65c816: further work on things like return paths and fork() corrections

We still have a weird failure on stat() but a lot more stuff seems to
want to behave now

diff --git a/Kernel/lowlevel-65c816.s b/Kernel/lowlevel-65c816.s
index 8a10c9d..af3f346 100644 (file)
--- a/Kernel/lowlevel-65c816.s
+++ b/Kernel/lowlevel-65c816.s
@@ -44,6 +44,7 @@
        .import platform_doexec
        .import _inint
        .import _trap_monitor
+       .import _switchout
 
        .import push0
        .import incaxy
@@ -233,20 +234,22 @@ noargs:
        pla                             ; pull the saved sp off the ustack
        pla                             ; discard it (it's still fine in
                                        ; bank)
+       rep     #$10
+       .i16
+       lda     U_DATA__U_PAGE
+       tsx
+       sta     3,x
+
+       sep     #$10
+       .i8
 
-       ; We may now be in decimal !
        ldy     U_DATA__U_RETVAL
        ldx     U_DATA__U_RETVAL+1
        ; also sets z for us
        lda     U_DATA__U_ERROR
        pha                             ; save A
 
-       lda     U_DATA__U_PAGE
-       ;
-       ;       We use this trick several times. U_PAGE holds the bank
-       ;       register. As we want our DP to be bank:0000 we need to
-       ;       shift left 8 and add 00 to get our DP value
-       ;
+       lda     U_DATA__U_PAGE          ; so we can set up DP
        pha
        plb                             ; User mapping for data bits
        jsr     setdp                   ; Set DP from A, corrupts A
@@ -276,6 +279,8 @@ noargs:
        ;       rts     in bank return to the interruption point
        ;
 signal_out:
+       .a8
+       .i8
        stz     U_DATA__U_CURSIG
        
        ;
@@ -376,10 +381,11 @@ _doexec:
        ;
        ;       (Will need to change for split I/D)
 
-       lda     U_DATA__U_PAGE  ;       bank
+       lda     U_DATA__U_PAGE  ;       bank for data
        pha                     ;       switch to userdata bank
        plb
 
+       ; lda U_DATA__U_PAGE+1  ;       bank for code
        sty     a:syscall       ;       and in bank:00FE
 
        pha                     ;       stack bank for rtl
@@ -442,7 +448,8 @@ shoot_myself:
        
 ;
 ;      The C world here is fairly ugly. We have to stash various bits of
-;      zero page magic because its not re-entrant.
+;      ZP on a 6502, fortunately on the 65C816 we can have a separate
+;      interrupt DP
 ;
 interrupt_handler:
        ; Make sure we save all of the register bits
@@ -517,8 +524,51 @@ join_interrupt_path:
        .i16
 
 ret_to_user:
-       ; TODO .. pre-emption
+       lda     _need_resched
+       beq     no_preempt
+
+       lda     #0
+       sta     _need_resched
 
+       ldx     istack_switched_sp
+       stx     U_DATA__U_SYSCALL_SP
+       ;
+       ;       Switch to our kernel stack (free because we are not
+       ;       pre-empting in a syscall
+       ;
+       ldx     #kstack_top
+       txs
+       ;
+       ;       Fix up the C stack
+       ;
+       ;
+       ;       Mark ourselves as in a syscall
+       ;
+       lda     #1
+       sta     U_DATA__U_INSYS
+       ;
+       ;       Drop back to a8i8 and schedule ourself out
+       ;
+       sep     #$30
+       .a8
+       .i8
+       lda     U_DATA__U_PTAB
+       ldx     U_DATA__U_PTAB+1
+       jsr     _switchout
+       ;
+       ;       We will (one day maybe) pop back out here. It's not
+       ;       guaranteed (we might be killed off)
+       ;
+       lda     #0
+       sta     U_DATA__U_INSYS
+       ;
+       ;       And exit the handler
+       ;
+       rep     #$10
+
+       .a8
+       .i16
+no_preempt:
        ; Discard saved B and D - for user we will compute the correct
        ; one (we could optimize this a shade and only throw on a
        ; pre-empt FIXME)
@@ -526,7 +576,6 @@ ret_to_user:
        plx
        pla
 
-
        ; Signal return path
        ; The basic idea here is that if a signal is pending we
        ; build a new stack frame under the real one and rti to that. The
@@ -539,13 +588,16 @@ ret_to_user:
        ;       save the bank as a task switch or swap might move the
        ;       process
        ;
-       sep     #$30
-
-       .a8
-       .i8
 
        lda     U_DATA__U_PAGE
 
+       tsx
+       lda     U_DATA__U_PAGE  ;+1 for split ID
+       sta     9,x             ; Might have moved bank if swapping
+
+       sep     #$30
+       .a8
+       .i8
        pha
        plb     ; Now data is the user bank
 
@@ -554,11 +606,10 @@ ret_to_user:
        rep     #$30
        .a16
        .i16
-
        ply
        plx
        pla
-       rti
+       rti                     ; to bank we patched in
 
 ;
 ;      If we hit this we are on the user stack with all kernel mappings
@@ -614,6 +665,7 @@ signal_exit:
        tcs     ; stick y in s
 
        sep     #$20
+       .a8
        pea     sigret_irq      ; signal return
        sep     #$10
        .i8