Table of Contents
Isabel: SAGA Video Core
Overview
The SAGA Core contains the Isabel Core, which is a hugely improved version of the graphics chipset (AGA) that was used in classic Amigas.
Isabel provides both chunky and planar (native) screen modes.
Features
- Chunky plane that can be displayed on its own by any dedicated RTG driver.
- Supported resolutions: Any valid mode from
320×200to1920×1080. - Supported color depths:
8,15,16,24,32bits. - Supported pixel formats:
CLUT8,RGB15,RGB16,RGB24,RGB32,YUV422. - Hardware-accelerated video playback.
- Picture-in-picture support, for embedding a virtual screen in a window.
- Fast Akiko C2P routines.
- FrameBuffer can be any address from accessible FastRAM.
- FrameBuffer can be Read and Write, for Direct Hardware drawings.
- Ability to turn on scanlines in certain modes.
Planar (Native) Graphics
- Support for all original AGA modes.
- New enhanced mode with 10 planes.
- Two of those planes can be switched to chunky mode.
- All planes are controllable by Copper.
- Both little-endian and big-endian representations are allowed.
- Support for all original AGA “hardware sprite” features.
- New enhanced “hardware sprite” features.
- 16 sprite DMA channels are available.
- Sprites can be up to 32 pixels wide.
- Each sprite can have 16 colors, with its own, independent palette.
- Collision detection is done for each sprite pair separately.
- Thanks to sprite indirection, you can change a sprite's data extremely fast, just by changing a pointer instead of copying a whole memory region.
- Support for all original AGA Copper features.
- New enhanced Copper features.
- You can perform a 32-bit move with a single instruction, which doubles the speed.
- Third playfield.
- Support for up to 12 MB of ChipRAM.
- Fast screen updates due to accessing ChipRAM at FastRAM speeds.
- High memory bandwidth thanks to 128-bit DMA.
- Fast Blitter operations.
- Immediate Blitter for better backward-compatibility.
- Support for Atari planar modes.
Chunky VIDEO registers
The FrameBuffer of the Chunky Video Mode can be any address from accessible FastRAM, by specifying the SAGA_VIDEO_PLANEPTR register. The FrameBuffer is Readable and Writable, for faster Direct Hardware drawings.
| Register | Name | Access | Size | Description |
|---|---|---|---|---|
| DFF1EC | saga_video_planeptr | W | ULONG | Set the SAGA Video FrameBuffer Address |
| DFF1F4 | saga_video_mode | W | UWORD | Set the SAGA Video Mode |
The Chunky Video mode can accept virtually any resolution from 320×200 (LowRes) to 1920×1080 (1080p).
The video engine can be dynamically reconfigured at any time by filling a valid ModeLine.
| Register | Name | Access | Size | Description |
|---|---|---|---|---|
| DFF1F8 | saga_video_pllw | W | UWORD | Set the SAGA ModeLine PIXELCLOCK |
| DFF1FA | saga_video_pllr | R | UWORD | Set the SAGA ModeLine PIXELCLOCK |
| DFF300 | saga_video_hpixel | W | UWORD | Set the SAGA ModeLine HPIXEL |
| DFF302 | saga_video_hsstrt | W | UWORD | Set the SAGA ModeLine HSSTRT |
| DFF304 | saga_video_hsstop | W | UWORD | Set the SAGA ModeLine HSSTOP |
| DFF306 | saga_video_htotal | W | UWORD | Set the SAGA ModeLine HTOTAL |
| DFF308 | saga_video_vpixel | W | UWORD | Set the SAGA ModeLine VPIXEL |
| DFF30A | saga_video_vsstrt | W | UWORD | Set the SAGA ModeLine VSSTRT |
| DFF30C | saga_video_vsstop | W | UWORD | Set the SAGA ModeLine VSSTOP |
| DFF30E | saga_video_vtotal | W | UWORD | Set the SAGA ModeLine VTOTAL |
| DFF310 | saga_video_hvsync | W | UWORD | Set the SAGA ModeLine HVSYNC |
When the SAGA_VIDEO_MODE is set to SAGA_VIDEO_FORMAT_CLUT8, a palette should be defined by filling the 256-color lookup table. Each color is 32-bits long, in the ARGB format.
| Register | Name | Access | Size | Description |
|---|---|---|---|---|
| DFF400 | saga_video_clut [0] | W | ULONG | Set the SAGA CLUT8 Color #001 |
| DFF7FC | saga_video_clut [255] | W | ULONG | Set the SAGA CLUT8 Color #256 |
Chunky ModeLine description
Universal ModeLine Calculator (UMC for AmigaOS 3.x, available on Aminet) can be used to generate a valid ModeLine for a given resolution. For example, we can ask UMC for a valid ModeLine for a 800×600@60Hz resolution. Just type the following line (add the --rbt option for a reduced framebuffer):
Example of a standard ModeLine:
> umc 800 600 60
"MODENAME" PIXELCLOCK HPIXEL HSSTRT HSSTOP HTOTAL VPIXEL VSSTRT VSSTOP VTOTAL HVSYNC Modeline "800x600@60" 38.400000 800 832 912 1024 600 604 608 625 -HSync +VSync
Example of a reduced ModeLine:
> umc 800 600 60 --rbt
"MODENAME" PIXELCLOCK HPIXEL HSSTRT HSSTOP HTOTAL VPIXEL VSSTRT VSSTOP VTOTAL HVSYNC Modeline "800x600@60R" 35.500000 800 848 880 960 600 603 607 618 -HSync +VSync
ModeLine values description:
| Attribute | Short | Description |
|---|---|---|
PIXELCLOCK | Bandwidth (MHz) | How many dots it can output per second. |
HPIXEL | Width | Number of horizontal pixels drawn to the visible part of the screen. |
HSSTRT-HPIXEL | Front Porch | Amount of black pixels drawn to the right of the screen. |
HSSTOP-HSSTRT | Sync Pulse | Amount of time it takes to start another line. |
HTOTAL-HSSTOP | Back Porch | Amount of black pixels drawn to the left of the screen. |
VPIXEL | Height | Number of vertical pixels drawn to the visible part of the screen. |
VSSTRT-VPIXEL | Front Porch | Amount of black pixels drawn on the bottom of the screen. |
VSSTOP-VSSTRT | Vertical Sync | Amount of time it takes to move back up to the first line of the screen. |
VTOTAL-VSSTOP | Back Porch | Amount of black pixels drawn to the top of the screen. |
HVSYNC | Flags | Sync Polarity. HSync on High Byte, VSync on Low Byte. |
