z80fixedbank: experimentally enable interrupts for swapper

Note also we should now be able to sort out fork()

diff --git a/Kernel/lib/z80fixedbank.s b/Kernel/lib/z80fixedbank.s
index 511405a..debcc06 100644 (file)
--- a/Kernel/lib/z80fixedbank.s
+++ b/Kernel/lib/z80fixedbank.s
@@ -14,7 +14,6 @@
         .globl _getproc
         .globl _trap_monitor
         .globl trap_illegal
-        .globl _inint
         .globl _switchout
         .globl _switchin
         .globl _doexec
@@ -139,11 +138,23 @@ _switchin:
        or a
        jr nz, not_swapped
 
+       ;
+       ;       Re-enable interrupts while we swap. This is ok because
+       ;       we are not on the IRQ stack when switchin is invoked.
+       ;
+       ;       There are two basic cases
+       ;       #1: pre-emption. Not in a system call, must avoid
+       ;       re-entering pre-emption logic, Z80 lowlevel code sets U_INSYS
+       ;       #2: kernel syscall. Also protected by U_DATA__U_INSYS
+       ;
+       ei
        push hl
        push de
        call _swapper
        pop de
        pop hl
+       di
+
        ld a, (hl)
 not_swapped:
        ld hl, (U_DATA__U_PTAB)
@@ -219,6 +230,10 @@ _dofork:
         ; always disconnect the vehicle battery before performing maintenance
         di ; should already be the case ... belt and braces.
 
+       ;
+       ; FIXME: we should no longer need interrupts off for most of a
+       ; fork() call.
+       ;
         pop de  ; return address
         pop hl  ; new process p_tab*
         push hl