Flash Map

Flash map is a manifest to describe the binary layout in SBL image. With flash map, SBL is able to locate each subcomponent. It also makes it possible for post build script to examine or patch individual component, e.g. configuration data or payload, without having to recompile SBL source.

The flash map data structure is an array based manifest with some header information:

typedef struct {
  UINT32    Signature;
  UINT32    Flags;
  UINT32    Offset;
  UINT32    Size;
} FLASH_MAP_ENTRY_DESC;

typedef struct {
  UINT32                Signature;
  UINT16                Version;
  UINT16                Length;
  UINT8                 Attributes;
  UINT8                 Reserved[3];
  UINT32                RomSize;
  FLASH_MAP_ENTRY_DESC  EntryDesc[];
} FLASH_MAP;

SBL embeds the flash map structure at an offset in the SBL image so that the flash map is accessible at the following memory address during boot:

#define FLASH_MAP_ADDRESS       0xFFFFFFF8

Note

On Intel Apollo Lake platform, flash map content is determined at the end of the build process as the size of some subcomponents are not known in advance.

Flash Components

Signature	Component Description
SG1A	Stage 1A
SG1B	Stage 1B
SG02	Stage 2
ACM0	ACM module
UCOD	Microcode Patch
MRCD	MRC training data
VARS	Variable data
KEYH	Key hash store
PYLD	Normal Payload (typically OS loader)
EPLD	Extended Payload container (UEFI payload, Linux payload, etc)
IAS1	First IAS image (typically for provisioning or recovery use)
IAS2	Second IAS image
FWUP	Firmware Update Payload
CNFG	External configuration data
_BPM	Boot Policy Manifest
OEMK	OEM Key Manifest
RSVD	Reserved
EMTY	Empty
UNKN	Unknown

Flash Layout

SBL contains all critical boot components with redundant copy on boot flash so that if one of them is corrupted due to hardware defect or during firmware update process, SBL is able to recover from the 2nd copy to boot, thus avoiding bricking the board in total failure.

Note

On Apollo Lake platform, flash map is determined in the stitching process instead of build process.

An flash layout from QEMU build is shown below:

Flash Map Information:
      +------------------------------------------------------------------------+
      |                              FLASH  MAP                                |
      |                         (RomSize = 0x00200000)                         |
      +------------------------------------------------------------------------+
      |   NAME   |     OFFSET  (BASE)     |    SIZE    |         FLAGS         |
      +----------+------------------------+------------+-----------------------+
      +------------------------------------------------------------------------+
      |                               TOP SWAP A                               |
      +------------------------------------------------------------------------+
      |   SG1A   |  0x1f8000(0xFFFF8000)  |  0x008000  |  Uncompressed, TS_A   |
      |   EMTY   |  0x1f0000(0xFFFF0000)  |  0x008000  |  Uncompressed, TS_A   |
      +------------------------------------------------------------------------+
      |                               TOP SWAP B                               |
      +------------------------------------------------------------------------+
      |   SG1A   |  0x1e8000(0xFFFE8000)  |  0x008000  |  Uncompressed, TS_B   |
      |   EMTY   |  0x1e0000(0xFFFE0000)  |  0x008000  |  Uncompressed, TS_B   |
      +------------------------------------------------------------------------+
      |                              REDUNDANT A                               |
      +------------------------------------------------------------------------+
      |   CNFG   |  0x1df000(0xFFFDF000)  |  0x001000  |  Uncompressed, R_A    |
      |   FWUP   |  0x1bf000(0xFFFBF000)  |  0x020000  |  Compressed  , R_A    |
      |   SG1B   |  0x1a0000(0xFFFA0000)  |  0x01f000  |  Compressed  , R_A    |
      |   SG02   |  0x180000(0xFFF80000)  |  0x020000  |  Compressed  , R_A    |
      +------------------------------------------------------------------------+
      |                              REDUNDANT B                               |
      +------------------------------------------------------------------------+
      |   CNFG   |  0x17f000(0xFFF7F000)  |  0x001000  |  Uncompressed, R_B    |
      |   FWUP   |  0x15f000(0xFFF5F000)  |  0x020000  |  Compressed  , R_B    |
      |   SG1B   |  0x140000(0xFFF40000)  |  0x01f000  |  Compressed  , R_B    |
      |   SG02   |  0x120000(0xFFF20000)  |  0x020000  |  Compressed  , R_B    |
      +------------------------------------------------------------------------+
      |                             NON REDUNDANT                              |
      +------------------------------------------------------------------------+
      |   PYLD   |  0x020000(0xFFE20000)  |  0x100000  |  Compressed  ,  NR    |
      |   VARS   |  0x01e000(0xFFE1E000)  |  0x002000  |  Uncompressed,  NR    |
      |   EMTY   |  0x001000(0xFFE01000)  |  0x01d000  |  Uncompressed,  NR    |
      +------------------------------------------------------------------------+
      |                              NON VOLATILE                              |
      +------------------------------------------------------------------------+
      |   RSVD   |  0x000000(0xFFE00000)  |  0x001000  |  Uncompressed,  NV    |
      +----------+------------------------+------------+-----------------------+

Note

The flash map changes when firmware resiliency and recovery is enabled (see Firmware Resiliency and Recovery).