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Check padding and bandwidth
Distinguish operand validity from result-address validity.
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The final spatial tile of a 3×3 result on an N=2 grid has one real output. The simple completion contract requires every PE to consume K terms, including padded rows and columns.
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What goes wrong if padding is invalid but completion waits for every count to equal K?
Read the explanation
Padded PEs never consume enough terms, so their counts never reach K. Supply valid zero tokens and independently mask result stores by coordinates.
Which boundary-padding policy is correct?
Valid zero preserves the K-term completion contract. The output mask prevents out-of-range stores; numerical value and address validity are independent.
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