How to reset SATA Devices(with AHCI architecture) by UEFI shell mm command?

How to get Bar5 address first?

fs0:\test〉 pci

   Seg  Bus  Dev  Func

   ---  ---  ---  ----

    00   04   00    00 ==〉 Mass Storage Controller - UNDEFINED

             Vendor 1B4B Device 9230 Prog Interface 1

fs0:\test〉 pci 4 0 0

pci 4 0 0

  PCI Segment 00 Bus 04 Device 00 Func 00 [EFI 0004000000]

  00000000: 4B 1B 30 92 07 00 10 00-11 01 06 01 08 00 00 00  *K.0.............*

  00000010: 01 EC 00 00 81 E8 00 00-01 E8 00 00 81 E4 00 00  *................*

  00000020: 01 E4 00 00 00 F8 BF FE-00 00 00 00 4B 1B 30 92  *............K.0.*

  00000030: 00 00 BE FE 40 00 00 00-00 00 00 00 0B 01 00 00  *....@...........*

  00000040: 01 50 03 40 00 00 00 00-00 00 00 00 00 00 00 00  *.P.@............*

  00000050: 05 70 00 00 00 00 00 00-00 00 00 00 00 00 00 00  *.p..............*

  00000060: 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00  *................*

  00000070: 10 E0 12 00 02 87 28 00-10 20 09 00 22 3C 03 00  *......(.. .."<..*

  00000080: 40 00 21 10 00 00 00 00-00 00 00 00 00 00 00 00  *@.!.............*

  00000090: 00 00 00 00 10 00 00 00-00 00 00 00 00 00 00 00  *................*

  000000A0: 02 00 01 00 00 00 00 00-00 00 00 00 00 00 00 00  *................*

  000000B0: 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00  *................*

  000000C0: 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00  *................*

  000000D0: 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00  *................*

  000000E0: 12 00 00 00 48 00 00 00-00 00 00 00 00 00 00 00  *....H...........*

  000000F0: 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00  *................*

Bar5=〉0xFEBFF800

[Reset SATA HDDs by shell mm commands]

edit file as below:
#####################################################################

mm febff800 4 ;MMIO -n

mm febff804 4 ;MMIO :0x80000000 -n # ==〉 Enable AHCI

mm febff804 4 ;MMIO -n

#pause

mm febff92c 4 ;MMIO :0x21 -n # ==〉 Reset Port0

stall 100000

mm febff92c 4 ;MMIO :0x20 -n

mm febff92c 4 ;MMIO -n

#pause

mm febff9ac 4 ;MMIO :0x21 -n # ==〉 Reset Port1

stall 100000

mm febff9ac 4 ;MMIO :0x20 -n

mm febff9ac 4 ;MMIO -n

#pause

mm febffa2c 4 ;MMIO :0x21 -n # ==〉 Reset Port2

stall 100000

mm febffa2c 4 ;MMIO :0x20 -n

mm febffa2c 4 ;MMIO -n

#pause

mm febffaac 4 ;MMIO :0x21 -n # ==〉 Reset Port3

stall 100000

mm febffaac 4 ;MMIO :0x20 -n

mm febffaac 4 ;MMIO -n

#pause

#####################################################################

fs0:\〉 test.nsh

ATA IDENTIFY DEVICE Data Table - Nominal media rotation rate(R.P.M)

7.18.7.81 Word 217: Nominal media rotation rate(RPM)

Word 217 indicates the nominal media rotation rate of the device and is defined in table 38.

Table 38 — Nominal Media Rotation Rate

Value	Description
0000h	Rate not reported
0001h	Non-rotating media (e.g., solid state device)
0002h-0400h	Reserved
0401h-FFFEh	Nominal media rotation rate in rotations per minute (rpm) (e.g., 7200 rpm = 1C20h)
FFFFh	Reserved

ATA IDENTIFY DEVICE Data Table

在AHCI上，什麼是BIST與Index-Data Pair?

[AHCI 1.3 -> 10.13] BIST 
BIST是進入，當軟體建立一個BIST FIS在命令列中與設定CTBAz[B]。一但BIST命令被放到列表裡，SW將不允許去建立任何命令直到它清除PxCMD.ST。HBA如何運作的細節在測試模式中，此是章節將不在此說明範圍內。一個晶片商的連續特殊的試驗，可能被執行經由晶片商的特殊定義的戰存器(如同那些在HBA的PCI配置空間)。此BIST的細節不被定義在AHCI中，去允許晶片商自由的建構不是很詳盡的或不是很明顯測試架構。
此測試模式被退出時，是系統軟體清除PxCMD.ST與寫入一個0x01的值到PxSCTL.DET。清除PxCMD.ST放置DMA控制器進入到空閒，與寫PxSCTL.DET去重置此介面。

[AHCI 1.3 -> 10.14] Index-Data Pair
Index-Data  Pair  (IDP)提供主機軟體一個途徑，藉由執行memory mapped I/O space (> 1MB)去讀寫AHCI的暫存器。在PC平台上，主機軟體 (BIOS, Option ROMs, OSs)寫入運作在真實模式(‘real-mode’ (8086 mode))不能存取在配置在PCI上的記憶體位址，如果此位址空間是(1)記憶體映射與(2)映射大於1MB。 AHCI被致能後必須面對的問題：

• AHCI並不支援BIOS IDE存取方式。 
• AHCI實現支援BIOS存取途徑，也支援4個裝置以上(一般或經由擴充器(Port Multiplier))

此IDP的途徑允許主機軟體去存取所有AHCI的MMIO暫存器間接I/O位址，在間接記憶體映射位址的地方存取經由AHCI基本位址暫存器(ABAR)。


當去設計一個驅動程式時，IDP與AHCI’s MMIO registers誰先搶到GHC.AE，並將它設為"1" ，另一端將放棄其控制權，要不然將會有衝突。

[Qemu-devel] [PATCH] ahci: add port I/O index-data pair

http://lists.gnu.org/archive/html/qemu-devel/2011-08/msg03327.html

ATA IDENTIFY DEVICE Data Table

ATA8 IDENTIFY DEVICE Data Table

Word O/M F/V Description   
0 M General configuration bit-significant information:   
F 15 0 = ATA device   
X 14:8 Retired   
F 7 1 = removable media device   
X 6 Obsolete   
X 5:3 Retired   
V 2 Response incomplete   
X 1 Retired   
F 0 Reserved   

1 X Obsolete   

2 O V Specific configuration   

3 X Obsolete   

4-5 X Retired   

6 X Obsolete   

7-8 O V Reserved for assignment by the CompactFlashä Association   

9 X Retired   

10-19 M F Serial number (20 ASCII characters)   

20-21 X Retired   

22 X Obsolete   

23-26 M F Firmware revision (8 ASCII characters)   

27-46 M F Model number (40 ASCII characters)   

47 M F 15:8 80h   
F 7:0 00h = Reserved   
F 01h-FFh = Maximum number of logical sectors that shall be transferred per DRQ data block on READ/WRITE MULTIPLE commands   

48   O     B          Trusted Computing feature set options

F 15  Shall be cleared to zero

F 14  Shall be set to one

13:1  Reserved for the Trusted Computing Group

F 0  1=Trusted Computing feature set is supported


49 M Capabilities   
F 15:14 Reserved for the IDENTIFY PACKET DEVICE command.   
F 13 1 = Standby timer values as specified in this standard are supported   
0 = Standby timer values shall be managed by the device   
F 12 Reserved for the IDENTIFY PACKET DEVICE command.   
F 11 1 = IORDY supported   
0 = IORDY may be supported   
F 10 1 = IORDY may be disabled   
F 9 1 = LBA supported   
F 8 1 = DMA supported.   
X 7:0 Retired   

50 M Capabilities   
F 15 Shall be cleared to zero.   
F 14 Shall be set to one.   
F 13:2 Reserved.   
X 1 Obsolete   
F 0 Shall be set to one to indicate a device specific Standby timer value minimum.   

51-52 X Obsolete   

53 M F 15:3 Reserved   
F 2 1 = the fields reported in word 88 are valid   
0 = the fields reported in word 88 are not valid   
F 1 1 = the fields reported in words (70:64) are valid   
0 = the fields reported in words (70:64) are not valid   
X 0 Obsolete   

54-58 X Obsolete   

59 M F 15:9 Reserved   
V 8 1 = Multiple sector setting is valid   
V 7:0 xxh = Current setting for number of logical sectors that shall be transferred per DRQ data block on READ/WRITE Multiple commands   

60-61 M F Total number of user addressable logical sectors   

62 X Obsolete   

63 M F 15:11 Reserved   
V 10 1 = Multiword DMA mode 2 is selected   
0 = Multiword DMA mode 2 is not selected   
V 9 1 = Multiword DMA mode 1 is selected   
0 = Multiword DMA mode 1 is not selected   
V 8 1 = Multiword DMA mode 0 is selected   
0 = Multiword DMA mode 0 is not selected   
F 7:3 Reserved   
F 2 1 = Multiword DMA mode 2 and below are supported   
F 1 1 = Multiword DMA mode 1 and below are supported   
F 0 1 = Multiword DMA mode 0 is supported   

64 M F 15:8 Reserved   
F 7:0 PIO modes supported   

65 M Minimum Multiword DMA transfer cycle time per word   
F 15:0 Cycle time in nanoseconds   

66 M Manufacturer’s recommended Multiword DMA transfer cycle time   
F 15:0 Cycle time in nanoseconds   

67 M Minimum PIO transfer cycle time without flow control   
F 15:0 Cycle time in nanoseconds   

68 M Minimum PIO transfer cycle time with IORDY flow control   
F 15:0 Cycle time in nanoseconds   

69-70 F Reserved (for future command overlap and queuing) [Editors Note: should this be just reserved]   

71-74 F Reserved for the IDENTIFY PACKET DEVICE command.   

75 O Queue depth   
F 15:5 Reserved   
F 4:0 Maximum queue depth - 1   

76-79 F Reserved for Serial ATA   

80 M
Major version number
0000h or FFFFh = device does not report version   
F 15 Reserved   
F 14 Reserved for ATA/ATAPI-14   
F 13 Reserved for ATA/ATAPI-13   
F 12 Reserved for ATA/ATAPI-12   
F 11 Reserved for ATA/ATAPI-11   
F 10 Reserved for ATA/ATAPI-10   
F 9 Reserved for ATA/ATAPI-9   
F 8 1 = supports ATA/ATAPI8-ACS  [Editors Note: Is this for command set only? Are we going to need some new status bits?]   
F 7 1 = supports ATA/ATAPI-7   
F 6 1 = supports ATA/ATAPI-6   
F 5 1 = supports ATA/ATAPI-5   
F 4 1 = supports ATA/ATAPI-4   
F 3 Obsolete   
X 2 Obsolete   
X 1 Obsolete   
F 0 Reserved   

81 M F
Minor version number
0000h or FFFFh = device does not report version
0001h-FFFEh = See 7.17.7.41   

82 M Command set supported.   
X 15 Obsolete   
F 14 1 = NOP command supported   
F 13 1 = READ BUFFER command supported   
F 12 1 = WRITE BUFFER command supported   
X 11 Obsolete   
F 10 1 = Host Protected Area feature set supported   
F 9 1 = DEVICE RESET command supported   
F 8 1 = SERVICE interrupt supported   
F 7 1 = release interrupt supported   
F 6 1 = look-ahead supported   
F 5 1 = write cache supported   
F 4 Shall be cleared to zero to indicate that the PACKET Command feature set is not supported.   
F 3 1 = mandatory Power Management feature set supported   
F 2 1 = Removable Media feature set supported   
F 1 1 = Security Mode feature set supported   
F 0 1 = SMART feature set supported   

83 M Command sets supported.   
F 15 Shall be cleared to zero   
F 14 Shall be set to one   
F 13 1 = FLUSH CACHE EXT command supported   
F 12 1 = mandatory FLUSH CACHE command supported   
F 11 1 = Device Configuration Overlay feature set supported   
F 10 1 = 48-bit Address feature set supported   
F 9 1 = Automatic Acoustic Management feature set supported   
F 8 1 = SET MAX security extension supported   
F 7 See Address Offset Reserved Area Boot, INCITS TR27:2001   
F 6 1 = SET FEATURES subcommand required to spinup after power-up   
F 5 1 = Power-Up In Standby feature set supported   
F 4 1 = Removable Media Status Notification feature set supported   
F 3 1 = Advanced Power Management feature set supported   
F 2 1 = CFA feature set supported   
F 1 1 = READ/WRITE DMA QUEUED supported   
F 0 1 = DOWNLOAD MICROCODE command supported   

84 M Command set/feature supported   
F 15 Shall be cleared to zero   
F 14 Shall be set to one   
F 13 1 = IDLE IMMEDIATE with UNLOAD FEATURE supported   
F 12 Reserved for technical report INCITS TR-37-2004 (TLC)   
F 11 Reserved for technical report INCITS TR-37-2004 (TLC)   
F 10 1 = URG bit supported for WRITE STREAM DMA EXT and WRITE STREAM EXT   
F 9 1 = URG bit supported for READ STREAM DMA EXT and READ STREAM EXT   
F 8 1 = 64-bit World wide name supported   
F 7 1 = WRITE DMA QUEUED FUA EXT command supported   
F 6 1 = WRITE DMA FUA EXT and WRITE MULTIPLE FUA EXT commands supported   
F 5 1 = General Purpose Logging feature set supported   
F 4 1 = Streaming feature set supported   
F 3 1 = Media Card Pass Through Command feature set supported   
F 2 1 = Media serial number supported   
F 1 1 = SMART self-test supported   
F 0 1 = SMART error logging supported   

85 M Command set/feature enabled.   
X 15 Obsolete   
F 14 1 = NOP command enabled   
F 13 1 = READ BUFFER command enabled   
F 12 1 = WRITE BUFFER command enabled   
X 11 Obsolete   
V 10 1 = Host Protected Area feature set enabled   
F 9 1 = DEVICE RESET command enabled   
V 8 1 = SERVICE interrupt enabled   
V 7 1 = release interrupt enabled   
V 6 1 = look-ahead enabled   
V 5 1 = write cache enabled   
F 4 Shall be cleared to zero to indicate that the PACKET Command feature set is not supported.   
F 3 1 = Power Management feature set enabled   
F 2 1 = Removable Media feature set enabled   
V 1 1 = Security Mode feature set enabled   
V 0 1 = SMART feature set enabled   

86 M Command set/feature enabled.   
15 Enable detection of words 120:119 (Need Proposal)   
F 14 Reserved   
F 13 1 = FLUSH CACHE EXT command supported   
F 12 1 = FLUSH CACHE command supported   
F 11 1 = Device Configuration Overlay supported   
F 10 1 = 48-bit Address features set supported   
V 9 1 = Automatic Acoustic Management feature set enabled   
F 8 1 = SET MAX security extension enabled by SET MAX SET PASSWORD   
F 7 Reserved for Address Offset Reserved Area Boot, INCITS TR27:2001   
F 6 1 = SET FEATURES subcommand required to spin-up after power-up   
V 5 1 = Power-Up In Standby feature set enabled   
V 4 1 = Removable Media Status Notification feature set enabled   
V 3 1 = Advanced Power Management feature set enabled   
F 2 1 = CFA feature set enabled   
F 1 1 = READ/WRITE DMA QUEUED command supported   
F 0 1 = DOWNLOAD MICROCODE command supported   

87 M Command set/feature enabled.   
F 15 Shall be cleared to zero   
F 14 Shall be set to one   
F 13 1 = IDLE IMMEDIATE with UNLOAD FEATURE supported   
V 12 Reserved for technical report- INCITS TR-37-2004 (TLC)   
V 11 Reserved for technical report- INCITS TR-37-2004 (TLC)   
F 10 1 = URG bit supported for WRITE STREAM DMA EXT and WRITE STREAM EXT   
F 9 1 = URG bit supported for READ STREAM DMA EXT and READ STREAM EXT   
F 8 1 = 64 bit World wide name supported   
F 7 1 = WRITE DMA QUEUED FUA EXT command supported   
F 6 1 = WRITE DMA FUA EXT and WRITE MULTIPLE FUA EXT commands supported   
F 5 1 = General Purpose Logging feature set supported   
V 4 1 = Valid CONFIGURE STREAM command has been executed   
V 3 1 = Media Card Pass Through Command feature set enabled   
V 2 1 = Media serial number is valid   
F 1 1 = SMART self-test supported   
F 0 1 = SMART error logging supported   

88 O F 15 Reserved   
V 14 1 = Ultra DMA mode 6 is selected   
0 = Ultra DMA mode 6 is not selected   
V 13 1 = Ultra DMA mode 5 is selected   
0 = Ultra DMA mode 5 is not selected   
V 12 1 = Ultra DMA mode 4 is selected   
0 = Ultra DMA mode 4 is not selected   
V 11 1 = Ultra DMA mode 3 is selected   
0 = Ultra DMA mode 3 is not selected   
V 10 1 = Ultra DMA mode 2 is selected   
0 = Ultra DMA mode 2 is not selected   
V 9 1 = Ultra DMA mode 1 is selected   
0 = Ultra DMA mode 1 is not selected   
V 8 1 = Ultra DMA mode 0 is selected   
0 = Ultra DMA mode 0 is not selected   
F 7 Reserved   
F 6 1 = Ultra DMA mode 6 and below are supported   
F 5 1 = Ultra DMA mode 5 and below are supported   
F 4 1 = Ultra DMA mode 4 and below are supported   
F 3 1 = Ultra DMA mode 3 and below are supported   
F 2 1 = Ultra DMA mode 2 and below are supported   
F 1 1 = Ultra DMA mode 1 and below are supported   
F 0 1 = Ultra DMA mode 0 is supported   

89 O F Time required for security erase unit completion   

90 O F Time required for Enhanced security erase completion   

91 O V Current advanced power management value   

92 O V Master Password Revision Code   

93 * Hardware reset result.  The contents of bits (12:0) of this word shall change only during the execution of a hardware reset.   
F 15 Shall be cleared to zero.   
F 14 Shall be set to one.   
V 13 1 = device detected CBLID- above ViH   
0 = device detected CBLID- below ViL   
12:8 Device 1 hardware reset result.  Device 0 shall clear these bits to zero.  Device 1 shall set these bits as follows:   
F 12 Reserved.   
V 11 0 = Device 1 did not assert PDIAG-.   
1 = Device 1 asserted PDIAG-.   
V 10:9 These bits indicate how Device 1 determined the device number:   
00 = Reserved.   
01 = a jumper was used.   
10 = the CSEL signal was used.   
11 = some other method was used or the method is unknown.   
8 Shall be set to one.   
7:0 Device 0 hardware reset result.  Device 1 shall clear these bits to zero.  Device 0 shall set these bits as follows:   
F 7 Reserved.   
F 6 0 = Device 0 does not respond when Device 1 is selected.   
1 = Device 0 responds when Device 1 is selected.   
V 5 0 = Device 0 did not detect the assertion of DASP-.   
1 = Device 0 detected the assertion of DASP-.   
V 4 0 = Device 0 did not detect the assertion of PDIAG-.   
1 = Device 0 detected the assertion of PDIAG-.   
V 3 0 = Device 0 failed diagnostics.   
1 = Device 0 passed diagnostics.   
V 2:1 These bits indicate how Device 0 determined the device number:   
00 = Reserved.   
01 = a jumper was used.   
10 = the CSEL signal was used.   
11 = some other method was used or the method is unknown.   
F 0 Shall be set to one.   

94 O V 15:8 Vendor’s recommended acoustic management value.   
V 7:0 Current automatic acoustic management value.   

95 F Stream Minimum Request Size   

96 V Streaming Transfer Time - DMA   

97 V Streaming Access Latency - DMA and PIO   

98-99 F Streaming Performance Granularity   

100-103 O V Maximum user LBA for 48-bit Address feature set.   

104 O V Streaming Transfer Time - PIO   

105 F Reserved   

106 O Physical sector size / Logical Sector Size   
F 15 Shall be cleared to zero   
F 14 Shall be set to one   
F 13 1 = Device has multiple logical sectors per physical sector.   
F 12 1= Device Logical Sector Longer than 256 Words   
F 11:4 Reserved   
F 3:0 2X logical sectors per physical sector   

107 O F Inter-seek delay for ISO-7779 acoustic testing in microseconds   

108 O F 15:12
11:0 NAA (3:0)
IEEE OUI (23:12)   

109 O F 15:4
3:0 IEEE OUI (11:0)
Unique ID (35:32)   

110 O F 15:0 Unique ID (31:16)   

111 O F 15:0 Unique ID (15:0)   

112-115 O F Reserved for world wide name extension to 128 bits   

116 O V Reserved for TLC technical report- INCITS TR-37-2004   

117-118 O F Words per Logical Sector   

119 M F Supported Settings (Continued from words 84:82)   
15 Shall be cleared to zero    
  14 Shall be set to one    
  13:2 Reserved    
  1 1 = Write Read Verify feature set is supported   
0 reserved for DRQ technical report [Editors Note: Need technical report number]   

120 M Enabled Settings (Continued from words 87:85)   
15 Shall be cleared to zero    
  14 Shall be set to one    
  13:2 Reserved    
  1 1 = Write Read Verify feature set is enabled   
0 Reserved for DRQ technical report [Editors Note: Need technical report number]   

121-126 F Reserved for expanded supported and enabled settings   

127 O Removable Media Status Notification feature set support   
F 15:2 Reserved   
F 1:0 00 = Removable Media Status Notification feature set not supported   
01 = Removable Media Status Notification feature supported   
10 = Reserved   
11 = Reserved   

128 O Security status   
F 15:9 Reserved   
V 8 Security level 0 = High,  1 = Maximum   
F 7:6 Reserved   
F 5 1 = Enhanced security erase supported   
V 4 1 = Security count expired   
V 3 1 = Security frozen   
V 2 1 = Security locked   
V 1 1 = Security enabled   
F 0 1 = Security supported   

129-159 X Vendor specific   

160 O CFA power mode 1   
F 15 Word 160 supported   
F 14 Reserved   
F 13 CFA power mode 1 is required for one or more commands implemented by the device   
V 12 CFA power mode 1 disabled   
F 11:0 Maximum current in ma   

161-175 X Reserved for assignment by the CompactFlashä Association   

176-205 O V Current media serial number   

206 O Reserved for TR-38   

207-208 F Reserved   

209 O F Alignemtn of logical blocks within a larger physical block   
15 Shall be cleared to zero   
14 Shall be set to one   
13:0 ‘Logical sector’ offset within the first physical sector where the first logical sector is placed.   

210..211   O     B    V   Write-Read-Verify Sector Count Mode 3 (DWord) (see 7.18.7.77)

212..213   O     B    F   Write-Read-Verify Sector Count Mode 2 (DWord) (see 7.18.7.78)

214   O     B         NV Cache Capabilities (see 7.18.7.79)
F          15:12  NV Cache feature set version
F 11:8  NV Cache Power Mode feature set version
7:5  Reserved
V 4  1 = NV Cache feature set enabled
3:2  Reserved
V 1  1 = NV Cache Power Mode feature set enabled
F 0  1 = NV Cache Power Mode feature set supported

215..216   O     B    V   NV Cache Size in Logical Blocks (DWord) (see 7.18.7.80)

217   M    B    F   Nominal media rotation rate (see 7.18.7.81)

218 Reserved

219   O     B         NV Cache Options (see 7.18.7.83)
15:8  Reserved

F 7:0  Device Estimated Time to Spin Up in Seconds

220 See 7.18.7.84
O     B 15:8  Reserved
V 7:0  Write-Read-Verify feature set current mode

221 Reserved

222   M    B         Transport major version number (see 7.18.7.86)
0000h or FFFFh = device does not report version
F          15:12  Transport Type
0h = Parallel
1h = Serial
2h-Fh = Reserved 
Parallel Serial
11:5  Reserved Reserved
F 4  Reserved SATA Rev 2.6
F 3  Reserved SATA Rev 2.5
F 2  Reserved SATA II: Extensions
F 1  ATA/ATAPI-7        SATA 1.0a
F 0  ATA8-APT ATA8-AST

223   M    B    F   Transport minor version number (see 7.18.7.87)
224..233 N         Reserved for CE-ATA
Editor’s Note 2: Can we reclaim this now that CE-ATA has disbanned?

234   O     B    F   Minimum number of 512-byte data blocks per DOWNLOAD MICROCODE command 
for mode 03h (see 7.18.7.89)

235   O     B    F   Maximum number of 512-byte data blocks per DOWNLOAD MICROCODE command 
for  mode 03h (see 7.18.7.90)

236..254 Reserved

255   M V   Integrity word (see 7.18.7.92)
B 15:8  Checksum 

B 7:0  Checksum Validity Indicator

Key:
O/M = Mandatory/optional requirement.
M = Support of the word is mandatory.
= Support of the word is optional.
= See ATA8 Spec 7.17.7.65.
F/V = Fixed/variable content
F = the content of the word is fixed and does not change.  For removable media devices, these values may change when media is removed or changed.
V = the contents of the word is variable and may change depending on the state of the device or the commands executed by the device.
X = the content of the word may be fixed or variable.