolution.AppConfigDependencyResolver.GetService(Type type, Object key)
at System.Data.Entity.Infrastructure.DependencyResolution.ResolverChain.<;>c__DisplayClass3.<GetService>b__0(IDbDependencyResolver r)
at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source, Func`2 predicate)
at System.Data.Entity.Infrastructure.DependencyResolution.ResolverChain.GetService(Type type, Object key)
at System.Data.Entity.Infrastructure.DependencyResolution.CompositeResolver`2.GetService(Type type, Object key)
at System.Data.Entity.Infrastructure.DependencyResolution.DbDependencyResolverExtensions.GetService[T](IDbDependencyResolver resolver, Object key)
at System.Data.Entity.Core.EntityClient.EntityConnection.ChangeConnectionString(String newConnectionString)
at System.Data.Entity.Core.EntityClient.EntityConnection..ctor(String connectionString)
at canford.SalesOrderProcessingEntities.GetSqlConnection(String ConnectionString)

Seems that as I have all the data access defined in its own class lib, there is no code causing a reference to force the correct EntityFramework.SqlServer.dll to be pushed to the build output.

So this hack did the job for now and I’ve posted this here to come back to another time.

Stack overflow post: EntityFramework.SqlServer.dll not is getting added

private void FixEfProviderServicesProblem()
// The Entity Framework provider type 'System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer'
// for the 'System.Data.SqlClient' ADO.NET provider could not be loaded.
// Make sure the provider assembly is available to the running application.
// See for more information.
var instance = System.Data.Entity.SqlServer.SqlProviderServices.Instance;

UWP Serial Port Missing Bytes, Bytes Written Windows IoT

Whilst writing a PCX format, 1 bit per pixel (1bpp) byte array to a serial port FTDI USB serial adapter using WinRT/UWP, on a Laptop (using for developing before deploying to RPi2), it kept failing to work correctly. The serial port was going to the RS232 input of a Zebra Thermal printer, the PCX representing a bitmap to print. The code below was used to push the byte array through to the serial port, after failing to find any answers on line and eliminating other possibilities, a logic analyser on the serial port uncovered the issue. The bye array was not complete.  

public async Task Print(byte[] bytesTosend)
using (DataWriter dataWriteObject = new DataWriter(serialPort.OutputStream))
await WriteBytesAsync(dataWriteObject, bytesTosend);
if (dataWriteObject != null)

public async Task WriteBytesAsync(DataWriter dataWriteObject, byte[] bytesTosend)
Task<UInt32> storeAsyncTask;
int offset = 0;
int buffersize = bytesTosend.Length;
//if (buffersize > 1000) { buffersize = 1000; }
byte[] sendBuffer = new byte[buffersize];
System.Buffer.BlockCopy(bytesTosend, offset, sendBuffer, 0, buffersize);
storeAsyncTask = dataWriteObject.StoreAsync().AsTask();
UInt32 bytesWritten = await storeAsyncTask;
offset += buffersize;
} while (offset < bytesTosend.Length);

Running the code in debug and looking at the length of the byte array, compared to the bytes sent, the problem is clear to see. The image is 200x200 pixels, so at 1bpp this is 200/8 bytes wide * 200 rows = 5000 bytes.

Indeed the byte array is 5000 bytes to send, but wait look at how many bytes have actually been sent, 4096 bytes! Somewhere four bytes have gone missing, thus the printer is awaiting the complete image and does not print.

 Byte writing code showing the debug values

There seems to be no way to flush the buffer or any other methods on the DataWriter that could be used to force these extra bytes out, anyway the missing bytes might not necessarily from the end of the array. There is a FlushAsync method, however that returns a “not implemented” exception – gotta love coding on this platform…

So perhaps by gut says this is actually some kind of serial buffer overflow problem. Some support to this theory is that writing low numbers of bytes to the serial port works just fine.


Fixing serial port write on UWP application missing bytes

MakerFaire is in three weeks time so a solution is needed quick, not time to raise with Microsoft. As smaller writes works, and my suspicion is a buffer overflow, the solution is to uncomment the commented out line in the code above. This will break any byte array larger than one thousand bytes into chunks and send them one chunk at a time.

Running the code worked, printing the image perfectly every time.

This seems to be how it is in the world of Windows IoT and UWP at the moment, if feels like the first couple of years of the first versions of .NET all over again!

Visual Studio 2015 Licence Error (0x00000002): Unable to save downloaded online licence

I just experienced this error in Visual studio with a sole button to “close visual studio”.


It happened on opening projects. I ended up having to log out of my MSDN account on that same error window and back in again before it would allow me forward.

Clicking the “Check for an updated license” only worked after that logout and in process.

Seems others have seen this too Visual Studio 2015 fails to check license (unable to save downloaded online license)

I wonder if it is a transient connectivity issue with license webservices or a deeper issue of some kind.