[B2-devel] [patch] Port SheepShaver's precise timer to OS X

[Charles S. <bas...@ch...>]

Attached is a set of patches to port the precise timer that is  
currently used in the Linux and BeOS builds of SheepShaver to Mac OS X  
(and any other Mach-based operating systems).

Currently, the Linux build uses the clock_gettime() function to get  
nanosecond-precision time, and falls back on gettimeofday() if it is  
not present. Unfortunately, Mac OS X does not currently support  
clock_gettime(), and gettimeofday() has only microsecond granularity.  
The Mach kernel, however, has a clock_get_time() function that does  
very nearly the same thing as clock_gettime(). The patches to  
BasiliskII cause the timing functions such as timer_current_time() to  
use clock_get_time() instead of gettimeofday() on Mach-based systems  
that do not support clock_gettime().

The changes to SheepShaver involve the precise timer. The existing  
code for Linux uses pthreads and real-time signals to handle the  
timing. Mac OS X unfortunately does not seem to support real-time  
signals, so Mach calls are again used to suspend and resume the timer  
thread in order to attempt to duplicate the Linux and BeOS versions of  
the timer. The code is somewhat ugly right now, as I decided to leave  
alone the pre-existing style of the source file, which unfortunately  
involves #ifdefs scattered throughout the file and some duplication of  
code. A future patch may want to clean this up to separate out the OS- 
specific code and put it all together at the top of the file. However,  
for the time being, this seems to work.

This has not been extensively tested, because I have not been able to  
get my hands on a good test-case app for the classic Mac OS that would  
run inside the emulator and try out the timer. However, performance  
does seem to be better than with the pre-existing code, and nothing  
seems to have blown up as far as I can tell. I did find a game via a  
Google search -  Cap'n Magneto - that is known to have problems with  
Basilisk/SheepShaver's legacy 60 Hz timer, and the opening fade-to- 
color for this game appears to run much more smoothly with the precise  
timer code in place.

I hope that you find these patches satisfactory.