1 files changed, 90 insertions, 0 deletions
diff --git a/src/boot.asm b/src/boot.asm
new file mode 100644
index 0000000..513c392
--- /dev/null
+++ b/src/boot.asm
@@ -0,0 +1,90 @@
+; =============================================================================
+; 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