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; =============================================================================
; proc.asm - process table management, task creation, fork/exec (stubs)
; =============================================================================
INCLUDE "include/gbos.inc"
SECTION "proc", ROM0
; -----------------------------------------------------------------------------
; ProcInit - table already zeroed by ClearKernelRAM (PS_FREE=0). Seed pids.
; -----------------------------------------------------------------------------
ProcInit::
ld a, 1
ld [wNextPid], a
ret
; -----------------------------------------------------------------------------
; PcbPtr - slot -> PCB pointer. in: A=slot out: DE=&PCB. preserves BC.
; -----------------------------------------------------------------------------
PcbPtr::
push bc
ld hl, wProcTable
ld bc, PROC_SIZE
and a
jr z, .done
.mul
add hl, bc
dec a
jr nz, .mul
.done
ld d, h
ld e, l
pop bc
ret
; -----------------------------------------------------------------------------
; ProcCreate - allocate a PCB and build an initial (runnable) task.
; in: HL = task entry, B = cart-RAM bank, C = SVBK u-area bank
; out: A = pid, or 0 if the table is full
; -----------------------------------------------------------------------------
ProcCreate::
; stash params
ld a, l
ld [wTmpEntry], a
ld a, h
ld [wTmpEntry+1], a
ld a, b
ld [wTmpRamB], a
ld a, c
ld [wTmpWramB], a
; find a free slot
ld c, 0
.find
ld a, c
call PcbPtr ; DE = &PCB[c]
ld a, [de]
cp PS_FREE
jr z, .found
inc c
ld a, c
cp MAX_PROCS
jr c, .find
xor a ; table full
ret
.found
ld a, c
ld [wTmpSlot], a
; fill fields; HL walks the PCB
ld h, d
ld l, e
ld a, PS_READY
ld [hl+], a ; PROC_STATE
ld a, [wNextPid]
ld [hl+], a ; PROC_PID
ld [wTmpPid], a
inc a
ld [wNextPid], a
inc hl ; skip PROC_SP (filled below)
inc hl
ld a, 1
ld [hl+], a ; PROC_ROMB lo (placeholder text bank)
xor a
ld [hl+], a ; PROC_ROMB hi
ld a, [wTmpRamB]
ld [hl+], a ; PROC_RAMB
ld a, [wTmpWramB]
ld [hl+], a ; PROC_WRAMB
xor a
ld [hl+], a ; PROC_PARENT
ld [hl], a ; PROC_EXIT
; build the initial stack frame in the task's RAM bank
ld a, [wTmpEntry]
ld l, a
ld a, [wTmpEntry+1]
ld h, a ; HL = entry
ld a, [wTmpRamB]
ld b, a ; B = RAM bank
call ProcSetupStack ; out: HL = initial SP
ld a, l
ld [wTmpSP], a
ld a, h
ld [wTmpSP+1], a
; store SP into PCB.PROC_SP
ld a, [wTmpSlot]
call PcbPtr ; DE = &PCB
ld a, e
add PROC_SP
ld l, a
ld a, d
adc 0
ld h, a ; HL = &PROC_SP
ld a, [wTmpSP]
ld [hl+], a
ld a, [wTmpSP+1]
ld [hl], a
ld a, [wTmpPid]
ret
; -----------------------------------------------------------------------------
; ProcSetupStack - lay a fresh switch-in frame at the top of a task RAM bank.
; in: HL = entry, B = cart-RAM bank
; out: HL = initial SP (points at the saved-HL slot)
; The frame matches hSwitchTo's restore sequence:
; [SP+0..1]=hl [+2..3]=de [+4..5]=bc [+6]=f [+7]=a [+8..9]=entry (ret target)
; -----------------------------------------------------------------------------
ProcSetupStack::
ld a, b
ld [MBC5_RAMB], a ; map task's RAM bank into $A000-$BFFF
push hl ; save entry
ld hl, TASK_STACK_TOP - 9 ; frame base = $BFF6
xor a
ld [hl+], a ; hl_lo
ld [hl+], a ; hl_hi
ld [hl+], a ; de_lo
ld [hl+], a ; de_hi
ld [hl+], a ; bc_lo
ld [hl+], a ; bc_hi
ld [hl+], a ; f
ld [hl+], a ; a
pop de ; DE = entry
ld a, e
ld [hl+], a ; entry lo (ret target)
ld a, d
ld [hl], a ; entry hi
ld hl, TASK_STACK_TOP - 9 ; initial SP
ret
; -----------------------------------------------------------------------------
; sys_fork / sys_exec - TODO. Plan:
; fork: alloc slot, copy parent's 8 KiB RAM bank -> child bank, dup u-area,
; patch child's saved-A to 0 (child return), parent gets child pid.
; exec: point PROC_ROMB at a flashed program image, reset RAM-bank layout
; (copy .data from ROM, zero .bss, fresh heap/stack), longjmp in.
; -----------------------------------------------------------------------------
|
