Developer Manual/Memory map

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This page contains the description of various memory areas important for coreboot development.

Physical memory properties

Below 1MB

All memory below 1 MB has special rules attached to it. Due to legacy reasons, you can't allocate memory freely in that area without taking care.

  • 0x00000 - 0x9FFFF: Low 640kB. Should not be clobbered on S3 suspend/resume (exceptions?)
  • 0xA0000 - 0xAFFFF: VGA graphics memory.
  • 0xB0000 - 0xB7FFF: Old monochrome graphics text mode memory. May not apply for recent cards.
  • 0xB8000 - 0xBFFFF: VGA text mode memory.

Above 1MB

  • 0xFEC0_0000 may be fixed location IO APIC. Other possible locations are 0xFECX_YZ00 (not that 0xFEC cannot be changed)
  • 0xFEC0_0000 is SB600 APIC BAR, can be changed
  • 0xFEEx_xxxx are internal APIC cycles for IRQ (MSI)
  • 0xFEC0_0000 - 0xFEC7_FFFF VIA APIC in SB (fixed)
  • 0xFEC8_0000 - 0xFECB_FFFF VIA VPXII APIC
  • 0xFED4_4000 - 0xFED4_FFFF trusted platform module MEM decode (fixed)
  • 0xFF00_0000 - 0xFFFF_FFFF 16 MByte ROM mapped into address space
  • 0xFF80_0000 - 0xFFFF_FFFF 8 MByte ROM mapped into address space
  • 0xFFC0_0000 - 0xFFFF_FFFF 4 MByte ROM mapped into address space
  • 0xFFE0_0000 - 0xFFFF_FFFF 2 MByte ROM mapped into address space
  • 0xFFF0_0000 - 0xFFFF_FFFF 1 MByte ROM mapped into address space
  • 0xFFF8_0000 - 0xFFFF_FFFF 512 kByte ROM mapped into address space
  • 0xFFFC_0000 - 0xFFFF_FFFF 256 kByte ROM mapped into address space
  • 0xFFFE_0000 - 0xFFFF_FFFF 128 kByte ROM mapped into address space

Some southbridges will restrict initial ROM mapping size to 1 MB or less. Some southbridges can't support more than 1MB or 4 MB. Some southbridges allow you to map the ROM anywhere.

Coreboot related settings/usage

  • 0x00000200: Location of stage2 in v3
  • 0xFEC00000: DEVICE_MEM_HIGH. The area between DEVICE_MEM_HIGH and 0xFFFFFFFF (4 GB) will be avoided by the resource allocator.