zx128: fix banking returns through common and discard

With this little gem fixed we can now get all the way through the IDE probe
in banked code and to the bootdev prompt.

diff --git a/Kernel/platform-zx128/zx128.s b/Kernel/platform-zx128/zx128.s
index 0bcbb58..26a5477 100644 (file)
--- a/Kernel/platform-zx128/zx128.s
+++ b/Kernel/platform-zx128/zx128.s
@@ -281,13 +281,17 @@ bankina0:
        ld d, (hl)
        inc hl
        push hl            ; Restore corrected return pointer
+       ld bc, (current_map)    ; get current bank into B
        call switch_bank   ; Move to new bank
-       ex de, hl
-       call callhl        ; can't optimise - we need the stack depth right
-       ret
-callhl:        jp (hl)            ; calls from bank 0 are different to the others
-                          ; we started in common so we don't need to map
-                          ; the old state back
+       ; figure out which bank to map on the return path
+       ld a, c
+       or a
+       jr z, __retmap1
+       dec a
+       jr z, __retmap2
+       jr __retmap3
+
+callhl:        jp (hl)
 __bank_0_2:
        ld a, #1           ; logical 2 -> physical 1
        jr bankina0
@@ -305,6 +309,7 @@ bankina1:
        inc hl
        push hl            ; Restore corrected return pointer
        call switch_bank   ; Move to new bank
+__retmap1:
        ex de, hl
        call callhl        ; call the function
        xor a              ; return to bank 1 (physical 0)
@@ -323,6 +328,7 @@ bankina2:
        inc hl
        push hl            ; Restore corrected return pointer
        call switch_bank   ; Move to new bank
+__retmap2:
        ex de, hl
        call callhl        ; call the function
        ld a, #1           ; return to bank 2
@@ -340,6 +346,7 @@ bankina3:
        inc hl
        push hl            ; Restore corrected return pointer
        call switch_bank   ; Move to new bank
+__retmap3:
        ex de, hl
        call callhl        ; call the function
        ld a, #7           ; return to bank 0
@@ -352,6 +359,11 @@ __bank_3_2:
 ;
 ;      Stubs from common are the easy case and use HL
 ;
+;      FIXME: if we ever stub a function that is in discard/common and
+;      which calls into code that bank switches then returns this will
+;      break. If that happens then these will need munging into the
+;      method used in __bank_0_x (ick)
+;
 __stub_0_1:
        xor a
        call switch_bank