GPU frame mapping illegal memory access: check pitch and planes

A camera stream can run normally for minutes before an image-processing operation reports illegal device-memory access. The failure may appear during conversion, copying or cleanup, even though an earlier operation caused it. For developers wrapping captured surfaces as image matrices, the first task is to prove that the memory is accessible, correctly described and still owned. The workflow below separates those checks so you can identify the failing boundary without replacing working acquisition hardware.

Start with the first failing operation

Treat GPU frame mapping illegal memory access as a memory-contract problem before treating it as a performance problem. A valid image view needs an accessible allocation, the correct surface and plane, accurate layout metadata, and ownership lasting through the final read.

Use this order as a diagnostic priority, not a claim about which fault is most common:

Record the earliest failed operation, frame identifier and allocation generation. Later errors during clearing or freeing memory may be consequences rather than separate causes.

Device operations can execute asynchronously. During a controlled diagnostic run, add documented completion checks after import, conversion and processing. This narrows the failure to a stage, although the additional waiting changes throughput and timing.

For native host crashes rather than device-access errors, use the separate workflow for camera integration access violations.

Prove that the pointer is accessible

A pointer-shaped value does not establish that ordinary CPU code can read the underlying pixels. It might identify device memory, mapped host memory, an opaque surface, or a descriptor containing other addresses.

Before creating an image view, obtain these facts from the acquisition API:

• Allocation type and owning subsystem.
• Whether CPU access requires an explicit map operation.
• Whether device access requires an import or registration operation.
• Whether the returned layout is linear or uses another representation.
• Required cache-coherency operations and mapping lifetime.

A CPU image matrix must not wrap device-only storage and then pass it to an ordinary host copy. Likewise, a device image view needs an address accessible to the selected device context. A cast changes the pointer type, not its accessibility.

First test the documented copy into independently owned host memory. If that works while direct wrapping fails, investigate mapping, layout and lifetime before blaming the camera link. This is an isolation test, not proof that every conversion setting is correct.

For a linear device view, confirm that the mapping API actually exposes linear storage. A surface using tiled or opaque storage cannot be interpreted merely by guessing a pitch.

Separate batch entries from image planes

A batch index selects a captured surface within a batch. A plane index selects a component of that surface's memory layout. These are different dimensions of the descriptor.

A packed colour image may have one plane containing several components per pixel. A planar or semiplanar format can expose multiple planes with different dimensions, pitches and element interpretations. Do not infer plane count from the number of colour components.

For each acquired surface, record:

• Valid batch entries and the selected entry.
• Format identifier, width and height.
• Valid plane count.
• Per-plane pointer or mapped handle, offset, pitch and accessible extent.
• The documented meaning of each plane's width and height.

Use the API's metadata definitions when interpreting those fields. A width might describe pixels, samples or another documented unit; it is not automatically a byte count.

Map the selected batch entry and plane through the supported interface. Do not substitute a surface descriptor address for a pixel pointer. Do not add a plane offset twice when the returned pointer already addresses the plane.

Re-read descriptors after a format change, resolution change or stream restart. Old metadata can remain plausible while referring to an allocation that no longer exists.

Check row pitch with explicit arithmetic

Row pitch is the byte distance between corresponding positions in adjacent rows. It can exceed the number of useful bytes in a row because of alignment or allocation requirements.

For a simple, linear, unpacked plane, validate the following quantities:

These equations assume positive pitch, a nonempty plane and no extra packing rules. Use the documented layout calculation for packed formats or other representations.

Consider a hypothetical image with 1920 pixels per row, 1080 rows and four bytes per pixel. Its mapped pitch is 8192 bytes:

The mapping's accessible extent, measured from the plane start, must cover the minimum span. Do not assume the complete pitched extent is accessible merely because the arithmetic suggests it.

Using a tight stride would place row 100 at byte 768000. The correct pitched offset is 819200, a difference of 51200 bytes. That mistake can produce corrupted rows without immediately leaving the allocation. Other stride or extent mistakes can cause an illegal access.

A cropped view normally retains its parent image's pitch. Reducing its width does not remove padding or change the spacing between parent rows. Calculate the crop offset separately and validate the remaining accessible span.

For a related treatment of array layout, GPU point cloud shapes, strides and alignment explains why matching dimensions alone is insufficient.

Match pixel format to the processing view

Correct addresses still produce incorrect access when the processing view describes the wrong element type. Record storage depth, component count, packing, channel order and plane organization separately.

For example, a hypothetical packed three-component image uses three bytes per pixel when each component occupies one byte. Describing it as a four-component image changes the expected row length and every horizontal pixel offset.

Similarly, a sensor's meaningful bit depth does not necessarily equal its storage size. Samples may occupy wider containers or use packed groups. Determine the actual transport and mapped format instead of calculating storage from meaningful bits alone.

Check these boundaries independently:

1. The camera's transmitted format.
2. The acquisition subsystem's delivered format.
3. The mapped surface format.
4. The format expected by the processing operation.

An acquisition subsystem may perform conversion, so the camera setting alone is not sufficient evidence. Compare the descriptor immediately before constructing the processing view.

For subsampled colour, process each plane according to its documented geometry or use a supported conversion. Do not expose a luma plane as a full-resolution colour image.

Use a stationary target with distinct bright, dark and coloured regions. Compare a trusted copied image with the mapped processing result. Look for displaced rows, swapped components, repeated regions and errors at image edges.

Retain the capture buffer through device completion

Creating an image header usually creates a view, not an independent pixel allocation. Returning the capture buffer can therefore invalidate work that still references it.

Consider a hypothetical callback that submits device work and returns the buffer after 2 ms. If the final device read finishes after 12 ms, the allocation has a 10 ms interval during which acquisition may reuse it. Fast average processing does not close that ownership gap.

The required dependency chain is:

Cross-stream execution requires the appropriate event or fence dependency. Waiting on the wrong stream does not prove that the actual consumer has finished.

If retaining acquisition buffers is unsupported or harms capture continuity, copy into an owned processing pool. The source must remain valid until the copy completes. The destination must remain valid until every downstream operation completes.

CPU mapping can also require explicit coherency operations before reads or after writes. Follow the documented sequence; mapping and waiting for device work are not interchangeable operations.

The ownership principles in camera frame memory lifetime apply here too. The additional requirement is that asynchronous device completion, rather than callback return, determines the final-use boundary.

Isolate the failing boundary with controlled tests

Change one boundary at a time and keep a known-good baseline. Otherwise, a format correction can hide an unrelated synchronization defect.

1. Run acquisition without downstream processing. Record delivered frames, acquisition errors and buffer returns.
2. Use the documented copy into owned memory. Verify image content and dimensions before adding device processing.
3. Validate a single mapped frame. Check every descriptor field, run one operation, wait for completion, then release it.
4. Enable continuous processing with explicit completion waits. Keep ownership rules identical across all frames.
5. Restore asynchronous overlap gradually. Add explicit dependencies and bounded queues before increasing concurrency.

If copied processing works but mapped processing fails, concentrate on import, pitch, format and ownership. If both paths fail before processing starts, return to acquisition configuration and transport diagnostics.

Log frame identifiers alongside allocation identity and generation. Reused pointer values are normal in buffer pools; the same address does not mean the same frame remains valid.

After an illegal device access, stop the test and follow the runtime's documented recovery procedure. Do not assume later cleanup errors are independent or that the existing processing context remains usable.

Once correctness is established, use slow GPU image processing diagnostics to investigate throughput without confusing performance with memory validity.

Check hardware requirements before ordering replacements

An interface label does not establish direct device-memory import support. Confirm the acquisition driver, operating system, allocation types and supported processing interoperation together.

Use area scan cameras and the camera finder to identify acquisition options. The LS-CMR-0053 is a GigE area scan camera. Its catalog listing does not establish a device-mapping path.

For host connectivity, review frame grabbers and the accessory finder. The LS-FGB-0004 is a PoE Gigabit Ethernet card. Do not infer direct GPU access from that description.

When evaluating vision controllers, request confirmation of the complete acquisition and processing stack. Port count and installed memory alone do not establish compatibility with a particular surface-import mechanism.

Before choosing a lower-copy architecture, distinguish link transport, host buffering and device transfer. The guide to camera-to-GPU data transfer addresses that broader design decision.

Verify the fix under sustained acquisition

A successful single-frame test proves little about buffer reuse. Run the corrected pipeline under sustained acquisition, including the longest expected processing delays and normal stop-start transitions.

If the previous failure appeared after roughly 20 minutes, a 60-minute run provides a useful initial comparison, not a reliability guarantee. Also test queue saturation and repeated shutdown because ownership faults often depend on those conditions.

Use this acceptance checklist:

• Every view uses current surface and plane metadata.
• Every linear row access fits within the documented accessible extent.
• Processing types match the delivered storage format.
• Capture readiness and final-consumer completion have explicit dependencies.
• Buffer release occurs exactly once, after the final reader finishes.
• Queue capacity is bounded, with a defined backpressure or frame-drop policy.
• Shutdown stops new submissions and resolves outstanding work before releasing resources.
• Diagnostic logging preserves the first failure rather than only cleanup messages.

Do not accept a fix that merely adds enough buffers to postpone the crash. Additional buffering can support throughput, but it cannot replace a valid ownership contract.

If you need help separating hardware compatibility from a mapping defect, send the allocation type, plane descriptors, processing format and ownership timeline through application support. Those details make the next test more useful than replacing parts without evidence.