HP Q153090901 3Ch, READ BUFFER

READ BUFFER 3Ch

READ BUFFER reads data from the memory on the drive and sends it to the initiator. The value of the Mode field determines whether only the 4-byte descriptor is returned, only the data is returned, or whether both are returned.

Pre-execution checks:

Illegal Field Reservation Deferred Error Unit Attention

If any of the following rules are broken then CHECK CONDITION status is reported. Sense data will be as described in Illegal Field Checks.

Command descriptor block:

	7		6	5	4		3	2	1	0
0					Operation	Code (3Ch)
1		Reserved(0)						Mode
2					Buffer ID
3	(MSB)				Buffer Offset
5										(LSB)
6	(MSB)				Allocation Length
8										(LSB)
9					Control

CDB fields:

Mode	00000b A 4-byte descriptor is returned, followed by (Allocation Length − 4) bytes of data.The data
		is read from the buffer identified by the Buffer ID, starting from offset zero in the buffer.
		The Buffer ID and Buffer Offset must both be 00h.
	00010b	The drive returns Allocation Length bytes of data which is read from the buffer identified
		by the Buffer ID, starting from Buffer Offset bytes from the start of the buffer.
		There are no restrictions on the value of Buffer ID and Buffer Offset, except that the Buffer
		Offset must be kept within the buffer size.
	00011b	The drive returns a 4-byte descriptor for the buffer identified by the Buffer ID field. Invalid
		buffer IDs will return a buffer descriptor of all zeros.
		The Buffer Offset field must be zero.
	01010b	The drive returns data from the Echo Buffer. The Buffer ID and Offset are ignored.
	01011b	The drive returns the Echo Buffer descriptor. The Buffer ID and Offset are ignored.

Buffer ID The Buffer ID indicates which buffer is to be read. The buffers are defined as follows:

Buffer ID Memory Area		Category	Offset Boundary
00h	Main buffer memory	RAM	4 bytes
01h	Processor addressable memory	RAM	1 byte

Commands

READ BUFFER 3Ch 121