The PHY control layer operates between the PS-GTR and link layers. The main functions of the PHY control layer are listed.
•Data path operation.
•RX data path.
•TX data path.
•PHY initialization state machine.
On receive, the PHY control layer converts the encoded 20-bit parallel data from the PS-GTR to a 32-bit double word, which it presents to the link layer. The PHY control layer aligns the control word of the SATA primitive to the lowest word position of the double word. The PHY control contains an 8B/10B decoder function and decodes the incoming data into data, control/data and code, or disparity error. The PHY controller sends data, control/data and code, or disparity error to the PS-GTR.
On transmit, the PHY control layer takes in the 32-bit transmit data from the link layer and converts the data into encoded 20-bit parallel data to the PS-GTR. The control/data bit from the link layer (which is always assumed to be associated with the lowest byte position of the transmit double word) is also passed onto the PS-GTR with the appropriate word. The PHY control layer takes the transmit word clock output by the PS-GTR and converts it to a double word transmit clock which it sends to the link layer.