GitLab

ControlList_Interlaced is taken to have meant "output interlaced sync on H/V" and "configure DMA to show alternate lines in the framestore on alternate fields", therefore SyncPol flags mean:
b43
 00 = 'normal' progressive scan
 01 = interlaced sync, but both fields show the same image
 10 = (invalid)
 11 = interlaced sync, fields use alternate lines from the image

Version 6.21. Tagged as 'Kernel-6_21'

Detail:
  Over the years the OS's substitute screen mode selection logic has grown to be a tangled mess, and the logic it does implement isn't always very useful. Additionally, the kernel is structured in such a way that it can be hard for modules to override it.
  This set of changes aims to fix the many of the problems, by doing the following:
  - Moving all substitute mode selection logic out of the core VDU driver code and into a Service_ModeTranslation handler. This means you now only have one place in the kernel to look instead of several, and modules can override the behaviour by claiming/blocking the service call as appropriate.
  - Moving handling of the built-in VIDC lists out of the core VDU driver code and into a Service_ModeExtension handler. This means programs can now inspect these VIDC lists by issuing the right service call (although you are essentially limited to lists which the GraphicsV driver is OK with)
  - Moving *TV interlace & offset adjustment logic into the Service_ModeExtension handler, since they're legacy things which can be handled more cleanly for MDF/EDID (and the old code was poking memory the kernel didn't own)
  - Adding a Service_EnumerateScreenModes implementation, so that if you end up in the desktop with ScreenModes non-functional, the display manager at least has something useful to show you
  - Enhancing the handling of the built-in numbered modes so that they are now available in any colour depth; the Service_ModeExtension handler (and related handlers) treat the builtin VIDC lists as a set of mode timings, not a discrete set of modes
  - Substitute mode selection logic is a complete re-write. Instead of trying a handful of numbered fallback modes, it now tries:
    - Same mode but at higher colour depths
    - Same mode but at lower colour depths
    - Alternate resolutions (half-width mode with no double-pixel if original request was for double-pixel, and default resolution for monitor type)
  - Combined with the logic to allow the builtin VIDC lists to be used at any colour depth, this means that the kernel should now be able to find substitute modes for machines which lack support for <=8bpp modes (e.g. OMAP5)
  - Additionally the mode substitution code will attempt to retain as many properties of the originally requested mode as possible (eigen values, gap mode type, etc.)
  Other improvements:
  - The kernel now actually vets the builtin VIDC lists instead of assuming that they'll work (which also means they'll have the correct ExtraBytes value, where applicable)
  - The kernel now uses GraphicsV 19 (VetMode2) to vet the mode during the mode switch process, using the result to detect where the framebuffer will be placed. This allows for GraphicsV drivers to switch between DA 2 and external framestores on a per-mode basis.
  - The kernel now supports mode selectors which specify LineLength values which are larger than necessary; this will get translated to a suitable ExtraBytes control list item (+ combined with whatever padding the driver indicates is necessary via the VetMode2 result)
  File changes:
  - hdr/KernelWS - Reserve space for a VIDC list, since the Service_ModeExtension implementation typically can't use the built-in list as-is
  - s/Arthur3 - Issue Service_ModeFileChanged when the configured monitor type is changed, so that DisplayManager + friends are aware that the set of available modes has changed
  - s/GetAll - Fiddle with GETs a bit
  - s/MemMap2 - Extra LTORG
  - s/NewIRQs - Small routine to install/uninstall false VSync routine (previously from PushModeInfo, which wasn't really the appropriate place for it)
  - s/Utility - Hook up the extra service call handlers
  - s/vdu/legacymodes - New file containing the new service call implementations, and some related code
  - s/vdu/vdudecl - Move mode workspace definition here, from vdumodes
  - s/vdu/vdudriver - Remove assorted bits of mode substitution code. Plug in new bits for calling GraphicsV 19 during mode set, and deal with ExtraBytes/LineLength during PushModeInfo
  - s/vdu/vdumodes - Move some workspace definitions to s/vdu/vdudecl. Tweak how the builtin VIDC lists are stored.
  - s/vdu/vduswis - Rip out more mode substitution code. Issue Service_ModeFileChanged when monitor type is changed by OS_ScreenMode.
Admin:
  Tested on Raspberry Pi 3, Iyonix, IGEPv5


Version 6.14. Tagged as 'Kernel-6_14'

Detail:
  ECFIndex and PalIndex claim to be mode variables, but it's impossible for extension modes to specify their values.
  Since they're easy to calculate from the ModeFlags and Log2BPP values, drop them from the mode workspace (+ table of builtin modes) and calculate them on the fly instead.
  File changes:
  - hdr/KernelWS - Drop ECFIndex & PalIndex from workspace
  - s/vdu/vdumodes - Adjust workspace definition, drop ECFIndex & PalIndex values from VWSTAB
  - s/vdu/vdudriver - Remove now-redundant copy loop from ModeChangeSub. Remove code from GenerateModeSelectorVars that sets up the ECFIndex & PalIndex values on the stack
  - s/vdu/vdugrafl - Adjust copy loop in SwitchOutputToSprite/Mask
  - s/vdu/vdupalette, s/vdu/vdupalxx - Add GetPalIndex routine to generate PalIndex on the fly. Drop the obsolete 16bpp palette/gamma table and shuffle the other entries to simplify GetPalIndex a bit.
  - s/vdu/vduplot - Add GetECFIndex routine to generate ECFIndex on the fly. Also, fix things so that mode 0 isn't the only rectangular-pixel mode which uses the special rectangular-pixel ECF patterns (index 0 vs. index 4). Fiddle with ExportedHLine a bit to avoid an out-of-range ADR.
  - s/NewReset - Fix UAL warning for MOV R0, AppSpaceStart. Adjust memset to not assume 512KB is the correct amount
Admin:
  Tested on Raspberry Pi 3


Version 6.11. Tagged as 'Kernel-6_11'

Detail:
  s/vdu/vdudriver, s/vdu/vdumodes - Re-introduce TTX256 so that 8bpp teletext will be used if no MDF is loaded
  s/vdu/vdudriver - If the video driver didn't support the native mode 7 colour depth, ModePromoTable was swapping it for another mode number, preventing the AltTTX code in FindOKMode from operating. So, skip the ModePromoTable check for mode 7.
  s/vdu/vduswis - Minor correction to alternate teletext mode search; 1<<5 = 32bpp, so stop search at log2bpp of 6
Admin:
  Tested on Raspberry Pi


Version 5.74. Retagged as 'Kernel-5_74'

Detail:
  This set of changes:
  * Adds support for the T, TX and TY mode string elements (as per RISCOS Ltd)
  * Adds support for entering arbitrary-resolution teletext modes by using mode selector blocks with the Teletext mode flag set
  * ScrRCol and ScrBRow mode variables can be provided in the mode selector in order to restrict the number of text rows/columns in teletext modes (as per RISCOS Ltd)
  * If the rows / columns are restricted in this manner then the text window will be centered on the screen, to try and avoid things looking too ugly (no variable text scaling implemented)
  * For HiResTTX, all colour depths >= 4bpp are now supported by teletext. This essentially makes the TTX256 switch obsolete.
  * If the "native" mode 7 is unavailable then the kernel will try a series of fallback resolutions & colour depths in an effort to find a combination that works
  Known bugs/issues:
  * Teletext column count has a max limit of 255 due to TTXDoubleCounts being a byte array
  * If there's a border around the text window, the border will not be refreshed when changing transparency modes using a VDU 23,18,0 sequence
  * ScreenLoad looks like it can overflow the LargeCommon buffer (no buffer size check) - needs fixing before LargeCommon can be safely shrunk below (Old)TTXMapSize
  File changes:
  - hdr/KernelWS - Make CharWidth non-conditional. Adjust handling of teletext workspace; it's now allocated from the system heap to allow it to cope with arbitrary screen sizes
  - s/vdu/vdu23 - Make CharWidth non-conditional
  - s/vdu/vducursoft - Make CursorTeletext cope with arbitrary colour depths, make CharWidth non-conditional, remove hard-coded teletext values
  - s/vdu/vdudriver - Deal with teletext workspace allocation during ModeChangeSub. Deal with selecting teletext modes (and validating colour depth) in GenerateModeSelectorVars.
  - s/vdu/vdugrafl - Make CharWidth non-conditional. Calculate offset required for text window centering.
  - s/vdu/vdumodes - Remove TTX256
  - s/vdu/vduswis - Try other teletext modes if native mode 7 not available. Extend OS_ScreenMode reason codes to cope with teletext mode strings.
  - s/vdu/vduttx - Update to use dynamic workspace. Replace various hardcoded values with variable lookups. Update character plotting + colour/palette selection to work with true-colour modes if HiResTTX.
  - s/vdu/vduwrch - Move some useful code into a subroutine. Update FastCLS to cope with true-colour teletext. Update AddressR0R1 to cope with text window centering offset. Make CharWidth non-conditional.
Admin:
  Tested on Raspberry Pi, BB-xM
  VDU 23,18,0 in 256-colour teletext now works correctly (previously 64-colour mode was in use, causing palette update to be ruined by VIDC1-mangling)


Version 5.74. Tagged as 'Kernel-5_74'

Detail:
  This change gets rid of the following switches from the source (picking appropriate code paths for a 32bit HAL build):
  * FixCallBacks
  * UseProcessTransfer
  * CanLiveOnROMCard
  * BleedinDaveBell
  * NewStyleEcfs
  * DoVdu23_0_12
  * LCDPowerCtrl
  * HostVdu
  * Print
  * EmulatorSupport
  * TubeInfo
  * AddTubeBashers
  * TubeChar, TubeString, TubeDumpNoStack, TubeNewlNoStack macros
  * FIQDebug
  * VCOstartfix
  * AssemblingArthur (n.b. still defined for safety with anything in Hdr: which uses it, but not used explicitly by the kernel)
  * MouseBufferFix
  * LCDInvert
  * LCDSupport
  * DoInitialiseMode
  * Interruptible32bitModes
  * MouseBufferManager
  * StrongARM (new CacheCleanerHack and InterruptDelay switches added to hdr/Options to cover some functionality that StrongARM previously covered)
  * SAcleanflushbroken
  * StrongARM_POST
  * IrqsInClaimRelease
  * CheckProtectionLink
  * GSWorkspaceInKernelBuffers
  * EarlierReentrancyInDAShrink
  * LongCommandLines
  * ECC
  * NoSPSRcorruption
  * RMTidyDoesNowt
  * RogerEXEY
  * StorkPowerSave
  * DebugForcedReset
  * AssembleKEYV
  * AssemblePointerV
  * ProcessorVectors
  * Keyboard_Type
  Assorted old files have also been deleted.
Admin:
  Identical binary to previous revision for IOMD & Raspberry Pi builds


Version 5.51. Tagged as 'Kernel-5_51'

Detail:
  s/vdu/vdumodes - Redefine VgaX_7 to be VLM_7 if HiResTTX/TTX256 in use
Admin:
  Tested on Raspberry Pi
  Fixes nasty crash when selecting mode 7 without an MDF loaded due to VIDC list being mismatched with code/VWSTAB


Version 5.35, 4.79.2.219. Tagged as 'Kernel-5_35-4_79_2_219'

Detail:
  hdr/Options, s/ArthurSWIs, s/ChangeDyn, s/PMF/KbdDrA1, s/PMF/key, s/vdu/vdugrafa, s/vdu/vdugrafd, s/vdu/vdugrafhal, s/vdu/vdugrafv, s/vdu/vdumodes, s/vdu/vduwrch:
  - Strip out DoingVdu build switch (did nothing)
  - Strip out Japanese16BitSound switch (did nothing)
  - Strip out MakeModeSelectorsForModeNUmbers switch (altered the mode list structures, but there wasn't any code to do anything with the new data)
  - Strip out remaining uses of UseGraphicsV switch (now hardwired to {TRUE})
  - Strip out ShadowROM switch (altered FixedAreasTable to show the shadow mapping, but code to create the mapping is missing)
  - Strip out PollMouse switch (old Archimedes-era debug/development option)
Admin:
  Tested on BB-xM
  Builds to same binary as previous version


Version 5.35, 4.79.2.204. Tagged as 'Kernel-5_35-4_79_2_204'

Detail:
  This set of changes:
  * Adds basic support for multiple GraphicsV drivers, by way of some new OS_ScreenMode reason codes for registering/deregistering, selecting and enumerating drivers (11, 64-68)
  * Tidies up handling of HAL video calls so that the HAL calls will be transformed into a bona fide GraphicsV driver if they're implemented
  * Changes handling of 16bpp gamma table entries so that they're sent to GraphicsV in a generic form instead of in a VIDC-specific form
  * Adds a new GraphicsV call and defines new VIDC list items to allow GraphicsV drivers to utilise the new pixel formats
  File changes:
  * h/VIDCList, hdr/VIDCList, Makefile - Add new header export containing VIDC list type 3 definitions, to avoid repeated definitions in other components
  * Resources/UK/Messages - Add new GraphicsV/OS_ScreenMode error strings and some missing processor type strings
  * hdr/KernelWS - Clean up some pre-GraphicsV definitions, and add new workspace locations for storing the current GraphicsV driver number and the driver list
  * hdr/Options - Remove obsolete InverseTextTransparency option
  * hdr/VduExt - Add VDU variable 192 for storing GraphicsV driver number (same as ROL's VideoV driver number). Remove old 'Flag_*' mode flag definitions (use new 'ModeFlag_*' defintions instead). Add new OS_ScreenMode reason codes.
  * s/ARM600, s/VMSAv6, s/vdu/vdu23, s/vdu/vdugrafa, s/vdu/vdugrafd, s/vdu/vdupalxx, s/vdu/vdupointer, s/vdu/vduwrch - Strip out pre-GraphicsV code. Update GraphicsV code to use correct driver number.
  * s/ArthurSWIs - Pass the default GraphicsV claimant the VduDriverWorkSpace instead of ZeroPage
  * s/Getall - Add Hdr:VIDCList and s/vdu/VduGrafHAL to list of GETs
  * s/NewIRQs - Remove HAL VSync IRQ initialisation, is now handled by grafvhal. Remove old HAL VsyncIRQ entry point, all VSyncs are now handled by VsyncIRQ_ExtEntry.
  * s/PMF/osbyte - Stop OS_Byte 19 waiting forever if no video driver is active
  * s/PMF/osinit - Remove HAL VSync IRQ initialisation, is now handled by grafvhal
  * s/vdu/vducursoft - Use new workspace variable names and flag names
  * s/vdu/vdudecl - Remove old HALDAG_* definitions, GVDAG_* definitions are used instead. Add definition of the per-driver workspace structure and flags.
  * s/vdu/vdudriver - Remove pre-GraphicsV code. Update InitialiseMode to check for and initialise a HAL driver. Use cached driver features word in a few places instead of calling GraphicsV each time. Update PalIndexTable to disable VIDC mangling of 16bpp gamma tables.
  * s/vdu/vdugrafv, s/vdu/vdugrafhal - HAL<->GraphicsV code split off into its own file (vdugrafhal). Default GraphicsV claimant now only deals with VSync events for the active driver.
  * s/vdu/vdumodes - Get rid of old VIDC List type 3 definiton; now in hdr/VIDCList
  * s/vdu/vduswis - Added OS_ScreenMode reason codes 11 and 64-68 for registering, deregistering, selecting and enumerating GraphicsV drivers. Update mode set code to not bother checking if the driver supports the pixel format; instead we assume that the driver's vet mode call will do the check for us.
Admin:
  Tested in Tungsten, IOMD, OMAP3 & BCM2835 ROMs
  Requires HdrSrc-2_38 and updated video driver modes


Version 5.35, 4.79.2.203. Tagged as 'Kernel-5_35-4_79_2_203'

Add support for the new RISC OS 5 style sprite mode word. Add partial support for alpha channel sprite masks. Implement OS_ScreenMode reasons 13-15

Detail:
  ECFShift/ECFYOffset:
  - hdr/PublicWS - Add ECFShift and ECFYOffset to list of public exports (SpriteExtend was using hardcoded values). Rearrange exports so that VduWorkspace exports are now labelled as such.
  - hdr/KernelWS - Make sure ECFShift & ECFYOffset match their exported locations
  - hdr/OSRSI6, s/Middle - Add OS_ReadSysInfo 6 items 83 & 84, for reading ECFYOffset and ECFShift locations
  Mode flags/VDU variables:
  - Makefile - Add hdr/VduExt to the C header exports
  - hdr/VduExt - Get rid of NotRVVTBarWobblyBits macro and defined VDU variables manually so that Hdr2H will handle them. Begin replacing overly generic 'Flag_*' mode flag definitions with 'ModeFlag_*' instead. Define new flags as required by the new screen/sprite modes. Add OS_ScreenMode reason codes and mode selector format (from s.vdu.vdudecl)
  - NewModes/NEWF2, NewModes/OldPSSrc, NewModes/PSSrc, s.vdu.vdu23, s.vdu.vducursoft, s.vdu.vdudriver, s.vdu.vdugrafg, s.vdu.vdugrafj, s.vdu.vdugrafl, s.vdu.vdumodes, s.vdu.vdupal10, s.vdu.vdupal20, s.vdu.vdupalette, s.vdu.vdupalxx, s.vdu.vduwrch - Renaming Flag_* to ModeFlag_*
  - s.vdu.vdudecl - Remove OS_ScreenMode reason codes & mode selector format definitions; these are now in hdr/VduExt. Flag_* -> ModeFlag_* renaming.
  - s.vdu.vdupalxx - Apply a greyscale palette in PV_SetDefaultPalette if the greyscale mode flag is set
  New sprite types:
  - s.vdu.vdudriver - Extend GenerateModeSelectorVars to deal with the wide mask flag, 64K sprites, and the new RISC OS 5 sprite mode word format.
  - s.vdu.vdugrafdec - Store more information about the sprite in the SprReadNColour ... SprLog2BPC block.
  - s.vdu.vdugrafg - Update SpriteVecHandler to be able to detect whether RISC OS 5 format sprites are allowed palettes. Update SetupSprModeData to store the extra sprite info that's defined in vdugrafdec. Update PutSprite to fault any sprites with wide masks - SpriteExtend must be used for that (once implemented!)
  - s.vdu.vdugrafh - Update WritePixelColour to avoid temporary poking of NColour VDU variable for 8bpp sprites. Correctly replicate data when writing to RISC OS 5 format sprites. Update ReadPixelMask, WritePixelMask, SpriteMaskAddr, GetMaskspWidth to deal with wide masks. Delete obsolete bounce_new_format_masks routine.
  - s.vdu.vdugrafi - Comment updated to reflect new reality
  - s.vdu.vdugrafj - Get rid of unused code block in CreateHeader/PostCreateHeader. Update SanitizeSGetMode to generate RISC OS 5 style sprite mode words where applicable. Update DecideMaskSize to rely on GetMaskspWidth for calculating mask width.
  - s.vdu.vdugrafl - Update SwitchOutputToSprite/SwitchOutputToMask to deal with the new sprite formats. Allow PushModeInfoAnyMonitor to fail.
  - s.vdu.vduswis - Extended OS_ReadModeVariable to cope with new sprite types
  Misc:
  - s.vdu.vdudriver - Fixed bug with VIDCList copying where any -1 value in the structure would terminate the copy, instead of only -1 as a control item number
  - s.vdu.vduswis - Implemented OS_ScreenMode 13 (Mode string to specifier), 14 (mode specifier to string), and 15 (set mode by string). Mostly as per ROL's specs, but minus support for teletext attributes, and plus support for new RISC OS 5 attributes (L... layout specifier, 4096 & 24bpp packed modes, etc.)
  - s.vdu.vduwrch - Pick correct default text colours for the new modes
Admin:
  Tested on BB-xM
  Part of an implementation of the Extended Framebuffer Format spec:
  http://www.riscosopen.org/wiki/documentation/show/Extended%20Framebuffer%20Format%20Specification


Version 5.35, 4.79.2.194. Tagged as 'Kernel-5_35-4_79_2_194'

Detail:
  s/vdu/vdumodes - Mode 47 is 360 pixels wide, so should be 45 text columns, not 90
Admin:
  Tested in Iyonix ROM softload


Version 5.35, 4.79.2.140. Tagged as 'Kernel-5_35-4_79_2_140'

	no other changes
Detail:
Admin:


Version 5.35, 4.79.2.91. Tagged as 'Kernel-5_35-4_79_2_91'

  [Not fully implemented - for now leaves at least 16MB free if only
  one RAM area; was 1MB].
* Added HAL_USBControllerInfo, HAL_MonitorLeadID and HAL_Video_Render.
* Added HAL->OS call OS_IICOpV.
* OS_MMUControl now allows independent control of I and C bits.
* Added facility to deactivate keyboard debounce (magic word "NoKd" in
  R2 in KeyV 0).
* Fixed problem with RAM amounts not a multiple of 4MB.
* Supremacy bit (in VDU 19) now sets all 8 bits of supremacy.
* Added PaletteV 14 (reads gamma tables).
* Added Supremacy transfer functions (like gamma correction, but for
  supremacy). Allows easy global supremacy effects in a mode-independent
  fashion. Controlled with PaletteV 15,16.
* Added modes 50-53 (320x240, 1,2,4,8bpp). Intended for small LCD.
* Added 13.5kHz versions of TV modes (selected by Hdr:Machine).
* Upped desktop version to 5.06.

Version 5.35, 4.79.2.66. Tagged as 'Kernel-5_35-4_79_2_66'

Added 256-colour version of the (high-resolution only) teletext code, and support for teletext when hardware scroll is disabled. Both are required for Tungsten.

Turned off the module init/final service calls, since we still don't have an
allocation for them.
Upped the OS version number to 5.01.

Version 5.35, 4.79.2.53. Tagged as 'Kernel-5_35-4_79_2_53'

Version 5.35, 4.79.2.18. Tagged as 'Kernel-5_35-4_79_2_18'

More stuff. Up to the desktop now; cache on, working keyboard. Some source restructuring to start to make splitting it up into several object files more feasible.

partial video changes for kernel/HAL split near-HAL code for VIDC/IOMD in vdu.vduhint briefly tested in Ursula desktop build still some kernel workspace dependency in near-HAL code

Version 5.35, 4.79.2.3. Tagged as 'Kernel-5_35-4_79_2_3'

Added compile-time support for full-resolution teletext characters in teletext emulation mode (MODE 7) for that authentic BBC Micro feel.

  Also introduced a few useful teletext control features via VDU 23,18.
  Unrelatedly, fixed *ScreenLoad to work for interlaced displays.

Detail:
  The new typeface is designed on a 16x20 grid (previously we had used 8x10),
  so it uses a screen resolution of 640x500 pixels (rather than 320x250).
  Since we have been unable to source a genuine teletext font, and since
  examination of a BBC Micro suggests that the genuine font may not have been
  a power-of-2 pixels wide, I have designed one specially, based upon the one
  supplied in Zap distributions (a 12x20 font). Rather than increase the
  amount of workspace that the kernel requires for cacheing graphic
  characters, it now generates them on the fly, as they are required; this
  should only add about 25% to their rendering time.

  The new VDU 23 sequences are as follows:

  VDU 23,18,0,mode,0,0,0,0,0,0
    Switch transparency mode
      mode = 0: "Text" mode: the whole display is set opaque
      mode = 1: "Mix" mode: foreground colours, and both foreground and
        background of boxed text are opaque; non-boxed background colours are
        all transparent
      mode = 2: "Box" mode: boxed regions are opaque, others are transparent
      mode = 3: "TV" mode: the whole display is set transparent
    Default is mode = 0.

  VDU 23,18,1,suspend,0,0,0,0,0,0
    Suspend or resume bitmap updates
    This call allows an application to request that the kernel suspends
    updates to the framebuffer bitmap. This allows for a significant speed
    increase in the rendering time for a large amount of text, for example
    when redrawing a complete teletext page, because each time you plot a
    single character, it can cause the whole of the rest of the line to be
    re-rendered. When you switch out of suspend mode, the whole screen is
    refreshed in a single pass. Note that the appearance of the display is
    undefined is you cause a hardware scroll while in suspend mode.
      suspend = 0: screen update is enabled
      suspend = 1: screen update is suspended
    Default is suspend = 0.

  VDU 23,18,2,reveal,0,0,0,0,0,0
    Reveal/conceal
      reveal = 0: characters between the Conceal control code and the next
        colour control code are replaced by spaces
      reveal = 1: all characters are displayed
    Default is reveal = 0.

  VDU 23,18,3,black_emable,0,0,0,0,0,0
    Enable/disable black foreground colour control codes
      black_enable = 0: control codes &80 and &90 do nothing
      black_enable = 1: control code &80 selects black text, control code
        &90 selects black graphics
    Default is black_enable = 0.

  I have performed some timing tests on the rendering of complete teletext
  pages grabbed from the teletext server. These show that the new code
  generally imposes a 2x speed hit. However, when using the VDU 23,18,1
  suspend function, this improves to a 20% speed increase when compared to
  the old low-resolution code. Better still, because the framebuffer is only
  being updated for the final stage of this process, the screen *appears* to
  be updated some 3x faster than with the old code!

  A comment on the VDU variable Log2BPC is in order: in previous kernels,
  this was able unambiguously to refer to both the framebuffer width of a
  character in bytes, and the framebuffer width of an "addressable pixel" in
  bits; this no longer works with the 16-pixel wide teletext font. Bearing
  in mind that future kernels may support Unicode system fonts where the
  width varies from character to character, I have chosen to fix Log2BPC to
  the "addressable pixel" definition.

Admin:
  Requires HdrSrc 0.89 and (for non-desktop builds) Interlace 0.61. A monitor
  definition file containing a definition for a 640x500 screen mode is also
  required; version 0.40 of ModeFiles contains a suitable mode for STB-400.

  Tested fairly rigourously on an Ursula build, a Lazarus build and an
  STB-400 build, using genuine teletext pages and Yellow River Kingdom.

Version 5.30. Tagged as 'Kernel-5_30'

* Wasn't allowing writes to most of EEPROM.
* Old prototype OS_SetTime SWI code removed.
* MPEGPoduleNTSCNotPALMask option support removed to simplify things a bit.
* Now can cope with a system with a PAL/NTSC link, but no monitor detect line.
* Default PAL & NTSC modes now always 12 & 46 respectively.
* Kernel now knows about monitor type 8 (NTSC) - modes 44-46 (640x200) are
  available.
* STB/NC CMOS test removed from POST pending further investigation.

Version 4.90. Tagged as 'Kernel-4_90'

Bandwidth limit for 7500FE fixed.
RO371Timings flag set to :LNOT:STB

Version 4.64. Tagged as 'Kernel-4_64'