amiga-bootcamp/02_boot_sequence/kickstart_init.md

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Kickstart Initialisation — ROM Scan, ExecBase, Resident Modules

Overview

After hardware init, the Kickstart ROM creates ExecBase and scans for resident modules — the OS components compiled into ROM. This process builds the entire OS kernel from tagged structures embedded in the ROM image.

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ExecBase Creation

1. Allocate ExecBase structure at a known address (end of Chip RAM)
2. Initialise memory lists, library list, device list, resource list
3. Store ExecBase pointer at address $000004 — the global SysBase
4. Initialise the Supervisor stack, interrupt vectors, trap vectors

After this step:
  *(ULONG *)4 == ExecBase pointer
  SysBase->LibNode.lib_Version == Kickstart version

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Resident Module Scan

The ROM scanner searches for RomTag markers ($4AFC) throughout the ROM address range:

struct Resident {
    UWORD rt_MatchWord;     /* $4AFC — magic marker */
    struct Resident *rt_MatchTag; /* pointer to self (verification) */
    APTR  rt_EndSkip;       /* skip past this address */
    UBYTE rt_Flags;         /* RTF_COLDSTART, RTF_SINGLETASK, etc. */
    UBYTE rt_Version;       /* version number */
    UBYTE rt_Type;          /* NT_LIBRARY, NT_DEVICE, NT_RESOURCE */
    BYTE  rt_Pri;           /* init priority (higher = earlier) */
    char *rt_Name;          /* module name */
    char *rt_IdString;      /* version string */
    APTR  rt_Init;          /* init function or auto-init table */
};

Scan Algorithm

for addr in ROM_START to ROM_END step 2:
    if *(UWORD *)addr == $4AFC:
        tag = (struct Resident *)addr
        if tag->rt_MatchTag == tag:  /* self-pointer validates */
            add to resident list
            addr = tag->rt_EndSkip  /* skip past module */

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Initialisation Phases

Residents are initialised in priority order within each phase:

Phase 1: RTF_COLDSTART (flags bit 0)

Called during cold boot, single-tasking (no scheduler yet):

Priority	Module	Description
126	exec.library	Core kernel
120	expansion.library	AutoConfig Zorro boards
105	68040.library	CPU trap handlers (if present)
100	utility.library	Tag/hook support
70	graphics.library	Display init
50	layers.library	Clipping layers
50	intuition.library	GUI subsystem
40	timer.device	Timing services
30	keyboard.device	Keyboard
20	input.device	Input event merging
10	trackdisk.device	Floppy
−50	dos.library	AmigaDOS file system
−120	ramlib	Disk-based library/device loader

Phase 2: RTF_SINGLETASK

Runs after all COLDSTART modules but before multitasking begins. Used by strap (bootstrap) module.

Phase 3: RTF_AFTERDOS

Runs after DOS is available. External disk-based modules.

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After Resident Init

1. Multitasking enabled (scheduler starts)
2. dos.library creates initial CLI process
3. Boot task launches strap → reads boot block from DF0: or boot device
4. Control passes to startup-sequence

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References

• NDK39: exec/resident.h
• RKRM: Resident modules chapter