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Introduction
1344
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Serial ATA (SATA) Controller
28.1 Introduction
During these times, the parallel ATA (PATA) interface has gone through changes to sustain the demands
of the newly emerging applications needs. However, the PATA controller reached a point where it required
major changes to satisfy the upcoming applications requirements and this led to its successor, the birth of
the SATA controller. This device has a built-in SATA controller with a single HBA port operating in
Advanced Host Controller Interface (AHCI) mode and is used to interface to data storage devices at both
1.5 Gbits/second and 3.0 Gbits/second line speeds. AHCI describes a system memory structure that
contains a generic area for control and status, and a table of entries describing a command list where
each command list entry contains information necessary to program an SATA device, and a pointer to a
descriptor table for transferring data between system memory and the device.
28.1.1 Purpose of the Peripheral
The SATA controller addresses the drawback of the PATA interface architecture, throughput, and protocol
perspectives. PATA required 40/80 wire parallel cable with a length requirement not exceeding 18 inches.
With the current hardware design, PATAs maximum transfer rate saturated to a 133 Mbytes/second of
transfer. In addition to newly added features, like Hot swapping and native command queuing, the SATA
controller abandoned the parallel physical interface and transitioned to a serial format using two differential
pairs supporting up to 3 Gbits/second transfer rate, translating to a 300 Mbytes/second raw throughput.
With the intent on handling the previous and current role of the PATA controller and addressing the future
needs, the SATA controller is architected with the option of operating in a Legacy mode, a mode that
behaves similar to the PATA controller from the protocol/driver perspective, and a new AHCI mode that is
different from the Legacy mode allowing it to overcome the drawbacks of PATA as well as extending
PATAs capabilities. The SATA controller that is supported by this device supports AHCI mode of operation
only. AHCI is a PCI class device that acts as a data movement engine between system memory and serial
ATA devices. However, the AHCI controller on this device is integrated within the core chipset, a common
attribute for embedded devices. The AHCI controller supported has no support for Legacy mode of
operation.
Communication between a device and software moves from the task file via byte-wide accesses to a
command FIS located in system memory that is fetched by the HBA. This reduces command setup time
significantly, allowing for many more devices to be added to a single host controller. Software no longer
communicates directly to a device via the task file. In other words, all data transfers between the device
and system memory occur through the HBA acting as a bus master to system memory. Whether the
transaction is of a DMA type or a PIO type (the use of the PIO command type is strongly discouraged and
all transfers should be performed using DMA unless otherwise that a transaction is only performed via PIO
command), the HBA fetches and stores data to memory, offloading the CPU. There is no accessible data
port. Software written for AHCI is not allowed to utilize any of the legacy mechanisms to program devices.
The SATA controller uses a less massive thinner flexible cable that can be up to 3 feet (1 meter) in length
allowing for easier routing and better air ventilation inside a case. Its power budget is significantly reduced
to 250 mV compared to the required 5V power of PATA.
Like its predecessor, the SATA controller is most commonly used by PCs and portable devices to
interface a host processor with data storage or CD/audio devices. It also has the support for hot swapping
capability. It also supports the use of a Port Multiplier to increase the number of devices that can be
attached to the single HBA port.
28.1.2 Features Supported
The main features of the SATA controller are:
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Synopsis DWH Serial ATA 1.5 Gbps and 3 Gbps speeds core
•
Support for the AHCI controller spec 1.1
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Integrated TI SERDES PHY
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Integrated Rx and Tx data buffers
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Supports all SATA power management features
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Internal DMA engine per port
•
Hardware-assisted native command queuing (NCQ) for up to 32 entries