From: Alan Cox <alan@linux.intel.com>
Date: Sat, 20 May 2017 18:14:56 +0000 (+0100)
Subject: v68: do some updating on the in progress banked memory model
X-Git-Url: https://git.ndcode.org/public/gitweb.cgi?a=commitdiff_plain;h=9c9285e5d7cebe274c7cbf6f7ed5018b5f813e97;p=FUZIX.git

v68: do some updating on the in progress banked memory model
---

diff --git a/Kernel/platform-v68-banked/p68000.S b/Kernel/platform-v68-banked/p68000.S
index 9a8d6fd5..f12371a7 100644
--- a/Kernel/platform-v68-banked/p68000.S
+++ b/Kernel/platform-v68-banked/p68000.S
@@ -29,14 +29,14 @@ init_early:
 ;	FIXME: could be in discard if we wanted
 ;
 init_hardware:
-            ; set system RAM size(hadcode hacks for now) 
+            ; set system RAM size(hardcode hacks for now)
 	    move.w #512,d0
 	    move.w d0,ramsize
 	    sub.w  #64,d0		; Guess for kernel
 	    move.w d0,procmem		; guesses for now
 
-	    move.l #0,a0
-	    move.w #256,d0
+	    move.l #8,a0
+	    move.w #253,d0
 	    move.l #unexpected,d1
 init_trap_loop:
 	    move.l d1,(a0)+
@@ -81,9 +81,6 @@ timer_irq:
 	    clr.b U_DATA__U_ININTERRUPT(a5)
 	    move.b $00F04000,d0		; Re-enable
 
-	    ; DEBUG FIXME
-	    bra no_signal
-
 	    tst.b U_DATA__U_INSYS(a5)
 	    bne no_preempt
 	    tst.b need_resched
@@ -121,14 +118,24 @@ program_vectors:
 	    rts
 
 ;
-;	TODO
+;	Switch the banking hardware.
 ;
 map_process_always:
+	; make sure the current process is mapped.
+	move.b U_DATA__U_PAGEB(a5),$00F05000
+	rts
 map_process:
-map_kernel:
+	; map a specific process (not actually used)
+	move.b P_TAB__P_PAGE_OFFSETB(a5),$00F05000
+	rts
 map_restore:
+	move.b $00F05000,banksave
+	rts
 map_save:
-	    rts
+	move.b banksave,$00F05000
+	rts
+map_kernel:				; we never bank out the kernel
+	rts
 
 ; outchar: Wait for UART TX idle, then print the char in d0
 
@@ -143,7 +150,8 @@ outcharw:
 	    rts
 
 ;
-;	IDE
+;	IDE. This differs a tiny bit from the simple case because we must
+;	support bank switching while handling swap.
 ;
 devide_read_data:
 	move.l blk_op,a0
@@ -189,3 +197,4 @@ vdso:	trap #14		; syscall entry
 .section data
 
 kernel_flag: byte 1
+banksave:    byte 0
diff --git a/Kernel/platform-v68-banked/tricks.S b/Kernel/platform-v68-banked/tricks.S
index 9c02a660..fcc00022 100644
--- a/Kernel/platform-v68-banked/tricks.S
+++ b/Kernel/platform-v68-banked/tricks.S
@@ -1,10 +1,31 @@
 #include "../kernel-68000.def"
 #include "kernel.def"
 
-
 .globl switchout,switchin,dofork,udata_shadow,udata_stash
 
+
 .mri 1
+;
+;	There are two ways a banked 68K system can handle the udata pointer.
+;	The first is to keep an array of udata objects in the kernel space
+;	and flip a5, the other is to copy the udata to and from a save area
+;	in the banks as we do on 8bit. The former is far faster but the
+;	latter is useful if you have a limited area of protected memory for
+;	the kernel.
+;
+;	For the virtual platform we use the stash because of the limited
+;	protected area. In the multiple udata case dofork instead needs to
+;	- push a switchin frame
+;	- save the state in its udata as it would with a switchout
+;	- copy the udata state to the child
+;	- call newproc(child) with udata ptr pointing to the child
+;	- clear runticks
+;	- mark itself running
+;	- build a top of supervisor frame to return to userspace
+;	- move stack up to it
+;	- clear registers
+;	- restore user a5
+;	- rte
 
 ; Switchout switches out the current process, finds another that is READY,
 ; possibly the same process, and switches it in.  When a process is
@@ -22,7 +43,8 @@ switchout:
 	movem.l a0/a2-a4/a6/d2-d7,-(sp)
 	move.l sp,U_DATA__U_SP(a5)	; this is where the SP is restored in switchin
 	;
-	; keep a fast path for wakeup of the last executed process
+	; keep a fast path for wakeup of the last executed process. We don't
+	; need the fastpaths if not copying udata buffers.
 	;
 	tst.b nready
 	bne slow_path
@@ -138,8 +160,8 @@ switchinfail:
         bra trap_monitor
 
 	;
-	; this gets exciting on the 68000 because our udata is not in a
-	; fixed location except for swap only platforms. That means any
+	; this gets exciting on the 68000 because our udata is not always in
+	; a fixed location except for swap only platforms. That means any
 	; udata relative pointers on the stack when we duplicate the kernel
 	; stack point to the parent. For the simple case we have a single
 	; swapped udata and stack so all is fairly easy. For the other
@@ -168,20 +190,43 @@ dofork:
 	; offset
 
 	;
-	; Set up a switchin frame for the parent process
+	; Set up a switchin frame for the parent process and ensure the
+	; parent state is valid
 	;
 	move.w P_TAB__P_PID_OFFSET(a0),-(sp)	;	child pid (parent return)
 	move.l usp,a0
 	movem.l a0/a2-a4/a6/d2-d7,-(sp)	;	save state
 	move.l sp,U_DATA__U_SP(a5)	;	save pointer
+	;
+	; At this point we can make a copy of the parent udata into the
+	; stash and it will be valid
 
 	move.l a0,-(sp)			;	argument to newproc
+
+	;
+	; Save the parent into the udata stash
+	;
+	lea.l udata_stash,a0
+	move.l a5,a1
+	move.w #255,d0
+	; FIXME - optimise 1K copy
+copyif:	move.l (a1)+,(a0)+
+	dbra d0,copyif
+
+	move.l (sp),a0
 	move.w P_TAB__P_PAGE_OFFSET(a0),d0	; page
 
+	;
+	;	Copy the banks over
+	;
+
 	jsr bankfork			;	copy the memory
 
 	move.l (sp),a0
 	
+	;
+	;	We enter this on the child's mappings with its udata
+	;
 	jsr newproc			;	Called with the child udata
 	add.w #54,sp			;	toss the stack frames