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XRS10L220IV Datasheet(PDF) 10 Page - Exar Corporation |
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XRS10L220IV Datasheet(HTML) 10 Page - Exar Corporation |
10 / 38 page EXSTOR - 1 XRS10L220 10 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. 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- 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 |
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