tgl6502: first cut at a sane syscall ABI

diff --git a/Kernel/platform-tgl6502/tgl6502.s b/Kernel/platform-tgl6502/tgl6502.s
index 330f15b..688002c 100644 (file)
--- a/Kernel/platform-tgl6502/tgl6502.s
+++ b/Kernel/platform-tgl6502/tgl6502.s
@@ -37,6 +37,8 @@
            .import _kernel_flag
            .import copycommon
 
+           .import incaxy              ; from the C runtime
+
             .include "kernel.def"
             .include "../kernel02.def"
            .include "zeropage.inc"
@@ -353,33 +355,51 @@ irqout:
            pla
            rti
 
-
-;          X, A holds the syscall block
-;          Y holds the call code
-;          We assume the kernel is in bank 0
+;
+;          sp/sp+1 are the C stack of the userspace
+;          with the syscall number in X
+;          Y indicates the number of bytes of argument
 ;
 syscall_entry:
+           php
            sei
-           sty U_DATA__U_CALLNO
-           pha
-           txa
-           pha
-           sta ptr1
-           stx ptr1+1
-           lda #<U_DATA__U_ARGN
-           sta ptr2
-           lda #>U_DATA__U_ARGN
-           sta ptr2+1
+           cld
+
+           stx U_DATA__U_CALLNO
+
+           ; Remove the arguments. This is fine as by the time we go back
+           ; to the user stack we'll have finished with them
+           lda sp
+           ldx sp+1
+           jsr incaxy
+           sta sp
+           stx sp+1
 
            ldy #0
+           ;
+           ;   We copy the arguments but need to deal with the compiler
+           ;   stacking in the reverse order. At this point ptr1 points
+           ;   to the last byte of the arguments (first argument). We go
+           ;   down the stack copying words up the argument list.
+           ;
 
-copy_args:  lda (ptr1),y       ; copy the arguments over
-           sta (ptr2),y
+copy_args:
+           lda (ptr1),y                ; copy the arguments over
+           sta U_DATA__U_ARGN,x
            iny
+            inx
+           lda (ptr1),y
+           sta U_DATA__U_ARGN,x
+            iny
+            dex
+            dex
+           dex
            cpy #8
            bne copy_args
+
            ;
-           ; Now we need to stack switch
+           ; Now we need to stack switch. Save the adjusted stack we want
+           ; for return
            ;
            lda sp
            pha
@@ -428,33 +448,22 @@ copy_args:  lda (ptr1),y  ; copy the arguments over
            sta sp+1
            pla
            sta sp
-           pla
-           sta ptr1+1
-           pla
-           sta ptr1
-;
-;      Copy the return data over
-;
-           ldy #8              ; write them after the argument block
-           lda U_DATA__U_ERROR
-
-           sta (ptr1), y
-           iny
-           lda U_DATA__U_ERROR+1
-           sta (ptr1),y
-           iny
-           lda U_DATA__U_RETVAL
-           sta (ptr1),y
-           iny
-           lda U_DATA__U_RETVAL+1
-           sta (ptr1), y
 ;
 ;      FIXME: do signal dispatch - this will need C stack fixing, and
 ;      basically signal dispatch is __interrupt.
 ;
+;      We may be in decimal mode beyond this line.. take care
+;
+           plp
 
-           rts
+;      Copy the return data over
+;
+           ldy U_DATA__U_RETVAL
+           ldx U_DATA__U_RETVAL+1
+;      Also sets Z for us
+           lda U_DATA__U_ERROR
 
+           rts
 
 platform_doexec:
 ;