Specifications

ATAPI For Streaming Tape QIC-157 Rev B

6.8.11. REQUEST SENSE Command

The REQUEST SENSE command requests that the Device transfer sense data to the Host.

Table 6-62 Request Sense Command

Bit

Byte

7 6 5 4 3 2 1 0

0 Operation code (03h)

1 Reserved

2 Reserved

3 Reserved

4 Allocation Length

5 Reserved

6 Reserved

7 Reserved

8 Reserved

9 Reserved

10 Reserved

11 Reserved

The sense data:

1. shall be available if an error condition (“Check Condition”) had previously been reported to the

Host;

2. shall be available if other information (e.g. medium position) is available in any field.

If the Device has no other sense data available to return, it shall return a Sense Key of NO SENSE

and an Additional Sense Code of NO ADDITIONAL SENSE INFORMATION.

The sense data shall be preserved by the Device until retrieved by a REQUEST SENSE command

or until the receipt of any other I/O Command.

The Device shall return “Check Condition” status for a REQUEST SENSE command only to report

exception conditions specific to the command itself. For example:

1. A non-zero reserved bit is detected in the Command Packet;

2. A Device malfunction prevents return of the sense data.

If a recovered error occurs during the execution of the REQUEST SENSE command, the Device

shall return the sense data with “Good” status. If a Device returns “Check Condition” status for a

REQUEST SENSE command, the sense data may be invalid.

Devices shall be capable of returning at least 18 bytes of data in response to a REQUEST SENSE

command. If the allocation length is 18 or greater, and a Device returns less than 18 bytes of data,

the Host should assume that the bytes not transferred would have been zeros had the Device

returned those bytes. Host can determine how much sense data has been returned by examining the

allocation length parameter in the Command Packet and the additional sense length in the sense

data. Devices shall not adjust the additional sense length to reflect truncation if the allocation length

is less than the sense data available.

The sense data format for error codes 70h (current errors) and 71h (deferred errors) are defined in

Table 6-63 Request Sense Standard Data. Error code values of 72h to 7Eh are reserved. Error code

7Fh is for a vendor-specific sense data format. Devices shall implement error code 70h;