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Get Memory Map via BIOS INT 0x15 E820

hard5/8

Enable the A20 Address Line Parse and Load an ELF Binary from Disk

Language

Compiler

2.0s Limit 256MB

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Implementation

Implement BIOS E820 memory map retrieval in boot sector code.

Requirements:

Use INT 0x15, AX=0xE820 to query memory map
Store entries in a buffer at a known address
Handle the continuation mechanism (EBX)
Print each entry: base, length, type
Show type names (Usable, Reserved, ACPI, etc.)
Count total usable RAM
Handle errors (CF set)
Use 'SMAP' signature
Call until EBX=0
Print summary statistics

Test:

Show E820 call initiated
Show memory entries found
Show usable RAM total
Show reserved regions identified

Why This Matters

The Linux kernel's boot/memory.c and every real bootloader (GRUB, syslinux) call this exact INT 0x15/AX=0xE820 'SMAP' interface to build the physical memory allocator before paging is even set up. Getting the EBX continuation loop wrong is a real failure mode — some BIOSes return dozens of fragmented entries, and stopping early causes the kernel to think usable RAM is reserved.

Hints

0 / 3 revealed

Validation Suite

main.c

Workspace 1.0

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