Re: [avr-chat] Tenfold acceleration of Simulavr is possible.

[Erik Walthinsen]

Dmitry K. wrote:
> I have try to clean body of function `get_program_time'
> (src/utils.c) -- by `return 0'.

This makes sense, as gettimeofday() in libc is a kernel syscall.  A 
better, but more arch-specific method, would be to use the RDTSC 
instruction on x86 and counterparts on other architectures.  Currently 
there is no good portable way of doing this, though I have code floating 
around that I really should package for that purpose specifically.

I'm rather surprised that glibc hasn't been patched to make use of the 
relevant instructions.  RDTSC takes about 22 cycles on a PIII proc, 
possibly less on a P4 (haven't checked in a long time), and the 64-bit 
math necessary is probably not much more lengthy.  Then again 
get_program_time is already performing the equivalent math anyway, a 
conversion would just involve different "constants".

However, I can see that a libc version would be complicated by 
threading, and would require TLS (Thread Local Storage) to work 
properly.  Oh well.

I would assume that by bypassing get_program_time you lose some kind of 
functionality (haven't used simulavr myself yet), but I guess the 
physical simulation time really isn't important, compared to the 
measured *target* cycle times...