| From: | David McMinn |
| Date: | 24 Aug 2001 at 12:35:02 |
| Subject: | Re: initdisplay |
Hi BenJDvs@aol.com
> I`m having trouble with creating displays using the display library
> commands. The trouble is with the flags field of the initdisplay command.
> I`m using #8bitplanes #smoothscrolling #dualplayfield #hires and
> #agacolours, but I don`t know which fetchmode value to use. What exactly
> does it mean and how will it affect the display?
The fetchmode was something introduced with the AGA chipset IIRC (or
perhaps ECS). It changes the way data is accessed by the custom chips.
Fetchmode 0 (the default, and the one in the OCS) accesses everything in
sets of 2 bytes. Fetchmode 1 and 2 access things in blocks of 4 bytes,
although there's a slight difference between the way they work. Fetchmode
3 accesses everything in blocks of 8 bytes.
It should not affect the display too much if you do everything via the
display library - all fetchmode calculations are taken care of by it.
The higher the fetchmode, the more bandwidth is given to the custom
chips, so you'd want to use as high a fetchmode as possible. For example,
with fetchmode 0, you'd need to use a narrow display with all 8 sprites
enabled, but you'd get the full display with using fetchmode 3. I think.
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