[openbeos] Re: ARM port

On Jun 29, 2008, at 10:52 AM, François Revol wrote:


The boards I'm looking at to use are based on the Cortex A8, it is 2
generations newer, that said I'll have to look into the differences
between V6 (ARM 11) and V7 (A8+) so it doesn't rule out the ARM11.
I already added the needed stuff to binutils, might look into gcc but I 
have stuff to prepare for RMLL.

OTH I could arrange a workshop on porting Haiku to ARM there :D

I suggest you see how uboot works, didn't look much myself yet.
The biggest difference in the v7 stuff for os supporting is the different cache architecture. ARM changed the cache control bits again for the cortex, and now it's somewhat more complicated, but it should be documented if you have the arm v7 docs. Seeing as Nicholas works for ARM he should be able to get ahold of it legitimately. Other than that, it's for the most part just the same as v6. Thankfully the cache is now fully physically coherent, so none of that cache flushing mess that you have to do on earlier arms, and some of the v6s.
Fully supporting thumb2 + neon + lazy fpu save is a bit more of a challenge as well, since the kernel has to have enough knowledge to decode the instructions and differentiate between a real bad instruction and just a disabled fpu instruction.
One area that haiku may bump into trouble is the general lack of support for systems with dma incoherent devices. Most oses have some sort of knowledge of this, and let you allocate regions with cache disabled and whatnot to make it easier to sync with dma that happens in the background. Without it you'll probably have to overly flush the cache in the low level drivers and there still may be some cache line aliasing issues. Shouldn't be too bad, since most of the drivers would need to be custom to the board anyway. 

travis

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