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8 Registers
In Serial ATA, the host adapter contains a set of registers that shadow the contents of the traditional device registers,
referred to as the Shadow Register Block. Shadow Register Block registers are interface registers used for delivering
commands to the device or posting status from the device. Refer to the Serial ATA Specification for details.
In the following cases, the host adapter sets the BSY bit in its Shadow Status Register and transmits a FIS to the
device containing the new contents.
- Command register is written in the Shadow Register Block
- Device Control register is written in the Shadow Register Block with a change of state of the SRST bit
3) COMRESET is requested
8.1 Alternate Status Register
Table 22 Alternate Status Register
Alternate Status Register
7
6
5
4
3
2
1
0
BSY
RDY
DF
DSC/SERV
DRQ
COR
IDX
ERR
This register contains the same information as the Status Register. The only difference is that reading this register
does not imply interrupt acknowledge or clear a pending interrupt. See Section 8.11 for the definition of the bits in this
register.
8.2 Command Register
This register contains the command code being sent to the device. Command execution begins immediately after this
register is written. The command set is shown Section 12.
All other registers required for the command must be set up before writing the Command Register.
8.3 Cylinder High Register
This register contains the high order bits of the starting cylinder address for any disk access. At the end of the
command, this register is updated to reflect the current cylinder number.
This register contains LBA Bits 16-23. At the end of the command, this register is updated to reflect the current LBA
Bits 16-23.
The cylinder number may be from zero to the number of cylinders minus one.
When 48-bit addressing commands are used, the “most recently written” content contains LBA Bits 16-23, and the
“previous content” contains Bits 40-47. The 48-bit Address feature set is described in Section 10.11.
48
Hard Disk Drive Specification