XRS10L220 Datasheet, PDF (10/38 Pages) Exar Corporation – SERIAL ATA II: PORT MULTIPLIER / PORT SELECTOR

EXSTOR - 1 XRS10L220
SERIAL ATA II: PORT MULTIPLIER / PORT SELECTOR
REV. 1.02
The two host ports are responsible for coordination of access to the XRS10L220 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 XRS10L220. 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 XRS10L220 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 intial 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 XRS10L220 also features support for a sideband port selection mechanism. This is implemented via the
MDIO register settings. 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 XRS10L220 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.
A Serial ATA II Port Multiplier is a mechanism for one active host connection to communicate with multiple
devices. A Port Multiplier is conceptually a simple multiplexer in which one active host connection is
multiplexed to multiple device connections.
The XRS10L220 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 1 are valid device ports within the 2-
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