Methods and structure for hardware serial advanced technology attachment (SATA) error recovery in a serial attached SCSI (SAS) expander

A method operable in a Serial Attached SCSI (SAS) expander, the expander having one or more host physical links (PHYs) each coupled with a corresponding Serial Advanced Technology Attachment (SATA) Tunneling Protocol (STP) initiator device and having a target PHY directly coupled to a SATA end device, the expander having a programmable controller and a control circuit separate from the programmable controller, the method comprising:

• receiving, at a host PHY of the expander, a request from an STP initiator device to establish a connection to the SATA end device through the target PHY;
• establishing the requested connection between the host PHY and the target PHY through an intermediate buffer of the expander, wherein the connection is established by operation of the programmable controller;
• storing one or more commands received from the STP initiator device in the buffer for later transmission to the end device, wherein the commands are received and stored in the buffer by operation of the control circuit;
• detecting receipt of an error status from the SATA end device, wherein the error status is received and detected by operation of the control circuit;
• and
• communicating with the STP initiator device and with the SATA end device to clear the detected error status, wherein the communications are performed by operation of the control circuit without involvement of the programmable controller.

A method operable in a Serial Attached SCSI (SAS) expander, the expander having one or more host physical links (PHYs) each coupled with a corresponding Serial Advanced Technology Attachment (SATA) Tunneling Protocol (STP) initiator device and having a target PHY directly coupled to a SATA end device, the expander having a programmable controller and a control circuit separate from the programmable controller, the control circuit comprising a SATA host circuit coupled with the target PHY, the control circuit further comprising a SATA target circuit coupled with each of the one or more host PHYs, the control circuit further comprising a buffer coupled with the SATA target circuit and coupled with the SATA host circuit, the method comprising:

• establishing, by operation of the programmable controller, a connection between any of the one or more STP initiator devices and the SATA end device;
• storing, by operation of the SATA target circuit, in the buffer commands received from any of the one or more STP initiator device;
• forwarding, by operation of the SATA host circuit, stored commands from the buffer to the SATA end device;
• detecting, by operation of the SATA host circuit, receipt of an error status from the SATA end device;
• responsive to detecting receipt of the error status, determining, by operation of the control circuit, a first portion of the one or more STP initiator devices that have commands stored in the buffer and a second portion of the one or more STP initiator devices that do not have commands stored in the buffer;
• storing, by operation of the SATA target circuit, further commands in the buffer from any of the STP initiator devices in the second portion;
• rejecting, by operation of the SATA target circuit, any further commands received from any of the STP initiators in the first portion until the error status is cleared;
• and
• clearing, by operation of the control circuit, the detected error status without involvement of the programmable controller.