SAT Article
This SAT article features information on SAT. The article will explain what SAT is, if you need it, and if your controller supports among other things.
SAT (SCSI->ATA Translation) is a mechanism whereby ATA task register commands may be sent to a device which is seen by the operating system as a SCSI device. This is most often the case when SATA drives are connected to an add-in PCI bus type of SATA controller card. Even though the card is a SATA controller in most cases Windows will see the controller as if it were a SCSI HBA, and so will not allow you to issue ATA task register level commands to the connected devices.
Contents of Article
What is SAT?
How do I know that I need to use SAT?
Does my controller card support SAT?
A Simple test command
Issuing the ATA SMART command
Details of defining an IDENTIFY command
Details of defining a SMART command
Conclusion
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Ask Dr. SCSI – “When I do a BAM trace, I see a lot of SRB phase types. How do I interpret the information displayed in the SRB phase?”
Q. “When I do a BAM trace, I see a lot of SRB phase types. How do I interpret the information displayed in the SRB phase?”
A. “The first 16 bytes of the SRB have the following information:
Bytes 0-thru-1: Length
Byte 2: Function
Byte 3 bits 0-thru-5: SRB Status
Byte 3 bit 6: Queue-frozen bit
Byte 3 bit 7: Auto-sense valid bit
Byte 4: Scsi Status
Byte 5-thru-7: PathID,TargetID,Lun
Byte 8-thru-9: QueueTag,QueueAction
Byte 10: CDB Length
Byte 11: Sense Info Buffer Length
Byte 12: SRB Flags
Let’s take a look at the following SRB phase:
The Length field is hex ’40 00’ or decimal 64.
The Function field is ‘00’: some of the most common values for this field are
0 = SRB_FUNCTION_EXECUTE_SCSI
4 = SRB_FUNCTION_RELEASE_QUEUE
The SRB Status field is ‘01’: some of the most common values for this field are
1 = SRB_STATUS_SUCCESS
2 = SRB_STATUS_ABORTED
4 = SRB_STATUS_ERROR
‘0A’ = SRB_STATUS_SELECTION_TIMEOUT
‘12’ = SRB_STATUS_DATA_OVERRUN
The Scsi Status field at byte 4 is ‘00’ – this indicates there was no check condition. If the field is ‘02’ then the target issued a check condition (so there would be sense data available to evaluate)
The PathID,TargetID,Lun fields at bytes 5,6,7 are ’00 01 00’ – this means PathID = 0, TargetID = 1, Lun = 0. Notice these are indicated under the “Device” column
The CDB Length field at byte 10 is ‘06’. Notice the command that was issued was an Inquiry command and this command is 6-bytes long.
The Sense Info Buffer Length field at byte 11 is ‘80’ or decimal 128
Now let’s take a look at an SRB associated with a command where the target rejects the command. In the below output, the Device 5:0:0:0 is a disk drive and we are attempting to send it a library command “Read Element Status”. It rejects the command with a check condition and sends the sense data.
Look at byte 3 – it is hex ‘84’. Bits 0-thru-5 are hex ‘04’, bit 6 is 0, bit 7 is 1. The interpretation of this is the SRB Status is 4 (srb status error), and the AutoSense Valid bit is 1.
Notice that the Scsi Status field is ‘02’ – this indicates the target issued a check condition.
The CDB Length is ‘0C’ or decimal 12 and the Read Element Status command is 12-bytes long.
The Sense Info Buffer Length is ‘12’ or decimal 18 – the driver in this case only provided an 18-byte buffer for sense data. Note that many devices may return much more sense data than 18 bytes!!
The following example is quite interesting – a “Mode Sense” command was issued with a buffer that has 255-bytes available but the target only has 12 bytes to return. Here we see two SRBs associated with this command (in the “Ctr” column these SRBs are Ctr=45 and Ctr=45)
In the SRB on Ctr = 44, at byte 3 we see ‘52’ so bits 0-thru-5 is ‘12’ which is an SRB Status of SRB_STATUS_DATA_OVERRUN. Notice also that the Scsi Status at byte 4 is 0 (i.e. no error) so this is a completely normal event.
In the SRB on Ctr = 45, we see some oddities: Normally the Function field at byte 2 is ‘00’ but this time it is ‘04’ or SRB_FUNCTION_RELEASE_QUEUE. Almost always a data overrun SRB has a corresponding release queue SRB.
In our final example, a “Test Unit Ready” command is issued and we have two SRBs associated with the command.
At Ctr = 14 we have the first of the two SRBs – the SRB Status (at byte 3 bit 0-thru-5) is ‘0A’ or Selection Timeout. The Queue Frozen bit is also ‘1’. Notice that in the following SRB (Ctr = 15) we see a “release queue” SRB.
Issuing ATA/SATA Commands Article
Here’s another exclusive article from STB including what is involved with issuing ATA/SATA Commands.
ATA commands, also referred to as ATA task register commands, are commands issued to ATA or SATA interface storage devices. From now on in this article when we refer to ATA we mean this to include both ATA and SATA devices.
ATA commands are used to write and read data from ATA drives, as well as to set various device parameters and to read device health data.
Task registers refers to the original hardware interface to these devices which consisted of seven separate registers. These seven registers were loaded with the appropriate values and were then transferred to the drive, where the drive would interpret from the registers what it was being asked to do, and would then (hopefully) complete the command.
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