tgl6502: Work on execve, also jump to monitor on crashes

diff --git a/Kernel/platform-tgl6502/tgl6502.s b/Kernel/platform-tgl6502/tgl6502.s
index a1ba693..330f15b 100644 (file)
--- a/Kernel/platform-tgl6502/tgl6502.s
+++ b/Kernel/platform-tgl6502/tgl6502.s
@@ -52,8 +52,17 @@ syscall           =  $FE
 
 nmi_trap:
 _trap_monitor:
+;
+;      Put the ROM back as it was at entry including the second 8K bank we
+;      only use for vectors, then jump to $E000 which should enter whatever
+;      monitor was put there.
+;
            sei
-           jmp _trap_monitor
+           ldx #$40
+           stx $FF90           ; $C000
+           inx
+           stx $FF91           ; $E000
+           jmp $E000
 
 _trap_reboot:
            jmp _trap_reboot    ; FIXME: original ROM map and jmp
@@ -113,14 +122,17 @@ _program_vectors:
            ; just pass it on
            jsr map_process
 program_vectors_k:
-           lda #<vector
-           sta $FFFE
-           lda #>vector
-           sta $FFFF
-           lda #<nmi_handler
-           sta $FFFA
-           lda #>nmi_handler
-           sta $FFFB
+;
+;      These are in common ROM space in our case
+;
+;          lda #<vector
+;          sta $FFFE
+;          lda #>vector
+;          sta $FFFF
+;          lda #<nmi_handler
+;          sta $FFFA
+;          lda #>nmi_handler
+;          sta $FFFB
            ; However tempting it may be to use BRK for system calls we
            ; can't do this on an NMOS 6502 because the chip has brain
            ; dead IRQ handling bits that could simply "lose" the syscall!
@@ -311,12 +323,11 @@ vector:
            pha
            tsx                                 ; and save the 6502 stack ptr
            stx istack_switched_sp              ; in uarea/stacks
-
 ;
-;      Hope the user hasn't gone over 192 bytes of 6502 stack !
+;      Hope the user hasn't used all the CPU stack
 ;
-           ldx #$40                            ; guess at reserving some istack
-           txs                                 ; our istack
+;      FIXME: we should check here if S is too low and if so set it high
+;      and deliver SIGKILL
 ;
 ;      Configure the C stack to the i stack
 ;
@@ -362,13 +373,13 @@ syscall_entry:
 
            ldy #0
 
-copy_args:  lda (ptr1),y       ; copy the arguments from current bank
-           sta (ptr2),y        ; will write into bank 1
+copy_args:  lda (ptr1),y       ; copy the arguments over
+           sta (ptr2),y
            iny
            cpy #8
            bne copy_args
            ;
-           ; Now we need to bank and stack switch
+           ; Now we need to stack switch
            ;
            lda sp
            pha
@@ -377,13 +388,14 @@ copy_args:  lda (ptr1),y  ; copy the arguments from current bank
            tsx
            stx U_DATA__U_SP
 ;
-;      We try and divide our previous stack resource up between user
-;      and kernel. It's not clear if we should do this, copy the stack
-;      or do something clever I've not thought of yet. Possibly we should
-;      see if there is enough stack and if not copy and screw about ?
+;      We save a copy of the high byte of sp here as we may need it to get
+;      the brk() syscall right.
+;
+           sta U_DATA__U_SP + 1
+;
 ;
-           ldx #$80
-           txs                 ; Switch to the working stack
+;      FIXME: we should check here if there is enough 6502 stack left
+;      and if so either copy and switch stacks or kill the process
 ;
 ;      Set up the C stack
 ;
@@ -419,7 +431,7 @@ copy_args:  lda (ptr1),y    ; copy the arguments from current bank
            pla
            sta ptr1+1
            pla
-           sta ptr1+1
+           sta ptr1
 ;
 ;      Copy the return data over
 ;
@@ -445,9 +457,24 @@ copy_args:  lda (ptr1),y   ; copy the arguments from current bank
 
 
 platform_doexec:
+;
+;      Start address of executable
+;
            stx ptr1+1
            sta ptr1
-           jmp (ptr1)          ; 0x2000 usually
+;
+;      Set up the C stack
+;
+           lda U_DATA__U_ISP
+           sta sp
+           lda U_DATA__U_ISP+1
+            sta sp+1
+;
+;      Set up the 6502 stack
+;
+           ldx #$ff
+           txs
+           jmp (ptr1)          ; Enter user application
 
 ;
 ;      Straight jumps no funny banking issues