Mechanism

The enclosure management for SATA Controller involves sending messages that control LEDs in the enclosure. The messages for this function are stored after the normal registers in the AHCI BAR, at Offset 580h bytes for the PCH from the beginning of the AHCI BAR as specified by the EM_​LOC global register.

Software creates messages for transmission in the enclosure management message buffer. The data in the message buffer should not be changed if CTL.TM bit is set by software to transmit an update message. Software should only update the message buffer when CTL.TM bit is cleared by hardware otherwise the message transmitted will be indeterminate. Software then writes a register to cause hardware to transmit the message or take appropriate action based on the message content. The software should only create message types supported by the controller, which is LED messages for the PCH. If the software creates other non LED message types (such as, SAF-TE, SES-2), the SGPIO interface may hang and the result is indeterminate.

During reset all SGPIO pins will be in tri - state state. The interface will continue staying in tri - state state after reset until the first transmission occurs, when software programs the message buffer and sets the transmit bit CTL.TM. The SATA host controller will initiate the transmission by driving SCLOCK and at the same time driving the SLOAD to “0” prior to the actual bit stream transmission. The Host will drive SLOAD low for at least 5 SCLOCK then only start the bit stream by driving the SLOAD to high. SLOAD will be driven high for 1 SCLOCK, followed by vendor-specific pattern that is default to “0000” if software is yet to program the value. A total of 24-bit streams from 8 ports (Port 0, Port 1, Port 2, Port 3, Port 4, Port 5, Port 6, Port 7) of 3-bit per port LED message will be transmitted on SDATAOUT0 pin after the SLOAD is driven high for 1 SCLOCK. For 8 SATA port configuration, only 4 ports (port 4, port 5, port 6 and port 7) of 12 bit total LED message follow by 12 bits of tri-state value will be transmitted out on SDATAOUT1 pin. For 6 SATA port configuration, only 2 ports (port 4 and port 5) of 6 bit total LED message follow by 18 bits of tri-state value will be transmitted out on SDATAOUT1 pin. For 4 SATA port configuration, SDATAOUT1 pin is not required hence can be tri-state always.

All the default LED message values will be high prior to software setting them, except the Activity LED message that is configured to be hardware driven that will be generated based on the activity from the respective port. All the LED message values will be driven to ‘1’ for the port that is unimplemented as indicated in the Port Implemented register regardless of the software programmed value through the message buffer.

There are 2 different ways of resetting the PCH’s SGPIO interface, asynchronous reset and synchronous reset. Asynchronous reset is caused by platform reset to cause the SGPIO interface to be tri-state asynchronously. Synchronous reset is caused by setting the CTL.RESET bit, or HBA reset, where Host Controller will complete the existing full bit stream transmission then only tri-state all the SGPIO pins. After the reset, both synchronous reset and asynchronous reset, the SGPIO pins will stay tri-stated.

Message Format

Messages shall be constructed with a one DWord header that describes the message to be sent followed by the actual message contents. The first DWord shall be constructed as shown in Enclosure Management Message Format (EM_​MF) register, refer to PCH-LP Datasheet Volume 2.

The SAF-TE, SES-2, and SGPIO message formats are defined in the corresponding specifications, respectively. The LED message type is defined in the Enclosure Management LED (EM_​LED) register, refer to PCH-LP Datasheet Volume 2. It is the responsibility of software to ensure the content of the message format is correct. If the message type is not programmed as 'LED' for this controller, the controller shall not take any action to update its LEDs. For LED message type, the message size always consists of 4 bytes.

LED Message Type

The LED message type specifies the status of up to three LEDs. Typically, the usage for these LEDs is activity, fault, and locate. Not all implementations necessarily contain all LEDs (for example, some implementations may not have a locate LED). The message identifies the HBA port number and the Port Multiplier port number that the slot status applies to. If a Port Multiplier is not in use with a particular device, the Port Multiplier port number shall be ‘0’. The format of the LED message type is defined in the Enclosure Management LED (EM_​LED) register, refer to PCH-LP Datasheet Volume 2. The LEDs shall retain their values until there is a following update for that particular slot.

SGPIO Waveform