XRS10L220 Datasheet, PDF (11/38 Pages) Exar Corporation – SERIAL ATA II: PORT MULTIPLIER / PORT SELECTOR

EXSTOR - 1 XRS10L220
REV. 1.02
SERIAL ATA II: PORT MULTIPLIER / PORT SELECTOR
output XRS10L220, while PM port 15 is designated for communication between the host and the XRS10L220
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 XRS10L220 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 9.
FIGURE 9. PORT SELECTION SIGNAL - TRANSMITTED COMRESET SIGNALS
As defined in Serial ATA1.0
PM Port
FIS Type
3.5.1 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 XRS10L220 receives a frame as selected from one of the two available
hosts by the port selector, 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 XRS10L220 receives the frame and
performs the command or operation requested. If the frame is designated for a device port, the XRS10L220
obeys the following procedure:
1. The XRS10L220 first determines if the device port is valid. If the device port is not valid, the XRS10L220
will issue a SYNC primitive to the host and terminate reception of the frame.
2. The XRS10L220 determines if the X bit is set in the device port's PSCR[1] (SError) register. If the X bit is
set, the XRS10L220 issues a SYNC primitive to the host and terminates reception of the frame.
3. The XRS10L220 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 XRS10L220 will
finish receiving the frame from the host and will then issue an R_ERR primitive to the host as the ending
status. The XRS10L220 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 XRS10L220 initiates a transfer with the device by issuing an X_RDY primitive to the device. A collision
may occur as the XRS10L220 is issuing the X_RDY to the device if the device has started transmitting an
X_RDY primitive to the XRS10L220, indicating a decision to start a transmission to the host. In this case,
the XRS10L220 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 XRS10L220, the XRS10L220 will transmit the frame
from the host to the device. The XRS10L220 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 XRS10L220 will ensure that the error condition
is propagated to the host and the device. If no error occurs during frame transfer, the XRS10L220 will not alter
the contents of the frame, or modify the CRC in any way.
3.5.2 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:
1. After receiving an X_RDY primitive from the device, the XRS10L220 will determine if the X bit is set in the
device port's PSCR[1] (SError) register. The XRS10L220 will not issue an R_RDY primitive to the device
until this bit is cleared to zero.
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