StagingBuff: Enhance IoConstraints with frame constraints

Now StagingBuff instances must meed both frame and slot
constraints.

stimBuffApis/livoxGen1/stagingBuffer.h

@@ -36,15 +36,19 @@ public:
 	public:
 		IOEngineConstraints(
 			size_t slotStartAlignmentByteVal_,
-			size_t slotPadToNBytes_)
+			size_t slotPadToNBytes_,
+			size_t frameStartAlignmentByteVal_,
+			size_t framePadToNBytes_)
 		: slotStartAlignmentByteVal(slotStartAlignmentByteVal_),
-		  slotPadToNBytes(slotPadToNBytes_)
+		slotPadToNBytes(slotPadToNBytes_),
+		frameStartAlignmentByteVal(frameStartAlignmentByteVal_),
+		framePadToNBytes(framePadToNBytes_)
 		{}
 
 		~IOEngineConstraints() = default;
 
-		size_t slotStartAlignmentByteVal;  // power-of-2 alignment (e.g., 4096)
-		size_t slotPadToNBytes;            // minimum size per datagram slot
+		size_t slotStartAlignmentByteVal, slotPadToNBytes,
+			frameStartAlignmentByteVal, framePadToNBytes;
 
 		// Static defaults for io_uring and OpenCL
 		static const IOEngineConstraints ioUringConstraints;
@@ -56,6 +60,8 @@ public:
 			oss << "IOEngineConstraints{"
 				<< "slotStartAlignmentByteVal=" << slotStartAlignmentByteVal
 				<< ", slotPadToNBytes=" << slotPadToNBytes
+				<< ", frameStartAlignmentByteVal=" << frameStartAlignmentByteVal
+				<< ", framePadToNBytes=" << framePadToNBytes
 				<< "}";
 			return oss.str();
 		}
@@ -118,6 +124,12 @@ public:
 
 private:
 	void computeSlotStrideAndBufferSize();
+	static size_t calculateFirstSlotOffsetAndValidate(
+		uint8_t* buffer,
+		size_t bufferNBytes,
+		size_t nDgramsPerFrame,
+		size_t slotStrideNBytes,
+		const IOEngineConstraints& inputConstraints);
 
 	// Custom deleter for mmap-allocated buffer
 	struct MmapDeleter
@@ -143,6 +155,7 @@ private:
 	// Layout/invariants
 	size_t nDgramsPerFrame;
 	size_t slotStrideNBytes;
+	size_t firstSlotOffsetNBytes;  // offset from buffer start to first slot
 	IOEngineConstraints inputConstraints;
 
 	// Descriptor (computed once; reused across frames)
@@ -162,6 +175,7 @@ inline StagingBuffer::StagingBuffer(
 	size_t nDgramsPerFrame)
 : buffer(nullptr, MmapDeleter(0)), bufferNBytes(0),
 nDgramsPerFrame(nDgramsPerFrame), slotStrideNBytes(0),
+firstSlotOffsetNBytes(0),
 inputConstraints(inputEngineConstraints_),
 assemblingFlag(false)
 {
@@ -192,10 +206,15 @@ assemblingFlag(false)
 		static_cast<uint8_t*>(mmapped), MmapDeleter(bufferNBytes));
 	currentNBytes.store(0);
 
+	// Calculate offset and validate invariants (helper function in .cpp)
+	firstSlotOffsetNBytes = StagingBuffer::calculateFirstSlotOffsetAndValidate(
+		buffer.get(), bufferNBytes, nDgramsPerFrame,
+		slotStrideNBytes, inputConstraints);
+
 	// Build FrameAssemblyDesc once
 	std::vector<FrameAssemblyDesc::SlotDesc> slots;
 	slots.reserve(nDgramsPerFrame);
-	uint8_t *frameBase = buffer.get();
+	uint8_t *frameBase = buffer.get() + firstSlotOffsetNBytes;
 	for (size_t i = 0; i < nDgramsPerFrame; ++i)
 	{
 		size_t off = i * slotStrideNBytes;
@@ -210,20 +229,6 @@ assemblingFlag(false)
 		std::move(slots));
 }
 
-inline void StagingBuffer::computeSlotStrideAndBufferSize()
-{
-	// Slot stride is the maximum of alignment and padding
-	slotStrideNBytes = std::max(
-		inputConstraints.slotStartAlignmentByteVal,
-		inputConstraints.slotPadToNBytes);
-
-	// Buffer size is nDgramsPerFrame * slotStrideNBytes, aligned up to alignment
-	size_t rawSize = nDgramsPerFrame * slotStrideNBytes;
-	bufferNBytes = ((rawSize + inputConstraints.slotStartAlignmentByteVal - 1)
-	                / inputConstraints.slotStartAlignmentByteVal)
-	               * inputConstraints.slotStartAlignmentByteVal;
-}
-
 } // namespace stim_buff
 } // namespace smo