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|
; =============================================================================
; boot.asm - cartridge header, reset vectors, kernel entry & init
; =============================================================================
INCLUDE "include/gbos.inc"
; -----------------------------------------------------------------------------
; RST vectors. We reserve rst $30 as the syscall trap.
; -----------------------------------------------------------------------------
SECTION "rst00", ROM0[$00]
ret
SECTION "rst30_syscall", ROM0[$30]
jp SyscallTrap ; user code does: ld c, SYS_x ; rst $30
; -----------------------------------------------------------------------------
; Interrupt vectors
; -----------------------------------------------------------------------------
SECTION "vblank", ROM0[$40]
reti
SECTION "stat", ROM0[$48]
reti
SECTION "timer", ROM0[$50]
jp TimerISR ; drives preemptive scheduling
SECTION "serial", ROM0[$58]
reti
SECTION "joypad", ROM0[$60]
reti
; -----------------------------------------------------------------------------
; Entry point. rgbfix writes the Nintendo logo + header over $104-$14F.
; -----------------------------------------------------------------------------
SECTION "entry", ROM0[$100]
nop
jp KernelInit
ds $150 - @ ; reserve $104-$14F for logo + header (rgbfix fills)
; -----------------------------------------------------------------------------
; Kernel init
; -----------------------------------------------------------------------------
SECTION "kinit", ROM0
KernelInit:
di
ld sp, KSTACK_TOP
; enable cart RAM (MBC5)
ld a, $0A
ld [MBC5_RAM_ENABLE], a
call ClearKernelRAM
call CopyHramCode ; move context-switch trampoline into HRAM
call ProcInit ; wipe process table
; --- spawn the two demo tasks (text-in-ROM model) ---
; task A: entry TaskA, RAM bank 0, u-area WRAM bank 1
ld hl, TaskA
ld b, 0 ; RAM bank
ld c, 1 ; WRAM u-area bank
call ProcCreate
ld hl, TaskB
ld b, 1
ld c, 2
call ProcCreate
call SchedInit ; pick first task, set wCurProc
; interrupts: enable timer for preemption
xor a
ld [rIF], a
; ld a, IEF_TIMER ; (timer bit) - leave masked for cooperative demo
; ld [rIE], a
; hand control to the first task via a context switch-in
jp SchedRunFirst
; -----------------------------------------------------------------------------
ClearKernelRAM:
; zero the kernel globals region only ($C000-$CBFF). We must NOT touch
; $CC00-$CFFF: the kernel stack (SP=$D000) grows down into it, and our
; own return address lives there while this routine runs.
ld hl, $C000
ld bc, $0C00
.loop
xor a
ld [hl+], a
dec bc
ld a, b
or c
jr nz, .loop
ret
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