Unmanaged Heap

The unmanaged heap is a region of memory that lives outside the garbage-collected managed heap — typically backed by external SDRAM on devices that have it. Most SITCore SoMs include 32 MB of external SDRAM for this purpose.

Use it when you need:

• Large buffers (audio samples, sensor capture, file caches) that don't fit comfortably in internal RAM.
• Graphics framebuffers — the graphics engine automatically allocates from unmanaged heap when external SDRAM is available.

The trade-off vs the managed heap:

• ✅ Much more space than internal RAM allows
• ✅ No GC pressure or compaction cost
• ⚠️ Not secure — external SDRAM can be probed (see External Memory)
• ⚠️ Manual lifetime — you have to Dispose() buffers yourself

NuGet package: GHIElectronics.TinyCLR.Native.

UnmanagedBuffer

UnmanagedBuffer is the convenient way to allocate a chunk of unmanaged heap, expose it as a normal byte[], and release it when done. The example below allocates a 100 KB buffer on an SCM20260D Dev Board:

using GHIElectronics.TinyCLR.Native;

// Allocate 100,000 bytes in unmanaged heap.
var uBuffer = new UnmanagedBuffer(100000);
var uTable = uBuffer.Bytes;     // Usable as a regular byte[].

// ... use uTable ...

// Release the unmanaged memory — mandatory, the GC won't do it for you.
uBuffer.Dispose();

warning

You must call Dispose() on UnmanagedBuffer — there's no automatic cleanup. Wrap the buffer in a using block if its lifetime fits a single scope.

tip

For sensitive data, encrypt the contents before putting them in the unmanaged buffer. See Cryptography for the available algorithms.

Graphics memory

When external SDRAM is present, the graphics engine automatically allocates its display buffers, bitmaps, and intermediate render targets from the unmanaged heap — no special API needed. Graphics buffers are exempt from the manual-disposal rule: garbage collection handles graphics buffers in unmanaged heap automatically.

This means a typical graphics-heavy application doesn't see the unmanaged heap directly. It only matters when you're explicitly allocating large buffers via UnmanagedBuffer.

Checking unmanaged heap usage

Same pattern as managed memory — useful for debugging leaks and tuning buffer sizes:

using GHIElectronics.TinyCLR.Native;
using System.Diagnostics;

Debug.WriteLine("Unmanaged free:  " + Memory.UnmanagedMemory.FreeBytes);
Debug.WriteLine("Unmanaged used:  " + Memory.UnmanagedMemory.UsedBytes);

API reference

Namespace	Description
GHIElectronics.TinyCLR.Native	Unmanaged heap allocation and pointer access