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
PYLD OS loader Payload
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    |
      +----------+------------------------+------------+-----------------------+