Re: [Tuxnes-devel] more help w/ asm

[Mike M. <mel...@pc...>]

On Wed, 11 Apr 2001, Jim Ursetto wrote:

> Hmmm... if translating assembly language between architectures is 
> not porting, then I don't know what is ;)

	Okay, you've got me there...:)

> More power to Rigel and I hope he succeeds.  While he's
> in there, it'd be great if he could look at some
> issues I noticed with dynrec:
[issues]

	Right. These are all well-known issues with the dyn-rec
approach. Basically, it doesn't cover all the bases with respect to
reading from and writing to the memory space. Naturally, this isn't a big
issue for 90% of the games out there, only the coolest 10%, such as
Castlevania III which uses MMC5 which maps its registers in the lower half
of memory.

	Also, don't forget another big problem with the dyn-rec
approach: It absolutely cannot handle self-modifying code. That's why it
also contains a translator that handles the most common instructions
empirically discovered in existing self-modifying routines.

> extremely uncommon.  Maybe we should consider
> contributing any interesting tidbits about the dynrec
> code to HACKING, or comment the code in especially
> difficult places.

	Since I do understand the dyn-rec engine to a decent extent (as
opposed to, say, the sound engine), I plan to document that well in the
HACKING file.

> All in all, the dynrec is incredibly cool, and it must
> have taken a huge effort to get it working and find all
> those special translation cases...  and it's very fast,
> nearly 10 times faster than the Nofrendo core, using
> the none renderer.

	10 times faster? Really? Finally, some real speed
comparisons. However, how much time does the program spend simulating the
6502 in comparison to, say, rendering the graphics 60 times per second?

> I implemented it this way in my copy of the tree,
> except dynrec/interpreted mode was a compile-time
> option.  It should be possible to do it on the fly,
> though.

	This is good. I'm thinking that we'll have to add another field to
the mapper table in order to indicate whether that mapper has to use the
portable core in order to work because it accesses lower memory. Whatever
the program chooses to use could be overridden by a run-time switch.

-- 
	-Mike Melanson