3.3.3.19. SATA¶

Introduction

Serial ATA (Advance Technology Attachment)(SATA) is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives and optical drives. Serial ATA[2] replaces the older AT Attachment standard (ATA later referred to as Parallel ATA or PATA), offering several advantages over the older interface: reduced cable size and cost (seven conductors instead of 40), native hot swapping, faster data transfer through higher signalling rates, and more efficient transfer through an (optional) I/O queuing protocol.

Acronyms & Definitions

Acronym	Definition
SATA	Serial Advanced Technology Attachement
PATA	Parallel AT Attachement
SSD	Solid State Disk
HDD	Hard Disk Drive
Gen-1/Gen-2/Gen-3	Generation of SATA device.

Features NOT supported

Following features are not supported currently:

Gen-3 SATA HDD/SSD is not guaranteed to be supported on OMAP5 and DRA7 due to a silicon bug which prevents correct PHY speed negotiation.
Aggressive Power management

Supported EVMs

EVM	Number of Instances
AM57 GP EVM	1 Instance (either eSATA or mSATA)
Beagle X15	1 Instance (eSATA)
DRA74 GP EVM	1 Instance (SATA)

Table: caption

Kernel Configuration

Device Drivers  --->
    <M> Serial ATA and Parallel ATA drivers (libata)  --->
        <M>   AHCI SATA support
        <M>   Platform AHCI SATA support

Accessing SATA Hard Drive

These instructions assume the SATA hard drive being used has already been partitions. Information on partition the hard drive is beyond the scope of this article.

Kernel

Detecting Hard Drive

Before you can start reading and writing to a partition you first need to know which sdX device is associate with the hard drive. The easiest approach is to use “parted -l”.

This command will show all the various storage medias Linux has detected. The output that will be shown may be quite large if you have sd cards, eMMC, USB thumbdrives, etc.. connected to the board. However, for SATA your only interested in devices that have “(scsi)” at the end of the Model field.

Example output of the command is shown below. Non SATA related output was truncated.

root@am57xx-evm:~# parted -l
...
Model: ATA PLEXTOR PX-64M6M (scsi)
Disk /dev/sda: 64.0GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags:

Number  Start   End     Size    Type     File system  Flags
 1      1049kB  83.9MB  82.8MB  primary  fat32        boot, lba
 2      84.9MB  17.3GB  17.2GB  primary  fat32
 3      17.3GB  64.0GB  46.8GB  primary  ext2
...

Above the model field shows the name of the particular hard drive and in the disk field it shows the specific device (/dev/sdX) its associated with along with the size. In the above example this Plextor hard drive is associated with “/dev/sda”. The other additional information that can be gathered from the parted -l command is information regarding the various partitions. In the table that has column Number, Start, End, etc... you can see this hard drive has 3 partitions. The command shows various information including the partition size along with the file system type.

This is useful since each partition can be accessed via /dev/sdXY. Where X is the specific disk letter and Y is the partition number. Therefore, the device that is associated with the Plextor hard drive’s second partition is “/dev/sda2” which is a ~17GB FAT32 partition.

Determining Mounted Partition Location

Now its likely if you have partitions on the hard drive that their already been automated. Use “lsblk /dev/sdX” to determine if a partition has been mounted and if so where.

Example output of the command is shown below:

root@am57xx-evm:~# lsblk /dev/sda
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda      8:0    0 59.6G  0 disk
|-sda2   8:2    0   16G  0 part /run/media/sda2
|-sda3   8:3    0 43.6G  0 part
`-sda1   8:1    0   79M  0 part /run/media/sda1

The above output shows the three sda partitions. Under mountpoint it list the directory that the partition has been mounted to. However, a blank entry under mount point indicates the partition has not been mounted.

U-Boot

Information regarding accessing SATA hard drive in U-boot can be found in the Linux Core U-boot User’s Guide SATA Section.