While the CPU is still not as stable as I’d like, the latest bitfield fixes by Till Harbaum fixed a lot of games and demos that didn’t work properly before. To show the differences, here are some examples, showing the same picture, on the left we have HAM6 (4096 colours) and EHB (64 colours), on the right we have HAM8 (262144 colours) and 256 colours.There is a new release of minimig-AGA for the MiST board available, grab it on the minimig-mist page! It also allowed output in higher resolutions for the higher colour modes, so you could have a 640×400 screen showing 256 colours, or even showing HAM8 and it’s 262,144 possible colours. This meant that operations done by the custom chips were up to 4 times the speed when compared to the previous generations, which is a considerable improvement. The bus width for the Chip RAM access to and from the custom Chips was doubled, from 16-bit to 32-bit, to allow more to be completed on each bus cycle. However, it is still capable of showing some absolutely stunning pictures that are visually very close to a modern true colour picture. This increased the maximum onscreen colours without using tricks to 256 colours, and added a new HAM mode, HAM8, which can technically show virtually all of the over 16 million colours available in the palette, but due to the restriction in how HAM8 mode operates, using a base palette of 64 colours and then modifying the Red, Green or Blue of the pixel to the right, realistically you can’t use all the available colours in a useful way. In AGA, this was doubled to 8 bits for each RGB element, giving a total of a 16.8 million colour palette (256*256*256=16,777,216 colours) while retaining near total compatibility with older software. HAM could show all possible colours, with restrictions, and EHB could display 64 colours, but both had heavy restrictions, and are covered in more detail on the pages for OCS and ECS. In the previous OCS and ECS chipsets, the colour palette was always formed using 4bits for each of the Red, Blue and Green elements, giving a total of 4096 colours (16*16*16=4096) to choose from, of which 32 could be shown onscreen at once without using the EHB or HAM6 video modes. It was originally going to be called the AA chipset, but it was changed to AGA, which apparently stood for “Advanced Graphics Architecture”, which sounds about right, because while the graphic output had quite a number of changes, the audio system was untouched. The final revision to the Amigas custom chips came to be known as the AGA chipset.
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