XRS10L240 Datasheet, PDF (12/38 Pages) Exar Corporation – SERIAL ATA II: PORT MULTIPLIER / PORT SELECTOR

EXSTOR - 1 XRS10L240
SERIAL ATA II: PORT MULTIPLIER / PORT SELECTOR
REV. 1.05
The XRS10L240 provides full support for the Serial ATA II Port Selector specification. A Serial ATA Port
Selector is a mechanism that allows two different host ports to connect to the same device in order to create a
redundant path to that device. Only one host connection to the device is active at a time.
The two host ports are responsible for coordination of access to the XRS10L240 by one of two separate
means: protocol-based port selection or sideband port selection. Each method is described in detail in the next
two sections.
3.4.1 Protocol Based Port Selection
Protocol-based port selection makes use of a sequence of Serial ATA OOB signals to select the active host
port. The port selection signal is based on a pattern of COMRESET OOB signals transmitted from the host to
the XRS10L240. The port selection signal is composed of a series of COMRESET signals with the timing from
one COMRESET signal to the next as shown in Table 3 and Figure 8. The XRS10L240 selects the port, if
inactive, on the de-assertion of COMRESET after receiving two complete back-to-back sequences with this
defined inter-burst spacing. This can also be identified as two sequences of two COMRESET intervals
comprising a total of five COMRESET bursts with four inter-burst delays. Once a port is designated as active,
reception of additional COMRESET signals is propagated directly to the device, even if the COMRESET
signals constitute a port selection signal.
Note that when protocol based selection mode has been enabled, following the initial hardware reset, a single
COMRESET burst will select the active host port. After this initial host port selection, only COMRESET OOB
observing the protocol timing given below will change the active host.
TABLE 3: PORT SELECTOR SIGNAL INTER-RESET TIMING REQUIREMENTS
NOMINAL
MIN.
MAX
UNITS
COMMENTS
T1
2.0
1.6
2.4
ms
Inter-reset assertion delay for first
event of the selection sequence
T2
8.0
7.6
8.4
ms
Inter-reset assertion delay for second
event of the selection sequence
FIGURE 8. PORT SELECTION SIGNAL - TRANSMITTED COMRESET SIGNALS
3.4.2 Sideband Based Port Selection
The XRS10L240 also features support for a sideband port selection mechanism. This is implemented using a
combination of the MDIO register settings and device pins including PS_SIDEBAND_B and PORTSEL. Refer
to Table 2 for a sideband port selection settings.
3.5 Port Multiplier Implementation
The XRS10L240 provides full support for the functionality outlined in the Serial ATA II Port Multiplier
specification. This Port Multiplier functionality follows the Port Selector implementation, and only one link can
be active at any time.
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