Minimig AGA
From Open Circuits
Obstacles to implementing the Amiga Advanced Graphics Architecture (AGA) on the Minimig Project (by alexh on 070726):
- The Minimig uses a MC68SEC000 which has only a 16 bit external address bus (No real point in AGA without an 020+), although Minimig Faster CPU with a wider bus is being considered.
- The Minimig uses 16-bit RAM (need 32-bit for AGA).
- The Minimig uses 12-bit R2R ladder / Video DAC (need 24-bit for AGA)
- You might be able to work around the RAM thing if you ran the RAM interface at 2x speed. (Dunno if that is possible, probably have to run everything at 2x speed and divide down inside FPGA). I guess you could ignore the lack of colours on the screen. (I've not looked that close at the PCB design, perhaps there are more than 12-bits, OCS/ECS only needs 12-bits but you never know.)
- But there is no getting round the CPU bit.
CPU prices from Digikey.com:
| Part | Description | Package | Price |
|---|---|---|---|
| MC68SEC000AA16 | 68000 @ 16 MHz | 64-QFP | $13.39 |
| MC68EC020AA16 | 68EC020 @ 16 MHz | 100-QFP | $21.10 |
| MC68EC040FE33A | 68EC040 @ 33 MHz | 184-CQFP | $132.88 |
Solutions:
- Put the 680x0 inside the FPGA due economics. The only non-BGA device with enough room for a 680x0 and the chipset is the Altera Cyclone III EP3C25.
- Use two Xilinx FPGAs with the largest package that can be had with "legs", ie PQ208 as per 070730 Xilinx Spartan-3 datasheet. One used for heavy tasks. Letting them share the tasks.
- Use Enterpoint/UK Xilinx FPGA XC3S1200 mounted on pcb with PGA socket. Costs 110 EUR (070730) and includes (usually) 16 MB SDRAM, 1.2V+2.4V onboard power.
24-bit video D/A prices:
| Part | Description | Package | Price |
|---|---|---|---|
| ADV7125KSTZ140 | 8-bit video DAC, 3 channels, 140 MHz | 48-LQFP | $10.15 |
| ADV7125KSTZ50 | 8-bit video DAC, 3 channels, 50 MHz | 48-LQFP | $9.65 |
Maybe RTG (ReTargetable Graphics) is interesting? (dault many games support it thoe).
- Apart from the graphics data fetches, AGA still operated on 16-bit data only, meaning that a lot of bandwidth was wasted during register accesses and copper and blitter http://en.wikipedia.org/wiki/Advanced_Graphics_Architecture
- Of course only AGA games/applications that used the 68EC020 as a 68000 would have any chances of working at all, at least that is how I undestand it.
