English Amiga Board - View Single Post - 68030 write-allocate mode

TheDarkCoder · 13 August 2011, 19:35

Hi,

during my holydays I am enjoying a refresch of my knowledge about computer architechtures. While reading about caches, maybe stimulated by the recent Photon statement about poking every bit and byte of the Amiga, I recalled the following.
The 68030 has a "write-allocate" mode (writes in memory cause the written to location to be put in cache). In the ninethies, I tried to activate such a mode and found out that the Amiga did not worked as expected. In particular a blitter-rendered 3D scene was not correctly rendered. I don't remmber exactly the errors, but the rendered image has small but noticable missing pixels. The tests were done on a A4000 with a C= 3630 (030 25Mhz) CPU card.
I think that at that time I also discovered some official C= note saying that the 68030 write-allocate mode was not compatible with the way Amiga bus works.
I apologize for not recalling more details, but basically that was what I know about the subject.

I would like to know a more detailed reason for the impossibility to use this mode on the Amiga, and I wonder if any of the many hardware/low-level gurus in this forum can help.

13 August 2011, 19:35	#1
TheDarkCoder Registered User Join Date: Dec 2007 Location: Dark Kingdom Posts: 213	68030 write-allocate mode Hi, during my holydays I am enjoying a refresch of my knowledge about computer architechtures. While reading about caches, maybe stimulated by the recent Photon statement about poking every bit and byte of the Amiga, I recalled the following. The 68030 has a "write-allocate" mode (writes in memory cause the written to location to be put in cache). In the ninethies, I tried to activate such a mode and found out that the Amiga did not worked as expected. In particular a blitter-rendered 3D scene was not correctly rendered. I don't remmber exactly the errors, but the rendered image has small but noticable missing pixels. The tests were done on a A4000 with a C= 3630 (030 25Mhz) CPU card. I think that at that time I also discovered some official C= note saying that the 68030 write-allocate mode was not compatible with the way Amiga bus works. I apologize for not recalling more details, but basically that was what I know about the subject. I would like to know a more detailed reason for the impossibility to use this mode on the Amiga, and I wonder if any of the many hardware/low-level gurus in this forum can help.