diff --git a/BizHawk.Emulation.Common/Base Implementations/BasicServiceProvider.cs b/BizHawk.Emulation.Common/Base Implementations/BasicServiceProvider.cs
index 30c7c9d5b8..b0d653cd7c 100644
--- a/BizHawk.Emulation.Common/Base Implementations/BasicServiceProvider.cs	
+++ b/BizHawk.Emulation.Common/Base Implementations/BasicServiceProvider.cs	
@@ -45,6 +45,17 @@ namespace BizHawk.Emulation.Common
 			}
 		}
 
+		/// <summary>
+		/// the core can call this to register an additional service
+		/// </summary>
+		/// <typeparam name="T"></typeparam>
+		/// <param name="provider"></param>
+		public void Register<T>(T provider)
+			where T : IEmulatorService
+		{
+			Services[typeof(T)] = provider;
+		}
+
 		public IEmulatorService GetService<T>()
 			where T : IEmulatorService
 		{
diff --git a/BizHawk.Emulation.Common/Interfaces/IDisassemblable.cs b/BizHawk.Emulation.Common/Interfaces/IDisassemblable.cs
index 29067ad9ab..d3611faacd 100644
--- a/BizHawk.Emulation.Common/Interfaces/IDisassemblable.cs
+++ b/BizHawk.Emulation.Common/Interfaces/IDisassemblable.cs
@@ -1,8 +1,10 @@
-using System.Collections.Generic;
+using System;
+using System.Linq;
+using System.Collections.Generic;
 
 namespace BizHawk.Emulation.Common
 {
-	public interface IDisassemblable : IEmulator, IEmulatorService
+	public interface IDisassemblable : IEmulatorService
 	{
 		/// <summary>
 		/// Gets or sets the Cpu that will be used to disassemble
@@ -13,11 +15,45 @@ namespace BizHawk.Emulation.Common
 		/// <summary>
 		/// Gets a list of Cpus that can be used when setting the Cpu property
 		/// </summary>
-		IEnumerable<string> AvailableCpus { get; set; }
+		IEnumerable<string> AvailableCpus { get; }
 
 		/// <summary>
 		/// returns a disassembly starting at addr lasting for length, using the given domain
 		/// </summary>
 		string Disassemble(MemoryDomain m, uint addr, out int length);
 	}
+
+	/// <summary>
+	/// does santiy checking on Cpu parameters
+	/// </summary>
+	public abstract class VerifiedDisassembler : IDisassemblable
+	{
+		protected string _cpu;
+
+		public virtual string Cpu
+		{
+			get
+			{
+				return _cpu;
+			}
+			set
+			{
+				if (!AvailableCpus.Contains(value))
+					throw new ArgumentException();
+				_cpu = value;
+			}
+		}
+
+		public abstract IEnumerable<string> AvailableCpus
+		{
+			get;
+		}
+
+		public abstract string Disassemble(MemoryDomain m, uint addr, out int length);
+
+		public VerifiedDisassembler()
+		{
+			_cpu = AvailableCpus.First();
+		}
+	}
 }
diff --git a/BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj b/BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj
index e2f41d8526..c76ea7263c 100644
--- a/BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj
+++ b/BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj
@@ -274,6 +274,7 @@
     <Compile Include="Consoles\Nintendo\Gameboy\GambatteLink.cs" />
     <Compile Include="Consoles\Nintendo\Gameboy\GBColors.cs" />
     <Compile Include="Consoles\Nintendo\Gameboy\LibGambatte.cs" />
+    <Compile Include="Consoles\Nintendo\GBA\ArmV4Disassembler.cs" />
     <Compile Include="Consoles\Nintendo\GBA\IGBAGPUViewable.cs" />
     <Compile Include="Consoles\Nintendo\GBA\LibMeteor.cs" />
     <Compile Include="Consoles\Nintendo\GBA\LibVBANext.cs" />
diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/GBA/ArmV4Disassembler.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/GBA/ArmV4Disassembler.cs
new file mode 100644
index 0000000000..af09c8ab90
--- /dev/null
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/GBA/ArmV4Disassembler.cs
@@ -0,0 +1,42 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using BizHawk.Emulation.Common;
+
+namespace BizHawk.Emulation.Cores.Nintendo.GBA
+{
+	public class ArmV4Disassembler : VerifiedDisassembler
+	{
+		public override IEnumerable<string> AvailableCpus
+		{
+			get
+			{
+				return new[] { "ARM v4", "ARM v4 (Thumb)" };
+			}
+		}
+
+		public override string Disassemble(MemoryDomain m, uint addr, out int length)
+		{
+			if (_cpu == "ARM v4 (Thumb)")
+			{
+				addr &= unchecked((uint)~1);
+				int op = m.PeekByte((int)addr) | m.PeekByte((int)addr + 1) << 8;
+				string ret = Emulation.Cores.Components.ARM.Darm.DisassembleStuff(addr | 1, (uint)op);
+				length = 2;
+				return ret;
+			}
+			else
+			{
+				addr &= unchecked((uint)~3);
+				int op = m.PeekByte((int)addr)
+					| m.PeekByte((int)addr + 1) << 8
+					| m.PeekByte((int)addr + 2) << 16
+					| m.PeekByte((int)addr + 3) << 24;
+				string ret = Emulation.Cores.Components.ARM.Darm.DisassembleStuff(addr, (uint)op);
+				length = 4;
+				return ret;
+			}
+		}
+	}
+}
diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/GBA/VBANext.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/GBA/VBANext.cs
index f1d1125183..3edc338189 100644
--- a/BizHawk.Emulation.Cores/Consoles/Nintendo/GBA/VBANext.cs
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/GBA/VBANext.cs
@@ -23,7 +23,10 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBA
 		[CoreConstructor("GBA")]
 		public VBANext(byte[] file, CoreComm comm, GameInfo game, bool deterministic, object syncsettings)
 		{
-			ServiceProvider = new BasicServiceProvider(this);
+			var ser = new BasicServiceProvider(this);
+			ser.Register<IDisassemblable>(new ArmV4Disassembler());
+			ServiceProvider = ser;
+
 			CoreComm = comm;
 
 			byte[] biosfile = CoreComm.CoreFileProvider.GetFirmware("GBA", "Bios", true, "GBA bios file is mandatory.");