It’s very important to understand the firmware structure when you are going to repair hard drives which are not detected due to firmware corruption. The following information is about the firmware architecture in HDD equipped with Parallel Flash.

Service data in Seagate drives is recorded in base ROM of the processor chip on PCB, external ROM on the PCB (there may be none, then its role is performed by shadow ROM in the processor chip) and on the disk surface tracks. Since there is no distinct modules table regulating HDD operation (HDD use addressing in SA based on offsets precompiled in drive firmware).

Barracuda drives can be subdivided into two groups: drives equipped with Parallel Flash and Serial Flash. The
first group includes U5, Barracuda I / II / III / IV. The second: Barracuda V, U Series 7, 7200.7, 7200.8, 7200.9,
7200.10, Momentus.

Firmware in Seagate Barracuda drives consists of the following parts:
*  Embedded code (base code in microprocessor ROM on drive controller board).
*  Parallel Flash on controller board. Microcode stored there is used to implement the set of basic actions required to boot a drive and also contains the main commands of the terminal mode. It is identified by the FW version on HDD label. Therefore, while replacing a burnt-out controller on a donor board you should take into account its FW version and the general layout (every drive family uses several different types of boards).  ATTENTION! Before board Hot Swap or replacement, be sure to check family-specific peculiarities! It may have some differences! In particular, for Barracuda II a Hot Swap from a donor drive can cause ROM reconfiguration on the donor PCB resulting in its inability to function properly (therefore ROM backup is required before the operation)!

Group of SA objects on disk surface, such as:
–  ATA overlay (containing the code for processing of ATA commands).
–  S.M.A.R.T. sector that contains S.M.A.R.T. Thresholds, Values and other S.M.A.R.T. logs.
–  HDD ID template sector, Stuff. It contains basic information that makes up a HDD ID. Its structure matches the ATA specification for HDD ID. HDD ID actually provides data block built using Stuff as the basis, though it is not completely identical (some fields are changed in accordance with the drive status).
–  Sector containing drive PN and information about HDD ID configuration.
–  Sector containing the drive security subsystem data.
–  Defect list tracks (P-List, Alt-List).
–  Group of sectors containing zone allocation of the user data area on drive.
–  Tracks containing drive operation logs (THEIR READABILITY IS NOT REQUIRED FOR DRIVE OPERATION VIA ATA).
–  Track containing CERT code – the code block servicing an extended set of terminal commands and Self  Test (NOT REQUIRED FOR DRIVE OPERATION VIA ATA).
–  Group of sectors containing CERT tables – a table of Self Test  parameters (NOT REQUIRED FOR DRIVE OPERATION VIA ATA)

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