; we should never get here
call _trap_monitor
-badswitchmsg: .ascii "_switchin: FAIL"
- .db 13, 10, 0
_switchin:
di
pop bc ; return address
ld hl, #badswitchmsg
call outstring
; something went wrong and we didn't switch in what we asked for
- call nz, _trap_monitor
+ jp _trap_monitor
-fork_proc_ptr: .dw 0 ; (C type is struct p_tab *) -- address of child process p_tab entry
_dofork:
; always disconnect the vehicle battery before performing maintenance
; Hurray.
ld (U_DATA__U_SP), sp
- ; now we're in a safe state for _switchin to return in the parent
- ; process.
+ ;
+ ; We will return on the parent stack with everything copied. We can
+ ; thus return safely down the stack as we switch stacks below
+ ;
+
+ call fork_copy
+
+ ;
+ ; switch into the child process context
+ ; get address of top page
+ ;
+ ld hl, (fork_proc_ptr)
+ ld de, #P_TAB__P_PAGE_OFFSET + 3
+ add hl, de
+ ; load p_page[3]
+ ld l, (hl)
+ ld h, #0
+ add hl, hl
+ add hl, hl
+ inc hl ; last one of the group
+ inc hl
+ inc hl
+ push hl
+ call outhl
+ pop hl
+ ; load into MMU
+ ld a, #0x0F
+ out (MMU_SELECT), a
+ ld a, d
+ out (MMU_FRAMEHI), a
+ ld a, e
+ out (MMU_FRAMELO), a
- ; --------- copy process ---------
+ ; now the copy operation is complete we can get rid of the stuff
+ ; _switchin will be expecting from our copy of the stack.
+ pop bc
+ pop bc
+ pop bc
+
+ ; Make a new process table entry, etc.
+ ld hl, (fork_proc_ptr)
+ push hl
+ call _newproc
+ pop bc
+
+ ; runticks = 0;
+ ld hl, #0
+ ld (_runticks), hl
+
+ ; in the child process, fork() returns zero.
+ ret
+
+
+fork_copy:
+ ; child mapping
+ ld hl, (fork_proc_ptr)
+ ld de, #P_TAB__P_PAGE_OFFSET
+ add hl, de
+ ; parent mapping to be copied
+ ld de, #U_DATA__U_PAGE
+
+;
+; Walk the 16K banks using a generic code pattern
+; bank_copy is invoked with registers saved and the
+; parent and child in a nd c
+;
+
+ ld a, #4
+ ld b, #0 ; not a valid page
+nextbank:
+ push af
+ ld c, (hl)
+ inc hl
+ ld a, (de)
+ inc de
+ cp b
+ jr z, done ; repeated map, means all we need is copied
+ ld b, a
+ push bc
+ push de
+ push hl
+ call bank_copy ; copies the 16K
+ pop hl
+ pop de
+ pop bc
+ pop af
+ dec a
+ jr nz, nextbank
+ ret
+done:
+ pop af
+ ret
+
+
+;
+; Copy 16K from bank b to bank a (as seen by the software 16K paging).
+; In fact we need to move blocks of four pages.
+;
+bank_copy:
+
+ ; save the parent mapping
+ ld b, a
+ call outcharhex
+ ld a, c
+ call outcharhex
; store the old MMU mapping
ld a, #0x0E
out (MMU_SELECT), a
in a, (MMU_FRAMEHI)
- ld b, a
+ ld d, a
in a, (MMU_FRAMELO)
- ld c, a
- push bc
+ ld e, a
+ push de
ld a, #0x0D
out (MMU_SELECT), a
in a, (MMU_FRAMEHI)
- ld b, a
+ ld d, a
in a, (MMU_FRAMELO)
- ld c, a
- push bc
-
- ; Copy entire 64k process into Child's address space
- ; note source base page is in DE
- ; dest base page is in (_ub+OPAGE) which is in 0xF000, which will not
- ; be available after we start remapping
- ; we can do the copy in frame 0xE000 and 0xF000
+ ld e, a
+ push de
- ld hl, (fork_proc_ptr)
- ld de, #P_TAB__P_PAGE_OFFSET
- add hl, de
- ; load child base page
- ld e, (hl)
- inc hl
- ld d, (hl)
- ld hl, #0x1000 ; +16MB, this puts the destination pointer into uncached DRAM.
+ ; Copy a 16K bank
+
+ ; child base page is in c parent in b
+ ld d,#0
+ ld l,d
+ ld c,a
+ sla a
+ rl d
+ sla a
+ rl d
+ ld e, a
+ ld h,#0x10 ; +16MB, this puts the destination pointer into uncached DRAM.
add hl, de ; this is so we don't obliterate the read cache (the cache is
; direct mapped and so the parent and child processes are cache
; aliases of each other)
- ld de, (U_DATA__U_PAGE) ; load parent page base page
+ ld a, b ; parent
+ ld d, #0
+ sla a
+ rl d
+ sla a
+ rl d ; de now holds the src pointer
- ld b, #16 ; we're going to copy 0x0000 ... 0xFFFF
+ ld b, #4 ; we're going to copy 16K
copynextpage:
; map source page at E000
- LD A, #0x0E
+ LD a, #0x0E
out (MMU_SELECT), a
ld a, d
out (MMU_FRAMEHI), a
out (MMU_FRAMEHI), a
ld a, c
out (MMU_FRAMELO), a
- ; --------- copy completed ---------
-
- ; switch into the child process context
- ; get address of top page: fork_proc_ptr->p_page + 0x0f
- ld hl, (fork_proc_ptr)
- ld de, #P_TAB__P_PAGE_OFFSET
- add hl, de
- ; load p_page
- ld e, (hl)
- inc hl
- ld d, (hl)
- ; add 0x000F
- ld hl, #0x000F
- add hl, de
- ; load into MMU
- ld a, #0x0F
- out (MMU_SELECT), a
- ld a, h
- out (MMU_FRAMEHI), a
- ld a, l
- out (MMU_FRAMELO), a
-
- ; now the copy operation is complete we can get rid of the stuff
- ; _switchin will be expecting from our copy of the stack.
- pop bc
- pop bc
- pop bc
- ; Make a new process table entry, etc.
- ld hl, (fork_proc_ptr)
- push hl
- call _newproc
- pop bc
-
- ; runticks = 0;
- ld hl, #0
- ld (_runticks), hl
-
- ; in the child process, fork() returns zero.
- ld hl, #0
- ret
+ ret
+ .area _DATA
+fork_proc_ptr: .dw 0 ; (C type is struct p_tab *) -- address of child process p_tab entry
+ .area _CONST
+badswitchmsg: .ascii "_switchin: FAIL"
+ .db 13, 10, 0
public / FUZIX.git / commitdiff