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An Overview of Serial ATA Technology

An Overview of Serial ATA Technology. Chris Erickson Graduate Student Department of Electrical and Computer Engineering Auburn University, Auburn, AL 36849 Chris.Erickson@auburn.edu. Objectives. Why SATA was invented The differences between PATA and SATA

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An Overview of Serial ATA Technology

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  1. An Overview of Serial ATA Technology Chris Erickson Graduate Student Department of Electrical and Computer Engineering Auburn University, Auburn, AL 36849 Chris.Erickson@auburn.edu

  2. Objectives • Why SATA was invented • The differences between PATA and SATA • How the hardware is structured to transmit and receive SATA • Protocol of SATA transmission

  3. What is PATA? • All of the below synonyms refer to a modern day PATA drive • PATA – Parallel Advanced Technology Attachment • UDMA – Ultra Direct Memory Access • IDE – Integrated Device Electronics • EIDE – Enhanced IDE

  4. More on PATA • 40 & 80 wire cable option • 40 wire limited to UDMA 33 MB/s and below • 80 wire allowed for UDMA 66, 100, 133 MB/s • Required by ATA spec to be 5v tolerant (3.3v has been the norm for several years) • Must support Master/Slave/Cable Select

  5. SATA Basics • New Connector • Saves space • More reliable • More air flow • Connector has 4 transmission wires • Tx differential pair • Rx differential pair

  6. SATA Basics • SATA I for 1.5Gbps ~ 150MB/s • SATA II for 3.0Gbps ~ 300MB/s • Provides support for legacy command set • Includes new commands for SATA BIST and power management

  7. Connectivity • Serial ATA is point-to-point topology • Hosts can support multiple devices but requires multiple links • 100% available link bandwidth • Failure of one device or link does not affect other links

  8. Link Characteristics • SATA uses full-duplex links • Protocol only permits frame transfer in one direction at a time • Each link consists of a transmit and a receive pair • SATA uses low voltage levels • Nominal voltage +/-250mV differential

  9. Power Management • SATA has • Phy Ready – Capable of sending and receiving data. Main phase locked loop are on and active • Partial – Physical layer is powered but in a reduced state. Must be able to return to Phy Ready within 10 us. • Slumber – Physical layer is powered but in a reduced state. Must be able to return to Phy Ready within 10 ms. • ATA also defines IDLE, STANDBY, and SLEEP • Necessary for newer laptop & mobile devices

  10. Host Control Software Buffer Memory DMA management Device Control Software Buffer Memory DMA management Serial digital transport control Serial digital transport control Serial digital link control Serial digital link control Serial physical interface Serial physical interface Host Layers Device Layers SATA Architectural Model Application Transport Link Physical

  11. Physical Layer • Transmission (Tx) and Reception (Rx) of a 1.5Gb/s serial stream • Perform power on sequencing • Perform speed negotiation • Provide status to link layer • Support power management requests • Out-of-Band (OOB) signal generation and detection

  12. Out of Band • Part of normal power on sequence • Allows host to issue a device hard reset • Allows device to request a hard reset • Brings device out of low power state

  13. Out of Band Signals • COMRESET • Always originated by the host • Forces a hard reset in the device • Used to start link initialization • COMINIT • Always originated by the device • Requests a link reset • Issued by device in response to COMRESET

  14. Out of Band Signals (cont.) • COMWAKE • Can be originated by either host or device • Used as final phase of OOB initialization • Used to bring out of low power & test states • Exit Partial • Exit Slumber • Exit BIST

  15. Out of Band Signal Forms COMRESET / COMINIT 320 ns 106.7 ns COMWAKE 106.7 ns 106.7 ns

  16. Out of Band Signaling Protocol COMRESET COMINIT Host Device COMWAKE COMWAKE

  17. SATA Port Model Tx + Serializer Data In Tx - Align Generator Tx Clock Phy Reset Port Control Logic Phy Ready Analog Front End Slumber Partial SPD Select SPD Mode System Clock Deserializer Rx + Data Out Clock & Data Recovery Rx - OOB Detect RX Clock COMRESET / COMINIT COMWAKE

  18. Host Control Software Buffer Memory DMA management Device Control Software Buffer Memory DMA management Serial digital transport control Serial digital transport control Serial digital link control Serial digital link control Serial physical interface Serial physical interface Host Layers Device Layers SATA Architectural Model Application Transport Link Physical

  19. Link Layer • 8b / 10b encoding • Scrambles and descrambles data and control words • Converts data from transport layer into frames • Conduct CRC generation and checking • Provides frame flow control

  20. Encoding Concepts • All 32 bit Dwords are encoded for SATA • 32 bits data = 40 bits of transmission • Provides sufficient transition density • Guarantees transition (0s and 1s) even if data is 0x00 or 0xFF • Provides an easy way to detect transmission error

  21. Current Running Disparity (CRD) • As each character is encoded a count is maintained of the number of 0’s and 1’s being transmitted • More 1’s than 0’s give positive disparity • More 0’s than 1’s gives negative disparity • Same number gives neutral disparity • Only valid values of CRD are -1 and 1 • Any other value indicates that a transmission error has occurred

  22. CRD+ & CRD- Encoded Characters 8b Character 0x3F 0 0 1 1 1 1 1 1 This 10b Character transmitted when CRD negative This 10b Character transmitted when CRD positive 1 0 1 0 1 1 1 0 0 1 0 1 0 1 0 0 1 0 0 1 This character 6 ones 4 zeros Disparity +2 This character 4 ones 6 zeros Disparity -2

  23. SATA Primitives • Convey real-time state information • Control transfer of information between host and device • Provide host/device coordination

  24. SATA Primitives • ALIGN – Speed negotiation and at least every 256 Dword • SYNC – Used when in idle to maintain bit synchronization • CONT – Used to suppress repeated primitives

  25. SATA Primitives • X_RDY • R_RDY • R_IP • R_OK • R_ERR • SOF • EOF • HOLD • HOLDA

  26. SATA Frame Structure • All SATA frames consist of: • A start of frame (SOF) delimiter • A payload – transport layer information • A Cyclic Redundancy Check (CRC) • An end of frame (EOF) delimiter SOF Payload Data CRC EOF

  27. SYNC SYNC SYNC SYNC SYNC SYNC SYNC SYNC SYNC SYNC SYNC SYNC Link Layer Protocol (1) Host Device

  28. SYNC SYNC X_RDY X_RDY X_RDY X_RDY SYNC SYNC SYNC SYNC SYNC SYNC Link Layer Protocol (2) Host Device

  29. X_RDY X_RDY X_RDY X_RDY X_RDY X_RDY SYNC R_RDY R_RDY R_RDY R_RDY SYNC Link Layer Protocol (3) Host Device

  30. X_RDY X_RDY SOF DATA DATA DATA R_RDY R_RDY R_RDY R_RDY R_RDY R_RDY Link Layer Protocol (4) Host Device

  31. DATA DATA DATA DATA DATA DATA R_RDY R_IP R_IP R_IP R_IP R_RDY Link Layer Protocol (5) Host Device

  32. DATA DATA CRC EOF WTRM WTRM R_IP R_IP R_IP R_IP R_IP R_IP Link Layer Protocol (6) Host Device

  33. CRC EOF WTRM WTRM WTRM WTRM R_IP R_IP R_IP R_IP R_IP R_IP Link Layer Protocol (7) Host Device

  34. WTRM WTRM WTRM WTRM WTRM WTRM R_IP R_OK R_OK R_OK R_OK R_IP Link Layer Protocol (8) Host Device

  35. WTRM WTRM SYNC SYNC SYNC SYNC R_OK R_OK R_OK R_OK R_OK R_OK Link Layer Protocol (9) Host Device

  36. SYNC SYNC SYNC SYNC SYNC SYNC R_OK SYNC SYNC SYNC SYNC R_OK Link Layer Protocol (last) Host Device

  37. Host Control Software Buffer Memory DMA management Device Control Software Buffer Memory DMA management Serial digital transport control Serial digital transport control Serial digital link control Serial digital link control Serial physical interface Serial physical interface Host Layers Device Layers SATA Architectural Model Application Transport Link Physical

  38. Transport Layer • Responsible for the management of Frame Information Structures (FIS) • At the command of Application layer: • Format the FIS • Make frame transmission request to Link layer • Pass FIS contents to Link layer • Receive transmission status from Link layer and reports to Application layer

  39. Frame Information Structure (FIS) • A FIS is a mechanism to transfer information between host and device application layers • Shadow Register Block contents • ATA commands • Data movement setup information • Read and write data • Self test activation • Unique FIS Type Code

  40. FIS types

  41. Register – Host to Device FIS

  42. BIST Activate FIS T - Far end transmit only – transmit Dwords defined in words 1 & 2 A - No ALIGN transmission (valid only with T) S - Bypass scrambling (valid only with T) L - Far end retimed loopback with ALIGN insertion F - Far end analog loopback P - Transmit primitives defined in words 1 & 2 of the FIS R - Reserved V - Vendor Unique Test Mode – other bits undefined

  43. Data FIS

  44. Host Control Software Buffer Memory DMA management Device Control Software Buffer Memory DMA management Serial digital transport control Serial digital transport control Serial digital link control Serial digital link control Serial physical interface Serial physical interface Host Layers Device Layers SATA Architectural Model Application Transport Link Physical

  45. Command / Application Layer • Defined using a series of state diagrams • Register H  D • Register D  H • DMA data in • DMA data out • Host command layer may be the same but may only support legacy commands

  46. Completed !! • Any Question? Comments?

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