From: Alan Cox <alan@linux.intel.com>
Date: Sat, 21 Oct 2017 12:50:06 +0000 (+0100)
Subject: 8086: sketch out tricks.S for this platform
X-Git-Url: https://git.ndcode.org/public/gitweb.cgi?a=commitdiff_plain;h=7ca0ac64582d5d1096cfa8d28b80e688d13cbd9e;p=FUZIX.git

8086: sketch out tricks.S for this platform
---

diff --git a/Kernel/platform-ibmpc/tricks.S b/Kernel/platform-ibmpc/tricks.S
index 55be713a..84fbbee7 100644
--- a/Kernel/platform-ibmpc/tricks.S
+++ b/Kernel/platform-ibmpc/tricks.S
@@ -1,5 +1,9 @@
 #include "../kernel-8086.def"
 
+/*
+ *	How to deal with EMM remains an interesting discussion point
+ */
+
 	.arch i8086,jumps
 	.code16
 	.att_syntax prefix
@@ -10,43 +14,169 @@
 	.globl switchout
 	.globl dofork
 
+
+	/* udata transfer functions */
+
+	/* Move the udata for for udata.u_ptab into the process save slot.
+	   Preserve bx. We keep udata's in a buffer but that buffer can
+	   live outside the kernel so udata_ds may not be in kernel_ds
+
+	   All our callers don't mind us trashing es/di/cx
+
+	   NOTE: Breaks if we exceeed 128 processes */
+stash_udata:
+	/* TODO */
+	movw P_TAB__P_PAGE(%bx),%al
+	addb %al,%al
+	xchg %al,%ah		/* will be 00xx, want xx00 */
+	pushw %es
+	movw %ax,di
+	movw udata_ds,%ax
+	movw %ax,%es
+	movw udata,%si
+	movw $256,%cx
+	cld
+	rep movsw
+	popw %es
+	ret
+
+	/* Restore the udata for process %bx, preserve %bx */
+restore_udata:
+	movb P_TAB__P_PAGE(%bx),%al
+	addb %al,%al
+	xchg %al,%ah
+	pushw %ds
+	movw %ax,%si
+	movw udata_ds,%ax
+	movw udata,%di
+	movw %ax,%ds
+	movw $256,%cx
+	cld
+	rep movsw
+	popw %ds
+	ret
+
+	/* udata.u_ptab is the parent, %bx the child, preserve %bx */
+fork_copy:
+	/* Copy the data from the current instance into the new one
+	   BEWARE: it is possible in the EMM case that the two processes
+	   data will be in EMM in the same segment. In fact it's likely to
+	   be the case. We need an optimised copier and EMM help for this
+	   to do split maps (32K/32K) and blast two lots of 32K */
+	ret
+
+	/* Called to give up processor time. We will pop out of this in
+	   potentially some other process, but we might also come back
+	   directly */
 switchout:
 	cli
 	call chksigs
-	pushw %ax		/* Figure out what we actually need to save */
-	pushw %bx
-	pushw %cx
-	pushw %dx
-	pushw %es
+	movb nready,%al
+	cmpb $1,%al
+	bne slow_path
+idling:
+	sti
+	call platform_idle
+	cli
+	movb nready,%al
+	cmpb $0,%al
+	je idling
+
+	/* Ok there is something to run - but is it us ? */
+	cmpb $1,%al
+	jne slow_path
+
+	/* Fast path out */
+	ret
+
+slow_path:
+	xorw %ax,%ax
+	pushw %ax
+	pushw %ei
 	pushw %di
 	pushw %bp
 	movw %sp,udata+U_DATA__U_SP
+
+	call stash_udata	
+
 	call getproc
 	push %ax
 	call switchin
 	jmp trap_monitor
 
 switchin:
-	push %bp
+	/* We can trash registers here because we'll restore them
+	   for the process we return as */
 	mov %sp,%bp
 	cli
-	movw 4(%bp),%si
-	cmpb $0,P_TAB__P_PAGE_OFFSET(%si)
-	/*
+	movw 2(%bp),%bx
+	/* No MMU pointer means we are swapped out */
+	movw P_TAB__P_PAGE_OFFSET+2(%bx),%si
+	/* si is now our MMU pointer or 0 */
+	cmpw $0,%si
 	jne not_swapped
-	 TODO */
+	/* TODO */
+	movw P_TAB__P_PAGE_OFFSET+2(%bx),%si
+not_swapped:
+	cmpw udata+U_DATA__U_PTAB,%bx
+	je skip_copyback	/* this can happen even with idle optimisation
+				   consider two processes ready and us winning */
+	call restore_udata
+	cmpw udata+U_DATA__U_PTAB,%bx
+	jne switchfail
+skip_copyback:
+	movb $P_RUNNING,P_TAB__P_STATUS_OFFSET(%bx)
+	xorw %ax,%ax
+	movw %ax,runticks
+	movw udata+U_DATA__U_SP,%sp
+	popw %bp
+	popw %di
+	popw %ei	
+	popw %ax
 	ret
 switchfail:
-/*	call  outaxhex
+	call  outaxhex
 	mov $badswitchmsg,ax
 	calloutstring		
-	jmp _trap_monitor */
-
+	jmp _trap_monitor
 dofork:
-	/* TODO */
-	movw $-1,%ax
+	pushw %bp
+	movw %sp,%bp
+	cli
+	movw 4(%bp),%bx
+
+	movw P_TAB__P_PID_OFFSET(%bx),%ax
+	pushw %ax
+	pushw %bp
+	pushw %di
+	pushw %ei
+	movw %sp,udata+U_DATA__U_SP
+
+	/* These two preserve bx */
+	call stash_udata
+
+	/* Stack twice as C code is entitled to mash the first one */
+	pushw %bx
+	pushw %bx
+	call fork_copy
+	popw %bx
+	popw %bx
+
+	popw %ei
+	popw %di
+	popw %bp
+	popw %ax
+
+	pushw %bx
+	call newproc
+	popw %ax
+
+	xorw %ax,%ax		/* As child */
+	movw %ax,runticks
 	ret
 
 	.data
 swapstack:
 	.bss 256
+	.byte "_switchin: FAIL",0
+	.even