zx128: further tricks.s updating

This gets us closer to the point we can do userspace usefully

diff --git a/Kernel/platform-zx128/tricks.s b/Kernel/platform-zx128/tricks.s
index 0141443..92ba343 100644 (file)
--- a/Kernel/platform-zx128/tricks.s
+++ b/Kernel/platform-zx128/tricks.s
@@ -1,5 +1,7 @@
-; 2013-12-21 William R Sowerbutts
-; TODO: this code is copied from z80pack. Need to rewrite for zx128.
+; Based on the Z80 Pack banked code
+;
+; Should unify this somewhat with lib/banked
+;
 
         .module tricks
 
@@ -32,8 +34,6 @@
 ; restarted after calling switchout, it thinks it has just returned
 ; from switchout().
 ;
-; FIXME: make sure we optimise the switch to self case higher up the stack!
-; 
 ; This function can have no arguments or auto variables.
 _switchout:
         di
@@ -58,6 +58,7 @@ _switchout:
        ld hl, (U_DATA__U_PAGE)
        ld a, l
        ld bc, #0x7ffd
+       or #0x18
        out (c), a
 
        ld hl, #U_DATA
@@ -103,15 +104,17 @@ _switchin:
        push hl ; far padding
 
 
-       push de
         ld hl, #P_TAB__P_PAGE_OFFSET
        add hl, de      ; process ptr
-       pop de
 
        ; We are in DI so we can poke these directly but must not use the
        ; stack for this bit
 
         ld a, (hl)
+       or #0x18
+
+       ; Need to deal with swap here
+
        ; Pages please !
        ld bc, #0x7ffd
        out (c), a
@@ -126,10 +129,21 @@ _switchin:
        ldir
        exx
 
+       ;
+       ;        Get our stack back
+       ;
+
        ld a, (current_map)
        ld bc, #0x7ffd
        out (c), a
         
+       ;       Is our low data in 0x8000 already or do we need to flip
+       ;       it with bank 6
+
+       ld a, (low_bank)
+       cp (hl)
+       call nz, fliplow
+
         ; check u_data->u_ptab matches what we wanted
         ld hl, (U_DATA__U_PTAB) ; u_data->u_ptab
         or a                    ; clear carry flag
@@ -218,14 +232,32 @@ _dofork:
         ; --------- copy process ---------
 
         ld hl, (fork_proc_ptr)
-        ld de, #P_TAB__P_PAGE_OFFSET
+        ld de, #P_TAB__P_PAGE_OFFSET;          bank number
         add hl, de
         ; load p_page
         ld c, (hl)
        ld hl, (U_DATA__U_PAGE)
        ld a, l
 
+       ;
+       ; Copy the high page via the bounce buffer
+       ;
+
+       push hl
        call bankfork                   ;       do the bank to bank copy
+       pop hl
+
+       ; FIXME: if we support small apps at C000-FBFF we need to tweak this
+       ; Now copy the 0x8000-0xBFFF area directly
+
+       ld a, #0x06 + 0x18              ;       low page alternate
+       ld bc, #0x7ffd
+       out (c), a
+
+       ld hl, #0x8000                  ;       Fixed
+       ld de, #0xC000                  ;       Page we just mapped in
+       ld bc, #16384
+       ldir
 
        ; Copy done
 
@@ -242,11 +274,22 @@ _dofork:
        ld bc, #U_DATA__TOTALSIZE
        ldir
 
+       ;
+       ; And back into the child
+       ;
        ld bc, #0x7ffd
        ld a, (current_map)
        out (c), a
         ; now the copy operation is complete we can get rid of the stuff
         ; _switchin will be expecting from our copy of the stack.
+
+       ;
+       ; FIXME: at this point we may need to swap the page ptrs of the parent
+       ; and child so that we end up with the right one owning 0x8000.
+       ; Either that or we make the switchin/switchout intelligent about
+       ; the exchange on a task switch over.
+       ;
+
         pop bc
         pop bc
         pop bc
@@ -281,14 +324,9 @@ _dofork:
 ;      Note: this needs reviewing. We now have a lot more program memory
 ;      we can use with a lazy copying model
 ;
-;
-;      FIXME: need to make this copy 0xC000-0xFFFF bank to bank
-;      and 0x8000 to the other bank
-;
 bankfork:
-;      ld bc, #(0x4000 - 768)          ;       16K minus the uarea stash
-
-       ld b, #0x3D             ; 40 x 256 minus 3 sets for the uarea stash
+       or #0x18                ; ROM bits for the bank
+       ld b, #0x3C             ; 40 x 256 minus 4 sets for the uarea stash/irqs
 bankfork_1:
        ld hl, #0xC000          ; base of memory to fork (vectors included)
        push bc                 ; Save our counter and also child offset
@@ -306,6 +344,7 @@ bankfork_1:
        ld a, c                 ; switch to the child
        push bc                 ; save the bank pointers
        ld bc, #0x7ffd
+       or #0x18                ; ROM bits
        out (c), a
        ld hl, #bouncebuffer
        ld bc, #256
@@ -316,7 +355,42 @@ bankfork_1:
        pop bc
        djnz bankfork_1         ; rinse, repeat
        ret
+;
+;      Flip low banks over. Interrupts must be off as the low banks don't
+;      have the IM2 vectors
+;
+fliplow:
+       exx
+       ld hl, #0x8000
+       ld de, #0xc000
+       ld a, #6 + 0x18
+       ld bc, #0x7ffd
+       out (c), a
+       ;
+       ;       No stack use between here and restoring the map
+       ;
+flip2:
+       ld b, #0                ; 16K in 256 bytes
+flip1:
+       ld c, (hl)
+       ld a, (de)
+       ex de, hl
+       ld (hl), c
+       ld (de), a
+       inc hl
+       inc de
+       djnz flip1
+       xor a
+       cp d                    ; Wrapped to 0x0000 ?
+       jr nz, flip2
 
+       ld a, (current_map)
+       ld bc, #0x7ffd
+       out (c), a
+       exx
+       ld a, (hl)              ; Update low bank number
+       ld (low_bank), a
+       ret
 ;
 ;      For the moment
 ;
@@ -328,3 +402,5 @@ bouncebuffer:
 ;      a true common so it's even easier. We never use both at once
 ;      so share with bouncebuffer
 _swapstack:
+low_bank:
+       .db 0