- Yes, my minimig AGA core was written pretty fast, the majority in a week of sick leave actually
You'd be surprised how little changes AGA requires on top of ECS. It is of course based on minimig ECS, which thanks to everyone working on it, especially yaqube, is a great place to start
There is also the AGA guide document, which describes all the added / changed custom registers of the AGA chipset. You can implement around 75% of AGA on top of ECS and still be completely ECS compatible, which makes testing it (With small ASM-one few-liner programs) very easy. Of course, once you switch Lisa ID, all hell breaks loose
Here is the approximate sequence how I did it:
* convert the minimig core to a single 28MHz clock (not absolutely neccessary, but I didn't know that at the time)
* check if SDRAM controller implementation is good enough for 64-bit DMA fetches (it was) and add 64bit data paths for sprite and bitplane data
* implement AGA color LUTs, converting the LUT to blockrams, fix HAM6, HAM8 & EHB modes
* implement dither for video output, as the MIST only supports 18-bit output
* implement new bitplane DMA sequencer, bitplane modulos etc - I spent most of the time on this
* add / fix 64-bit serializer regs for bitplane data and fix sprite serializer implementation
* than you can start incrementally adding bits from new AGA registers and testing as you go, like border sprites, color table XOR, color table offsets, ...
* keep in mind that the most complex parts of the chipset - the blitter and copper - aren't changed AT ALL!