Be more forgiving of GraphicsV init failures

* Update OS_ScreenMode 11's handling of drivers which fail to
initialise. If there was no previous driver, then instead of trying to
restore that nonexistant driver, stick with the new one. This is mainly
to help with the case where the kernel's built in modes aren't accepted
by the driver, and valid modes only become available once an MDF is
loaded (this can happen with early OMAP3 chip revisions, which have very
tight sync & porch limits, causing 90% of the kernel's modes to be
rejected). If the kernel was to revert to the "no driver" state, then
loading the MDF would still leave you with no video output.
* Since we can now end up in a state where a driver is selected but
hasn't been programmed yet, update OS_Byte 19 to detect this (via the
magic ScreenBlankDPMSState value of 255) and avoid waiting for VSync
* Update RemovePages & InsertRemovePagesExit (screen DA handlers) to
avoid infinite loops if the screen DA gets shrunk to zero size (was seen
while attempting to complete the !Boot sequence while no driver was
active)

Version 6.33. Tagged as 'Kernel-6_33'

VersionASM

@@ -9,12 +9,12 @@
                         GBLS    Module_ApplicationDate
                         GBLS    Module_HelpVersion
                         GBLS    Module_ComponentName
-Module_MajorVersion     SETS    "6.32"
-Module_Version          SETA    632
+Module_MajorVersion     SETS    "6.33"
+Module_Version          SETA    633
 Module_MinorVersion     SETS    ""
-Module_Date             SETS    "19 Jan 2020"
-Module_ApplicationDate  SETS    "19-Jan-20"
+Module_Date             SETS    "12 Feb 2020"
+Module_ApplicationDate  SETS    "12-Feb-20"
 Module_ComponentName    SETS    "Kernel"
-Module_FullVersion      SETS    "6.32"
-Module_HelpVersion      SETS    "6.32 (19 Jan 2020)"
+Module_FullVersion      SETS    "6.33"
+Module_HelpVersion      SETS    "6.33 (12 Feb 2020)"
                         END

VersionNum

-/* (6.32)
+/* (6.33)
  *
  * This file is automatically maintained by srccommit, do not edit manually.
  *
  */
-#define Module_MajorVersion_CMHG        6.32
+#define Module_MajorVersion_CMHG        6.33
 #define Module_MinorVersion_CMHG        
-#define Module_Date_CMHG                19 Jan 2020
+#define Module_Date_CMHG                12 Feb 2020
 
-#define Module_MajorVersion             "6.32"
-#define Module_Version                  632
+#define Module_MajorVersion             "6.33"
+#define Module_Version                  633
 #define Module_MinorVersion             ""
-#define Module_Date                     "19 Jan 2020"
+#define Module_Date                     "12 Feb 2020"
 
-#define Module_ApplicationDate          "19-Jan-20"
+#define Module_ApplicationDate          "12-Feb-20"
 
 #define Module_ComponentName            "Kernel"
 
-#define Module_FullVersion              "6.32"
-#define Module_HelpVersion              "6.32 (19 Jan 2020)"
-#define Module_LibraryVersionInfo       "6:32"
+#define Module_FullVersion              "6.33"
+#define Module_HelpVersion              "6.33 (12 Feb 2020)"
+#define Module_LibraryVersionInfo       "6:33"

hdr/KernelWS

@@ -804,6 +804,7 @@ ScreenBlankDPMSState # 1       ; 0 => just blank video
                                ; 1 => blank to stand-by (hsync off)
                                ; 2 => blank to suspend (vsync off)
                                ; 3 => blank to off (H+V off)
+                               ; 255 => no mode programmed yet
 
         ASSERT  ScreenBlankDPMSState =  Legacy_ScreenBlankDPMSState
         ASSERT ?ScreenBlankDPMSState = ?Legacy_ScreenBlankDPMSState

s/PMF/osbyte

@@ -563,9 +563,11 @@ Osbyte13 ROUT
         TSTNE   R1, #3                  ; NE => blanked and DPMS turned off HSync or VSync
         MyOsbyte NE                     ; if true exit immediately
 
-        ; Also, exit now if we don't have a driver active
+        ; Also, exit now if we don't have a driver active, or there's no
+        ; mode programmed
         LDR     R0, [LR,#CurrentGraphicsVDriver]
         CMP     R0, #GraphicsVInvalid
+        CMPEQ   R1, #255
         MyOsbyte EQ
 
 ; It is actually better to call Idle with interrupts disabled as it stops the interrupt

s/vdu/vdudriver

@@ -106,9 +106,9 @@ VduInit ROUT
         ASSERT (ZeroPage :AND: 255) = 0
         STRB    R0, [R0, #OsbyteVars + :INDEX: VDUqueueItems] ;purge queue
         STRB    R0, [WsPtr, #ScreenBlankFlag]   ; not blanked
-      [ ZeroPage <> 0
+        MOV     R0, #255
+        STRB    R0, [WsPtr, #ScreenBlankDPMSState] ; however, no mode programmed yet
         MOV     R0, #0
-      ]
         STR     R0, [WsPtr, #CursorCounter]
         STR     R0, [WsPtr, #CursorDesiredState]
         STR     R0, [WsPtr, #VduStatus]

s/vdu/vdupalxx

@@ -1064,6 +1064,7 @@ PV_BlankScreen ROUT
         AND     r0, r0, #1
         STRB    r0, [WsPtr, #ScreenBlankFlag]      ; update new state
         LDRB    r1, [WsPtr, #ScreenBlankDPMSState]
+        AND     r1, r1, #3
 
         LDR     r4, [WsPtr, #CurrentGraphicsVDriver]
         MOV     r4, r4, LSL #24

s/vdu/vduswis

@@ -1273,6 +1273,10 @@ RemovePages ROUT
 
 ; display starts in pages that remain
 
+        CMP     R4, #0                  ; if we've somehow shrunk to zero,
+        MOVEQ   R5, R14                 ; then DisplayStart = ScreenEndAddr,
+        BEQ     %FT06                   ; and avoid the infinite loop below!
+
         SUB     R5, R3, R0              ; new DisplayStart
 
 05
@@ -1280,6 +1284,7 @@ RemovePages ROUT
         SUBCS   R5, R5, R4              ; then repeatedly subtract off new size
         BCS     %BT05                   ; until in range
 
+06
         Push    "R0-R2"
         MOV     R0, R5                  ; put new display start in r0
         BL      SetVinit                ; this updates DisplayStart
@@ -1302,10 +1307,15 @@ InsertRemovePagesExit
         LDR     R4, [WsPtr, #DisplayScreenStart]
         SUB     R0, R4, R0
         LDR     R3, [WsPtr, #TotalScreenSize]
+
+        CMP     R3, #0
+        MOVEQ   R0, R14
+        BEQ     %FT26
 25
         CMP     R0, R14                 ; ensure displayscreenstart in range too
         SUBCS   R0, R0, R3
         BCS     %BT25
+26
         BL      NewScreenStart
 30
         BL      SetVendDefault
@@ -2063,6 +2073,10 @@ ScreenMode_SelectDevice ROUT
         MOV     r1, #Service_DisplayChanged
         MOV     r3, #DisplayChangedSub_ModeChanged
         IssueService
+        ; Flag that VSync probably isn't working
+        ; (will be cleared by HardwareModeChange)
+        MOV     r0, #255
+        STRB    r0, [WsPtr, #ScreenBlankDPMSState]
         ; Update current driver VDU var
         STR     r2, [WsPtr, #CurrentGraphicsVDriver]
         ; Issue service call to indicate change is coming
@@ -2071,28 +2085,47 @@ ScreenMode_SelectDevice ROUT
         ; Call InitialiseMode to select a mode to use for this new driver
         CMP     r2, #GraphicsVInvalid
         BLNE    InitialiseMode
-        BVS     %FT15
-        ; Success!
-        MOV     r0, #DisplayChanged_Changed
-        IssueService
-        MOV     r1, r5
-        EXIT
-15
-        ; Something went wrong trying to activate the new driver
-        ; Try and restore the old one
+        BVC     %FT15
+        ; Something went wrong trying to activate the new driver.
+        ; Make sure the VSync flag is still set.
+        MOV     lr, #255
+        STRB    lr, [WsPtr, #ScreenBlankDPMSState]
+        ; Do we have an old driver we can try and switch back to?
+        ;
+        ; If we don't have an old driver, just stick with this new
+        ; one, under the assumption that the failure was because we
+        ; couldn't find a valid mode to switch to (which is generally
+        ; the only way in which InitialiseMode will fail). For such a
+        ; situation, there's a reasonable chance that things will start
+        ; working later on during the boot sequence, e.g. once an MDF
+        ; is loaded. And for such a case, temporarily having a broken
+        ; driver active is much better than restoring the "no driver"
+        ; state, since we currently don't have any kind of watchdog which
+        ; will kick the video system into life once the MDF does get
+        ; loaded.
+        CMP     r5, #GraphicsVInvalid
+        BEQ     %FT15
         STR     r0, [sp] ; Return the error to the caller
         STR     r5, [WsPtr, #CurrentGraphicsVDriver]
         MOV     r0, #DisplayChanged_Changing
         MOV     r2, r5
         IssueService
-        CMP     r5, #GraphicsVInvalid
-        BLNE    InitialiseMode
+        BL      InitialiseMode
+        MOVVS   lr, #255
+        STRVSB  lr, [WsPtr, #ScreenBlankDPMSState]
         ; TODO - Try harder if this 2nd call fails (e.g. try all drivers in turn)
         MOV     r0, #DisplayChanged_Changed
         IssueService
         MOV     r1, r5
         SETV
         EXIT
+
+15
+        ; Success!
+        MOV     r0, #DisplayChanged_Changed
+        IssueService
+        MOV     r1, r5
+        EXIT
 20
         PullEnv
         ADR     r0, ErrorBlock_BadGDriver