mirror of
https://github.com/alfishe/amiga-bootcamp.git
synced 2026-06-13 00:26:28 +00:00
docs(amiga): complete AmigaOS 3.1/3.2 developer reference — 172 files across 17 sections
Comprehensive technical documentation covering: - Hardware: OCS/ECS/AGA custom chip registers, Copper & Blitter deep dives - Boot sequence: cold boot through startup-sequence - Binary format: HUNK executable spec, relocation, debug info - Linking & ABI: .fd files, LVO tables, register calling conventions - Exec kernel: tasks, interrupts, memory, signals, semaphores - AmigaDOS: file I/O, FFS/OFS layout, CLI/Shell scripting - Graphics: planar bitmaps, Copper programming, HAM/EHB modes - Intuition: screens, windows, IDCMP, BOOPSI - Devices: trackdisk, SCSI, serial, timer, audio, keyboard - Libraries: utility, expansion, IFFParse, locale, ARexx - Networking: bsdsocket API, SANA-II, TCP/IP stack comparison - Toolchain: GCC, vasm/vlink, SAS/C, NDK, debugging - Reverse engineering: IDA/Ghidra setup, compiler fingerprints, case studies - CPU & MMU: 68040/060 emulation libs, PMMU, cache management - Driver development: SANA-II, Picasso96/RTG, AHI audio All files include breadcrumb navigation. No local paths or proprietary content.
This commit is contained in:
Ilia Sharin
parent
f07a368bf1
commit
21751c0025
172 changed files with 19701 additions and 0 deletions
167
01_hardware/aga_a1200_a4000/aga_blitter.md
Normal file
167
01_hardware/aga_a1200_a4000/aga_blitter.md
Normal file
|
|
@ -0,0 +1,167 @@
|
|||
[← Home](../../README.md) · [Hardware](../README.md) · [AGA](README.md)
|
||||
|
||||
# AGA Blitter — What It Is, What It Does, and 64-bit Bus Mode
|
||||
|
||||
## What Is the Blitter?
|
||||
|
||||
The **Blitter** (Block Image Transfer) is a dedicated DMA hardware engine inside every Amiga, designed to move and transform rectangular blocks of bitmap data **without CPU intervention**. While the CPU handles game logic, AI, physics, and sound setup, the Blitter does the heavy graphical lifting in the background.
|
||||
|
||||
Think of it as a **hardware GPU for 2D raster operations** — years before PC graphics cards existed.
|
||||
|
||||
### What the Blitter Can Do
|
||||
|
||||
| Capability | Description | Typical Use |
|
||||
|---|---|---|
|
||||
| **Block copy** | Move rectangular bitmap regions | Scrolling backgrounds, restoring screen areas |
|
||||
| **Cookie-cut blit** | Stamp a shape onto a background using a mask | Drawing game sprites (BOBs) with transparency |
|
||||
| **Area fill** | Fill arbitrary shapes | Flood-filling polygons, UI element backgrounds |
|
||||
| **Line drawing** | Draw lines using hardware Bresenham | Vector graphics, wireframe 3D |
|
||||
| **Clear/set memory** | Zero or fill large memory blocks | Screen clearing between frames |
|
||||
| **Logic operations** | Combine 3 inputs with any Boolean function | XOR cursors, shadow effects, masking |
|
||||
| **Shifting** | Shift source data 0–15 pixels | Sub-word-aligned sprite positioning |
|
||||
|
||||
### What the Blitter Cannot Do
|
||||
|
||||
| Limitation | Detail |
|
||||
|---|---|
|
||||
| No scaling | Cannot resize images — fixed 1:1 pixel mapping |
|
||||
| No rotation | Cannot rotate — must be pre-rendered in software |
|
||||
| No 3D | No perspective, texture mapping, or Z-buffer |
|
||||
| No chunky pixels | Operates on **planar** bitplanes only (1 plane at a time) |
|
||||
| No colour blending | Pure Boolean logic — no alpha, no transparency gradients |
|
||||
| Word-aligned width | Minimum operation width is 16 pixels (1 word) |
|
||||
|
||||
### How Software Uses It
|
||||
|
||||
**Games** — The blitter draws BOBs (Blitter Objects = software sprites) by cookie-cutting character graphics onto the playfield. A typical game frame:
|
||||
1. Blitter restores background behind old sprite positions
|
||||
2. Game logic updates positions
|
||||
3. Blitter draws sprites at new positions using cookie-cut
|
||||
4. Copper switches display to the newly drawn buffer (double-buffering)
|
||||
|
||||
**Demos** — Demoscene coders exploit every blitter trick: interleaved bitplane blits, fill-mode for filled vector polygons, line-mode for wireframes, and careful DMA scheduling to run blitter and CPU in parallel.
|
||||
|
||||
**Applications** — Workbench uses `BltBitMap()` for window dragging, scrolling text, and refreshing damaged screen areas. The `layers.library` damage repair system depends entirely on blitter operations.
|
||||
|
||||
---
|
||||
|
||||
## AGA Enhancements
|
||||
|
||||
AGA's Alice chip extends the blitter with a **64-bit data bus mode** controlled by the `FMODE` register. This allows the blitter to fetch 2 or 4 words per DMA cycle, dramatically increasing fill and copy throughput for large bitmap operations.
|
||||
|
||||
## FMODE Configuration
|
||||
|
||||
`FMODE` ($DFF1FC) controls blitter, bitplane, and sprite DMA fetch widths independently:
|
||||
|
||||
```
|
||||
bits 9-8: BLT_FMODE — blitter fetch mode
|
||||
00 = 16-bit (OCS compatible)
|
||||
01 = 32-bit
|
||||
10 = 64-bit
|
||||
11 = reserved
|
||||
|
||||
bits 13-12: BPL_FMODE — bitplane fetch mode (same encoding)
|
||||
bits 15-14: SPR_FMODE — sprite fetch mode (same encoding)
|
||||
```
|
||||
|
||||
Setting 64-bit blitter mode:
|
||||
```asm
|
||||
move.w #$0300, $DFF1FC ; BLT_FMODE = 10 (64-bit)
|
||||
```
|
||||
|
||||
> [!IMPORTANT]
|
||||
> FMODE must be set **before** loading blitter registers and starting the blit. Changing FMODE mid-blit causes undefined behaviour.
|
||||
|
||||
## Width Calculation with FMODE
|
||||
|
||||
When using wider fetch modes, **BLTSIZE widths must be adjusted**:
|
||||
|
||||
| FMODE | Width unit | Width formula |
|
||||
|---|---|---|
|
||||
| 1× (16-bit) | 1 word = 16 bits | `width_in_words` |
|
||||
| 2× (32-bit) | 2 words = 32 bits | `(width_in_words + 1) / 2` |
|
||||
| 4× (64-bit) | 4 words = 64 bits | `(width_in_words + 3) / 4` |
|
||||
|
||||
Example: blitting 320 pixels wide (20 words):
|
||||
- 1× mode: BLTSIZE width = 20
|
||||
- 2× mode: BLTSIZE width = 10
|
||||
- 4× mode: BLTSIZE width = 5
|
||||
|
||||
**Modulo values are still in bytes** regardless of FMODE.
|
||||
|
||||
## Performance Comparison
|
||||
|
||||
For a typical 320×200 blit (simple copy, 1 bitplane):
|
||||
|
||||
| Mode | FMODE | Approx time (7 MHz) |
|
||||
|---|---|---|
|
||||
| OCS/ECS | 1× | ~1.8 ms |
|
||||
| AGA 2× | 2× | ~0.9 ms |
|
||||
| AGA 4× | 4× | ~0.45 ms |
|
||||
|
||||
## Alignment Requirements
|
||||
|
||||
Wider fetch modes impose alignment constraints on source/destination pointers:
|
||||
|
||||
| FMODE | Required alignment |
|
||||
|---|---|
|
||||
| 1× | 2 bytes (word) |
|
||||
| 2× | 4 bytes (long) |
|
||||
| 4× | 8 bytes (quadword) |
|
||||
|
||||
Misaligned pointers with 2× or 4× FMODE produce incorrect blit results.
|
||||
|
||||
## Using graphics.library
|
||||
|
||||
The OS `BltBitMap()` / `BltBitMapRastPort()` calls are FMODE-aware in OS 3.1+ on AGA hardware:
|
||||
|
||||
```c
|
||||
BltBitMap(src_bm, srcx, srcy, dst_bm, dstx, dsty, width, height,
|
||||
0xC0, 0xFF, NULL); /* minterm $C0 = copy, all planes */
|
||||
```
|
||||
|
||||
`graphics.library` automatically selects the optimal FMODE for the current hardware.
|
||||
|
||||
## BLTCON0 / BLTCON1 — Unchanged in AGA
|
||||
|
||||
The minterm logic (`BLTCON0`) and fill/line mode (`BLTCON1`) registers are functionally identical to OCS/ECS. AGA only adds bandwidth, not new logical capabilities.
|
||||
|
||||
## Direct AGA Blitter Example (64-bit clear)
|
||||
|
||||
```asm
|
||||
; Clear 320×256 bitmap at address $100000 (20 words wide, 256 lines)
|
||||
; Using AGA 4× FMODE (5 quads wide)
|
||||
|
||||
move.w #$0300, $DFF1FC ; FMODE: BLT_FMODE = 4×
|
||||
|
||||
move.w #$0100, BLTCON0+custom ; USE D only, minterm $00 (fill with zero)
|
||||
move.w #$0000, BLTCON1+custom
|
||||
|
||||
move.w #$FFFF, BLTAFWM+custom ; first word mask
|
||||
move.w #$FFFF, BLTALWM+custom ; last word mask
|
||||
|
||||
move.l #$00100000, BLTDPTH+custom+$00 ; dest high word
|
||||
; (split into high/low)
|
||||
move.w #$0010, BLTDPTH+custom
|
||||
move.w #$0000, BLTDPTL+custom
|
||||
|
||||
move.w #0, BLTDMOD+custom ; modulo = 0 (contiguous)
|
||||
|
||||
; BLTSIZE = (256 lines << 6) | 5 quads width = (256*64)|5 = $4005
|
||||
move.w #((256<<6)|5), BLTSIZE+custom ; start blit
|
||||
|
||||
; wait for completion
|
||||
WaitBlit:
|
||||
btst #6, DMACONR+custom+1
|
||||
bne.s WaitBlit
|
||||
|
||||
; Restore FMODE to 1× for safety
|
||||
move.w #$0000, $DFF1FC
|
||||
```
|
||||
|
||||
## References
|
||||
|
||||
- ADCD 2.1 Hardware Manual — AGA blitter section
|
||||
- NDK39: `hardware/blit.h`, `hardware/custom.h`
|
||||
- Commodore A1200/A4000 Technical Reference Manuals — Alice section
|
||||
- graphics.library Autodocs: BltBitMap, BltClear
|
||||
Loading…
Add table
Add a link
Reference in a new issue