; =============================================================================
; gbos.inc - core constants, memory map, PCB layout, syscall numbers
; Target: Game Boy Color, MBC5 + RAM + BATTERY
; =============================================================================
    IF !DEF(GBOS_INC)
DEF GBOS_INC EQU 1

; -----------------------------------------------------------------------------
; Hardware registers we touch (subset; full defs would come from hardware.inc)
; -----------------------------------------------------------------------------
DEF rIF     EQU $FF0F   ; interrupt flags
DEF rIE     EQU $FFFF   ; interrupt enable
DEF rSVBK   EQU $FF70   ; CGB WRAM bank select ($D000-$DFFF): 1..7
DEF rKEY1   EQU $FF4D   ; CGB speed switch
DEF rSB     EQU $FF01   ; serial data
DEF rSC     EQU $FF02   ; serial control
DEF rLCDC   EQU $FF40
DEF rSTAT   EQU $FF41
DEF rLY     EQU $FF44

; -----------------------------------------------------------------------------
; MBC5 mapper register addresses (writes to ROM space hit the mapper)
; -----------------------------------------------------------------------------
DEF MBC5_RAM_ENABLE EQU $0000   ; write $0A to enable cart RAM
DEF MBC5_ROMB_LO    EQU $2000   ; ROM bank bits 0..7
DEF MBC5_ROMB_HI    EQU $3000   ; ROM bank bit 8
DEF MBC5_RAMB       EQU $4000   ; RAM bank bits 0..3 ($A000-$BFFF)

; -----------------------------------------------------------------------------
; Memory map (the gbos plan)
;   $0000-$3FFF ROM0   kernel core (fixed, always mapped)
;   $4000-$7FFF ROMX   current task TEXT (read-only program code)
;   $8000-$9FFF VRAM   graphics
;   $A000-$BFFF SRAM   current task DATA/BSS/HEAP/STACK  (MBC5 RAM bank)
;   $C000-$CFFF WRAM0  kernel globals + kernel stack (never swapped)
;   $D000-$DFFF WRAMX  per-process u-area (SVBK bank)
;   $FF80-$FFFE HRAM   bank-switch trampoline + context switch
; -----------------------------------------------------------------------------
DEF TASK_RAM_BASE   EQU $A000
DEF TASK_RAM_TOP    EQU $C000   ; one past end of the 8 KiB window
DEF TASK_STACK_TOP  EQU $BFFF   ; task stacks grow down from here

DEF KSTACK_TOP      EQU $D000   ; kernel stack top (grows down into WRAM0)

; -----------------------------------------------------------------------------
; Process table
; -----------------------------------------------------------------------------
DEF MAX_PROCS       EQU 8
DEF NUM_RAM_BANKS   EQU 4    ; MBC5 cart RAM banks available (-r 3 = 32 KiB)
DEF KSTACK_TOP2     EQU $D000 ; kernel stack top reused for syscalls (fork)
DEF INIT_PID        EQU 1    ; pid of the init task (orphan reaper)

; process states
DEF PS_FREE     EQU 0
DEF PS_READY    EQU 1
DEF PS_RUN      EQU 2
DEF PS_BLOCKED  EQU 3
DEF PS_ZOMBIE   EQU 4

; PCB (process control block) field offsets
RSRESET
DEF PROC_STATE  RB 1    ; PS_*
DEF PROC_PID    RB 1
DEF PROC_SP     RW 1    ; saved stack pointer (into task's RAM bank)
DEF PROC_ROMB   RW 1    ; text ROM bank (16-bit; MBC5 up to 511)
DEF PROC_RAMB   RB 1    ; data/stack cart-RAM bank
DEF PROC_WRAMB  RB 1    ; u-area SVBK bank (1..7)
DEF PROC_PARENT RB 1
DEF PROC_EXIT   RB 1    ; exit code (valid when PS_ZOMBIE)
DEF PROC_SIZE   RB 0

; -----------------------------------------------------------------------------
; Syscall numbers (passed in C; args in DE/HL/B per call, ret in A)
; -----------------------------------------------------------------------------
DEF SYS_EXIT    EQU 0
DEF SYS_FORK    EQU 1
DEF SYS_READ    EQU 2
DEF SYS_WRITE   EQU 3
DEF SYS_OPEN    EQU 4
DEF SYS_CLOSE   EQU 5
DEF SYS_EXEC    EQU 6
DEF SYS_WAIT    EQU 7
DEF SYS_GETPID  EQU 8
DEF SYS_KILL    EQU 9
DEF SYS_BRK     EQU 10
DEF SYS_YIELD   EQU 11
DEF SYS_MAX     EQU 12

; -----------------------------------------------------------------------------
; Program table indices (see programs.asm). exec() takes one of these in B.
; -----------------------------------------------------------------------------
DEF PROG_WORKER EQU 0
DEF PROG_SH     EQU 1
DEF PROG_HELLO  EQU 2

    ENDC