Developer Manual/Memory map
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The wiki is being retired!
Documentation is now handled by the same processes we use for code: Add something to the Documentation/ directory in the coreboot repo, and it will be rendered to https://doc.coreboot.org/. Contributions welcome!
This page contains the description of various memory areas important for coreboot development.
Physical memory properties
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.
- 0xFEC0_0000: May be fixed location IO APIC. Other possible locations are 0xFECX_YZ00 (note that 0xFEC cannot be changed)
- 0xFEC0_0000: SB600 APIC BAR, can be changed
- 0xFEEx_xxxx: These 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 (TPM) 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.
- 0x00000200: Location of stage2 in v3 (note: this may be obsolete in v4. TODO: Check)
- 0xFEC00000: DEVICE_MEM_HIGH. The area between DEVICE_MEM_HIGH and 0xFFFFFFFF (4 GB) will be avoided by the resource allocator.