6502: first cut at sorting the pre-emption fun out

diff --git a/Kernel/platform-v65/v65.s b/Kernel/platform-v65/v65.s
index ba5e0a9..7280122 100644 (file)
--- a/Kernel/platform-v65/v65.s
+++ b/Kernel/platform-v65/v65.s
@@ -325,19 +325,54 @@ vector:
 ;
 ;      TODO: pre-emption
 ;
+           lda _need_resched
+           beq no_preempt
 
+           lda #0
+           sta _need_resched
 
+           ; Switch to our kernel stack which is free as we don't preempt
+           ; from kernel space
+           tsx
+           stx U_DATA__U_SYSCALL_SP
+           ldx #kstack_top
+           txs
 
+           ;
+           ; TODO: do we need to sort the C stack or is it sufficient to
+           ; just do the 6502 stack at this point since we have a valid
+           ; C stack.. the IRQ one for chksigs to run, while the
+           ; platform_switchout code is asm only as we switch in ?
+           ;
+           lda #1
+           sta U_DATA__U_INSYS
+           jsr _chksigs
+           ; Mark ourselves Ready not Running
+           ldx U_DATA__U_PTAB
+           lda #P_READY
+           sta a:P_TAB__P_STATUS_OFFSET,x
+           ; Switch out .. we will re-appear at some point
+           lda U_DATA__U_PTAB
+           ldx U_DATA__U_PTAB+1
+           jsr _platform_switchout
+           ;
+           ; Now return to the old state having woken back up
+           ; Clear insys, move back onto the interrupt stack
+           ;
+           lda #0
+           sta U_DATA__U_INSYS
+           ldx #U_DATA__U_SYSCALL_SP
+           txs
+           ;
+           ; Check what signals are now waiting for us
+           ;
+no_preempt:
 ;
 ;      Signal handling on 6502 is foul as the C stack may be inconsistent
 ;      during an IRQ. We push a new complete rti frame below the official
 ;      one, along with a vector and the signal number. The glue in the
 ;      app is expected to switch to a signal stack or similar, pop the
 ;      values, invoke the signal handler and then return.
-;
-;      FIXME: at the moment the irqout path will not check for multiple
-;      signals so the next one gets delivered next irq.
-;
 ;
            lda U_DATA__U_CURSIG
            beq irqout