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XRS10L140 Datasheet(PDF) 10 Page - Exar Corporation |
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XRS10L140 Datasheet(HTML) 10 Page - Exar Corporation |
10 / 36 page EXSTOR XRS10L140 10 SERIAL ATA II: PORT MULTIPLIER REV. 1.05 with multiple devices. A Port Multiplier is conceptually a simple multiplexer in which one active host connection is multiplexed to multiple device connections. The XRS10L140 uses four bits, known as the PM Port field in all Serial ATA frame types, to route frames between the selected host and the appropriate device. PM ports 0 through 3 are valid device ports within the 4- output XRS10L140, while PM port 15 is designated for communication between the host and the XRS10L140 itself. For host-to-device transactions, the PM Port field is designated by the host in order to specify which device the frame is intended for. For device-to-host transactions, the XRS10L140 fills in the PM Port field with the port address of the device that is transmitting the frame. The PM Port field is defined in the Serial ATA port multiplier specification to be the first 32-bit Dword in the Frame Information Structure (FIS) for all FIS types, as shown in Figure 8. 3.4.1 Transmission from a host to a device A host indicates the target device for receipt of a transmitted frame by setting the PM Port field in the frame to the device's port address. When an XRS10L140 receives a frame from the host, it checks the PM Port field in the frame to determine which port address should be used. If the frame is set for transmission to the control port (15), the XRS10L140 receives the frame and performs the command or operation requested. If the frame is designated for a device port, the XRS10L140 obeys the following procedure: 1. The XRS10L140 first determines if the device port is valid. If the device port is not valid, the XRS10L140 will issue a SYNC primitive to the host and terminate reception of the frame. 2. The XRS10L140 determines if the X bit is set in the device port's PSCR[1] (SError) register. If the X bit is set, the XRS10L140 issues a SYNC primitive to the host and terminates reception of the frame. 3. The XRS10L140 determines if a collision has occurred. A collision occurs when a reception is already in progress from the device that the host wants to transmit to. If a collision has occurred, the XRS10L140 will finish receiving the frame from the host and will then issue an R_ERR primitive to the host as the ending status. The XRS10L140 will then discard the frame, but will not return an R_RDY primitive to the host until the frame from the affected device port has been transmitted to the host, thus indicating to the host when it can retry to send the frame. The transmission from the device will proceed as requested, as the device will always take collision precedence over the host. 4. The XRS10L140 initiates a transfer with the device by issuing an X_RDY primitive to the device. A collision may occur as the XRS10L140 is issuing the X_RDY to the device if the device has started transmitting an X_RDY primitive to the XRS10L140, indicating a decision to start a transmission to the host. In this case, the XRS10L140 will finish receiving the frame from the host and then issue an R_ERR primitive to the host to indicate an unsuccessful transmission. The transmission from the device will proceed as requested, as the device will always take collision precedence over the host. 5. After the device issues an R_RDY primitive to the XRS10L140, the XRS10L140 will transmit the frame from the host to the device. The XRS10L140 will not send an R_OK status primitive to the host until the device has issued an R_OK primitive to indicate successful frame reception. In this way, the R_OK status handshake is interlocked from the device to the host. If an error is detected during any part of the frame transfer, the XRS10L140 will ensure that the error condition is propagated to the host and the device. If no error occurs during frame transfer, the XRS10L140 will not alter the contents of the frame, or modify the CRC in any way. 3.4.2 Transmission from a device to a host A device indicates a transmit to a host in the same way as would be done if the host and device were attached directly. This transaction obeys the following procedure: FIGURE 8. PORT SELECTION SIGNAL - TRANSMITTED COMRESET SIGNALS FIS Type PM Port As defined in Serial ATA1.0 |
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Similar Description - XRS10L140 |
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