Fix software pointer being enabled when it isn't needed. Improve HangWatch support.

Detail:
  s/vdu/vdupointer - For any mode where the software pointer is usable, RestorePointer was restoring the software pointer regardless of whether it was in use at the time RemovePointer was called. This would cause both the software & hardware pointers to be briefly enabled at the same time, potentially causing flickering or other glitches. Fix the issue by making sure RestorePointer only restores if the software pointer was actually in use at the time RemovePointer was called. Also, attempt to deal with the situation where the pointer might have moved to a location where the software pointer is no longer required.
  s/Middle - Improve integration of HangWatch with the abort handler - avoid overwriting the top of the SVC stack so that it can be preserved for the HangWatch dump.
Admin:
  Tested on Raspberry Pi


Version 5.35, 4.79.2.270. Tagged as 'Kernel-5_35-4_79_2_270'

VersionASM

@@ -13,11 +13,11 @@
                         GBLS    Module_ComponentPath
 Module_MajorVersion     SETS    "5.35"
 Module_Version          SETA    535
-Module_MinorVersion     SETS    "4.79.2.269"
-Module_Date             SETS    "10 Jul 2015"
-Module_ApplicationDate  SETS    "10-Jul-15"
+Module_MinorVersion     SETS    "4.79.2.270"
+Module_Date             SETS    "13 Jul 2015"
+Module_ApplicationDate  SETS    "13-Jul-15"
 Module_ComponentName    SETS    "Kernel"
 Module_ComponentPath    SETS    "castle/RiscOS/Sources/Kernel"
-Module_FullVersion      SETS    "5.35 (4.79.2.269)"
-Module_HelpVersion      SETS    "5.35 (10 Jul 2015) 4.79.2.269"
+Module_FullVersion      SETS    "5.35 (4.79.2.270)"
+Module_HelpVersion      SETS    "5.35 (13 Jul 2015) 4.79.2.270"
                         END

VersionNum

@@ -5,19 +5,19 @@
  *
  */
 #define Module_MajorVersion_CMHG        5.35
-#define Module_MinorVersion_CMHG        4.79.2.269
-#define Module_Date_CMHG                10 Jul 2015
+#define Module_MinorVersion_CMHG        4.79.2.270
+#define Module_Date_CMHG                13 Jul 2015
 
 #define Module_MajorVersion             "5.35"
 #define Module_Version                  535
-#define Module_MinorVersion             "4.79.2.269"
-#define Module_Date                     "10 Jul 2015"
+#define Module_MinorVersion             "4.79.2.270"
+#define Module_Date                     "13 Jul 2015"
 
-#define Module_ApplicationDate          "10-Jul-15"
+#define Module_ApplicationDate          "13-Jul-15"
 
 #define Module_ComponentName            "Kernel"
 #define Module_ComponentPath            "castle/RiscOS/Sources/Kernel"
 
-#define Module_FullVersion              "5.35 (4.79.2.269)"
-#define Module_HelpVersion              "5.35 (10 Jul 2015) 4.79.2.269"
+#define Module_FullVersion              "5.35 (4.79.2.270)"
+#define Module_HelpVersion              "5.35 (13 Jul 2015) 4.79.2.270"
 #define Module_LibraryVersionInfo       "5:35"

s/Middle

@@ -712,12 +712,13 @@ UNDEF2
         MOV     R14, R4                 ; corrupt R14_SVC (but already saved if we were in SVC)
 ; ... and fall into
 UNDEF1
-        LDR     sp, =SVCSTK             ; Flatten superstack
-
       [ HangWatch
+        LDR     sp, =SVCSTK-SVCStackSize+512 ; HangWatch doesn't need much stack space, so use the low part, as it's the area that's least likely to contain something useful to the dump
         SWI     &59283                  ; XHangWatch_Dump
       ]
 
+        LDR     sp, =SVCSTK             ; Flatten superstack
+
         ; Check that ExceptionDump is safe to use
         Push    "R14"                   ; Preserve error ptr
         LDR     R4, =ZeroPage

s/vdu/vdupointer

@@ -632,12 +632,19 @@ RemovePointer ROUT
         BNE     %FT90
         ; Lock mutex
         MOV     r10, #1
-        STRB    r10, [WsPtr, #SWP_Restore]
         STRB    r10, [WsPtr, #SWP_Mutex]
-        ; Remove pointer if possible
+        ; We need to set SWP_Restore so that we know to release the mutex once we're done
+        ; However if the software pointer currently isn't visible (hardware pointer in use) then there might not be an image to restore
+        ; So SWP_Restore can take three values:
+        ; 0 -> not in RemovePointer block
+        ; 1 -> in RemovePointer but no restore needed
+        ; 2 -> in RemovePointer and restore needed
         LDR     r11, [WsPtr, #SWP_Pos]
-        LDR     r10, [WsPtr, #SWP_Under]
         TEQ     r11, #0
+        MOVNE   r10, #2
+        STRB    r10, [WsPtr, #SWP_Restore]
+        ; Remove pointer if necessary
+        LDRNE   r10, [WsPtr, #SWP_Under]
         BLNE    RemoveSoftwarePointer
         ; Exit with mutex still locked
 90
@@ -651,13 +658,16 @@ RemovePointer ROUT
 ;       Software pointer restore assumed to be needed
 
 RestorePointer ROUT
-        STMFD   R13!,{R0-R6,R14}
+        STMFD   R13!,{R0-R7,R14}
+        PHPSEI  R7                           ; IRQs off while we work out what to do
+        LDRB    R1, [WsPtr, #SWP_Restore]
         MOV     R0, #0
         STRB    R0, [WsPtr, #SWP_Restore]
         STRB    R0, [WsPtr, #SWP_Mutex]
         LDRB    R6, [WsPtr, #PointerShapeNumber]
-        ANDS    R6, R6, #&7F
-        BEQ     %FT10
+        TST     R1, #2                       ; Was the software pointer actually on?
+        ANDNES  R6, R6, #&7F
+        BEQ     %FT90
 
         ADD     R3, WsPtr, #PointerShapes-4
         LDR     R3, [R3, R6, LSL #2]         ; R3 -> current shape block (R6 = shape 1..4)
@@ -683,9 +693,47 @@ RestorePointer ROUT
         LDRB    R4, [R3, #PointerActiveY]
         SUB     R2, R2, R4                         ; R2 = pointer y, adjusted for active point
 
+        ; The pointer may have moved while we had it disabled.
+        ; If it has moved, it's possible the hardware pointer has taken over
+        ; and the software pointer isn't needed anymore
+        ; Potentially we could deal with this inside UpdateSoftwarePointer
+        ; (i.e. cache the new parameters if it gets called with the mutex
+        ; locked), but that will add a fair bit of complexity. So for now go
+        ; with the simpler approach of comparing the current position against
+        ; the last position used by the software pointer and calling through to
+        ; GraphicsV if it's changed (otherwise, call software pointer directly)
+
+      [ NoARMv6
+        MOV     R5, R1, LSL #16
+        MOV     LR, R2, LSL #16
+        ORR     R5, LR, R5, LSR #16
+      |
+        PKHBT   R5, R1, R2, LSL #16
+      ]
+        LDR     LR, [WsPtr, #SWP_Coords]
+        TEQ     LR, R5
+        BEQ     %FT50
+
+        ; Pointer has moved - call GraphicsV
+        LDR     R4, [WsPtr, #CurrentGraphicsVDriver]
+        MOV     R4, R4, LSL #24
+        ORR     R4, R4, #GraphicsV_UpdatePointer
+        BL      CallGraphicsV
+
+        TEQ     R4, #0
+        BEQ     %FT90
+
+50
+        ; IRQs on for software pointer call
+        ; This does open up the possibility for the pointer shape/location to
+        ; change under IRQ while we're still rendering it - so a more advanced
+        ; locking mechanism may be desirable in future
+        PLP     R7
+
         BL      UpdateSoftwarePointer
-10
-        LDMFD   R13!,{R0-R6,PC}
+90
+        PLP     R7
+        LDMFD   R13!,{R0-R7,PC}
 
 ; *****************************************************************************
 ;