08-052r7 Proposal for SAS 2.x Specification to Enable Support for Active Cables Gourgen Oganessyan QUELLAN August 12, 2008 Introduction
Inclusion of active cable interconnect option into the SAS specification would be beneficial in that it enables active copper and optical interconnects, to support longer reaches, lighter cable, etc. It is proposed that active cable support may be enabled in the intermediate SAS-2.x specification by making minimum changes to the SAS-2 spec and inserting a section on power supply option. A proposal for such changes and a stating point for the text of specification is presented. Change Log
Changes Since 01/08/2008
Removed the 1.2V power supply option ­ the proposal now has a single 3.3V supply. Added a section on capacitive coupling. Changes Since 02/12/2008
Added a sections, tables and figures for keying of active cable: prevents active cable from plugging into a passive port, while allowing passive cable to plug into an active port. Changes Since 03/07/2008
Fixed typos: Title of Table 60: Added the word "Mini" in front of "SAS" In Section 5.2.7.3.2 Power consumption replaced "per an interface" with "per cable"; the section now reads:" The voltage and current requirements are such as to enable support for active cable assemblies with power consumption at 3.3 V of up to 2 W per cable with four functioning links." In Section 5.2.7.3.2 Power consumption replaced "per an interface" with "per cable"; the section now reads:" The voltage and current requirements are such as to enable support for active cable assemblies with power consumption at 3.3 V of up to 2 W per cable with four functioning links." Changes Since 05/02/2008
Modified Section 5.2.7.3.6 Short Circuit Protection to read: "The active cable power supply shall have protection against the connection of the Vcc pin to ground, and shall limit short circuit current to below 25 mA when equivalent load resistance is less than 1 Ohm." Changes Since 05/15/2008
Collapsed the sections 5.2.7.3.2 - 5.2.7.3.2 into a single section 5.2.7.3.2 Power Supply Requirements, and summarized the numbers in a table (Table 61). Inserted the word "capacitors" in the last sentence of section 5.2.7.3.6 Bypassing. Modified Section 5.2.7.3.6 Short Circuit Protection to read: "The active cable power supply shall have protection against the connection of the Vcc pin to ground or over-current loading, and shall limit the output current when the equivalent load resistance is less than 1 Ohm". Added a change of wording to section 6.7.5 Phy reset sequence after devices are attached. Changes Since 06/05/2008
Added a proposed Informative Annex M for power supply logic reference design. Changes Since 07/11/2008
Edited most of the wording throughout the document to conform to the T10 style guide and to incorporate comments received from the group Deleted the minimum value for Supply Current in Table 61 and changed the maximum value from 600 mA to 319.4 mA. Edited the Informative Annex M to conform to the T10 style guide, dropped Table M.1 (parts List) and edited Figure M.1 to identify the function of the components. List of Proposed Modifications to SAS 2.0 to Enable Active Cables
· · · The title of section 5.2 "Passive Interconnect" shall be changed to read "Interconnect Characteristics". The title of subsection 5.2.4 "Cable assemblies" shall be changed to read "Passive Cable assemblies". The title of subsection 5.2.6 "Cable assembly and backplane specifications" shall be changed to read "Passive cable assembly and backplane specifications". A subsection 5.2.7 titled "Active Cables" shall be inserted with text as per pages 3-7 of this document. The table numbering in section 5.3 and onwards shall be changed so that Table 57 becomes Table 62, etc. The figure numbering in section 5.3 and onwards shall be changed so that Figure 98 becomes Figure 99, etc. Section 6.7.5 shall be reworded from the original text · · · · 6.7.5 Phy reset sequence after devices are attached Since SATA and SAS signal cable connectors do not include power lines, it is not possible to detect the physical insertion of the signal cable connector onto a plug. Non-cabled environments may similarly not have a way to detect physical insertion of a device. As a result, every time a phy reset sequence is originated: a) expander phys that are enabled but not active shall originate a new phy reset sequence repeatedly, with no more than a hot-plug timeout (see table 93 in 6.7.1) between each attempt, until a speed negotiation sequence completes successfully; b) SAS initiator phys should originate a new phy reset sequence after every hot-plug timeout; and c) SAS target phys should not originate a new phy reset sequence after their first attempt. to read:
6.7.5 Phy reset sequence after devices are attached Since it is not always possible to detect physical mating of a cable, every time a phy reset sequence is originated: a) expander phys that are enabled but not active shall originate a new phy reset sequence repeatedly, with no more than a hot-plug timeout (see table 94 in 6.7.1) between each attempt, until a speed negotiation sequence completes successfully; b) SAS initiator phys should originate a new phy reset sequence after every hot-plug timeout; and c) SAS target phys should not originate a new phy reset sequence after their first attempt 5.2.7 Active cables 5.2.7.1 Active cable overview
The standard provides support for the cable assemblies which incorporate active circuitry. This includes but is not limited to cables with built-in drivers, repeaters, equalizers, as well as copper cable substitutes which incorporate electro-optical converters and optical transceivers. In order to enable the operation of devices inside the active cable assemblies, 3.3 V power supply option is made available in the connectors. The powered ports receptacles defined in this standard are required to function when passive cables are plugged into them. This means that they must be able to handle the condition where their power supply pins are shorted to ground for any arbitrary length of time. Therefore, voltage sense pins are used to enable the switching of power in these ports. Active cable assemblies defined in this standard, when plugged into unpowered SAS 2.0 receptacles will not function. All active cables defined in this standard are external cable assemblies with active connectors defined in 5.2.7.2. The specification of high-speed data transmission performance of these cables is beyond the scope of this standard. The design of active cables shall operate with the transmitter and receiver defined in section 5.3 of this standard. 5.2.7.2 Active connectors 5.2.7.2.1 SAS 4x active connectors 5.2.7.2.1.1 SAS 4x active plug connector
The SAS 4x active cable plug connector is the connector defined in 5.2.3.3.1.1) and shown in figure 74. 5.2.7.2.1.2 SAS 4x active receptacle connector
The SAS 4x active receptacle connector is the connector defined in 5.2.3.3.1.1 and shown in figure 75. 5.2.7.2.1.3 SAS 4x active connector pin assignments
Table 57 defines the pin assignments for SAS 4x cable plug connectors (see 5.2.7.2.1.1) and SAS 4x receptacle connectors (see 5.2.7.2.1.2) for applications using one, two, three, or four of the physical links. Table 57 -- SAS 4x active connector pin assignments and physical link usage Pin usage based on number of physical links supported by the cable assembly a One Rx 0+ Rx 0Rx 1+ Rx 1Rx 2+ Rx 2Rx 3+ Rx 3Tx 3Tx 3+ Tx 2Tx 2+ Tx 1Tx 1+ Tx 0Tx 0+ Sense-3.3V Vcc SIGNAL GROUND CHASSIS GROUND
a Signal Two S1 S2 S3 S4 N/C N/C N/C N/C N/C N/C N/C N/C S13 S14 S15 S16 Three S1 S2 S3 S4 S5 S6 N/C N/C N/C N/C S11 S12 S13 S14 S15 S16 G7 G8 Four S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 S16 S1 S2 N/C N/C N/C N/C N/C N/C N/C N/C N/C N/C N/C N/C S15 S16 G1 ­ G6, G9 Housing N/C = not connected SIGNAL GROUND shall not be connected to CHASSIS GROUND in the connector when used in a cable assembly. 5.2.7.2.2 Mini SAS 4x active connectors 5.2.7.2.2.1 Mini SAS 4x active cable plug connector
The Mini SAS 4x active cable plug connector is the free (plug) 26-circuit Shielded Compact Multilane connector defined in SFF-8088. In order to ensure that active cables are not intermateable with passive receptacles, differentiating keying shall be provided by removing all the key slots from the plug connector and all the keys on the receptacle connector. In addition, two triangle icons on each side on the plug connector shall be added to the plug connector to identify an active cable assembly. These key positions and icons are summarized in Table 58. Table 58 -- Mini SAS 4x active cable plug connector icons and key slot positions Use Icon Key slot positions None Reference Figure 98 End of a SAS external cable that attaches to an end device, 2 Triangles or an enclosure universal port Figure 98 shows an active mini SAS 4x cable plug connector that attaches to an enclosure universal port: Triangle icon for active cable Figure 98 -- Mini SAS 4x cable plug connector that attaches to an enclosure universal port 5.2.7.2.2.2 Mini SAS 4x active receptacle connector
The Mini SAS 4x active receptacle connector is the fixed (receptacle) 26-circuit Shielded Compact Multilane connector defined in SFF-8088 and shown in figure 79. In order to ensure that active cables are not intermateable with passive receptacles, differentiating keying shall be provided by removing all the key slots from the plug connector and all the keys on the receptacle connector. In addition, two triangle icons shall be placed near the receptacle to identify active receptacle connectors. These key positions and icons are summarized in Table 59. Table 59 -- Mini SAS 4x active cable receptacle connector icons and key slot positions Use End device or enclosure universal port Icon 2 Triangles Key positions None 5.2.7.2.2.3 Mini SAS 4x active connector pin assignments
Table 60 defines the pin assignments for Mini SAS 4x cable plug connectors (see 5.2.7.2.2.1) and Mini SAS 4x receptacle connectors (see 5.2.7.2.2.2) for applications using one, two, three, or four of the physical links.
Table 60 -- Mini SAS 4x active connector pin assignments and physical link usage Pin usage based on number of physical links supported by the cable assembly a One Two Three Four A2 A3 N/C N/C N/C N/C N/C N/C B2 B3 N/C N/C N/C N/C N/C N/C A2 A3 A5 A6 N/C N/C N/C N/C B2 B3 B5 B6 N/C N/C N/C N/C B10 B13 A1, A4, A7, A10, A13, B1, B4, B7 Housing N/A First A2 A3 A5 A6 A8 A9 N/C N/C B2 B3 B5 B6 B8 B9 N/C N/C A2 A3 A5 A6 A8 A9 A11 A12 B2 B3 B5 B6 B8 B9 B11 B12 Mating level Signal Rx 0+ Rx 0Rx 1+ Rx 1Rx 2+ Rx 2Rx 3+ Rx 3Tx 0+ Tx 0Tx 1+ Tx 1Tx 2+ Tx 2Tx 3+ Tx 3Sense 3.3 V Vcc
SIGNAL GROUND CHASSIS GROUND Third N/C = not connected a SIGNAL GROUND shall not be connected to CHASSIS GROUND in the connector when used in a cable assembly. 5.2.7.3 Active cable power requirements 5.2.7.3.1 Active cable power overview
Active SAS 4x and Mini SAS 4x cables may contain integrated active devices (e.g. drivers, repeaters, equalizers, as well as electro-optical converters and optical transceivers for fiberoptic assemblies). In order to enable the operation of active devices, 3.3 V power supply is provided. Because active SAS 4x and Mini SAS 4x receptacle connectors must be intermateable with passive cables, sense pins are defined in order to avoid shorting the power supply (see Tables 57 and 60) . The sense pins enable the power supply circuitry to turn on only when an active cable assembly is present, and to remain in the default off state when a passive cable or no cable is present. An example of a power supply logic circuitry design is provided in Annex M. 5.2.7.3.2 Power supply requirements
The voltage and current requirements for the power supply are such as to enable support for active cable assemblies with power consumption at 3.3 V of up to 1 W per each end of the cable with four functioning links. These requirements are summarized in Table 61.
Table 61 -- Active cable power supply requirements Characteristic Units Minimum Nominal Maximum Supply Voltage V 3.135a 3.3 3.465b Supply Current mA 319.4c Current Consumption mA 288.6d Power Consumption mW 1000d,e a At maximum current b The power supply shall not exceed this value at any current c The power supply shall deliver this amount of current at the minimum voltage of 3.135 V. d Maximum consumption for each end of the active cable assembly at the maximum voltage of 3.465V. e This is a derivative quantity obtained from: (maximum supply voltage) x (maximum current consumption) 5.2.7.3.3 Voltage Sense
The active cable assembly shall provide a connection of the Sense pin to ground via a 5 kohm resistor (with tolerance ±5%). The active cable power supply circuitry shall enable power to the receptacle connector only when the presence of the Sense resistor is detected, and it shall be disabled if the Sense pin is open (i.e. no cable plugged in) or shorted to ground (i.e. passive cable). 5.2.7.3.4 Short Circuit Protection
The active cable power supply shall have protection against the connection of the Vcc pin to ground or over-current loading, and shall limit the output current when the equivalent load resistance is less than 1 Ohm. 5.2.7.3.5 Hot-pluggable operation
In order to support hot plugging, the active cable power supply circuitry shall be able to detect the Sense resistor value and provide full current within 50 ms of cable connection. 5.2.7.3.6 Bypassing
The active cable power pins (i.e. Vcc and Sense) shall be coupled to ground via bypass capacitors so that they possess low impedance to ground from 100 MHz to 1.5 times the fundamental frequency of the maximum baud rate supported by the device. These bypassing capacitors shall be present both in the receptacle and the plug. 5.2.7.3.7 Capacitive coupling
In addition to bypassing, the power planes of the printed circuit board on the receptacle side shall be sufficiently coupled to ground. 5.2.7.3.8 Voltage Converters (DC-to-DC)
In implementations where the active circuitry in the cable requires voltages other than the provided 3.3 V, local voltage regulators may be used. These regulators shall be located within the active cable assembly. Annex M
(informative) Active Cable Power Supply and Voltage Detection Circuitry
Powered mini-SAS devices supporting active cables need to operate with passive cables which have the Vcc pin tied to ground. Hence there needs to be a mechanism that turns on the power to the receptacle only when an active cable is plugged in, to avoid shorting the power supply. A voltage sense pin is implemented to detect if an active cable is in operation. This can also be used to detect the status a specific port, or implement other features within a switch device. Fig M1 is an example design utilizing a dual comparator to determine from the sense pin on the active cable plug if an active cable is in operation. The circuit then supplies power based upon whether there is an active cable connected to the receptacle. Figure M.1 -- Dual comparator design for active cable detection The power supply characteristics are specified in Table 61. The type of power delivery device may either be a switching or a linear regulator.