Aligning Serial ATA Bit Steams at the Physical Layer
When transmitting Serial ATA data over the physical layer, it is necessary that the transmitter and receiver are aligned so that the data is properly interpreted. The Serial ATA specification, as well as physical layer receiver implementations offer many tools to accurately realign the incoming bit stream. Among those tools are the ALIGN primitive, used as a separator or "comma", inserted directly into the bit stream; and the concepts of tracking and oversampling on the receiving end. This article explores these tools and the details behind what makes them effective, as well as managing frequency mismatches that will inevitably occur between transmitters and receivers, and spread spectrum clocking.
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