[Gems-users] conflicting interrupts in simulated system when running GEMS/simics

[Philip Garcia <pcgarcia@xxxxxxxx>]

Hello,
I am experiencing an interesting problem, and was wondering if anyone  
else has experienced similar problems.   If I'm running simulations in  
GEMS 2.1/simics 3.0.31 using a bagle (ultrasparc linux) target.  The  
issue I've noted is a very rare occurrence, but appears to happen if a  
timer interrupt occurs at the same time another system interrupt  
occurs.  In general, the only external interrupt I see is the UART  
interrupt, which is triggered when applications write to the simics  
console.  Under the proper circumstances I've noticed that the UART  
interrupt will basically lock up (freezing the firehose controller  
that issues interrupts), and halts outputting to the console.  The  
application that initiated the UART write will lock up as well, as it  
is unable to finish outputting to the console.  In my system, I rely  
on other interrupts on the firehose controller issuing interrupts,  
which cease to work, causing all simulated processors to eventually  
lock up.  I have prevented this bug from occurring by not issuing my  
interrupts at the same time as timer interrupts and vice versa.   
However, I have no control over the UART interrupts and thus can't  
prevent them from occurring at the same time.  This actual bug occurs  
very rarely in my application (Xvid encoding that only outputs at the  
end of each frame), but it is still noticeable (I experienced it once  
in ~100Billion cycles of simulating a 4 processor system - different  
simulations from the same checkpoint...).
Has anyone else experienced similar behavior when outputting to the  
simulated console when running GEMS?   I know I could "solve" this  
problem by redirecting stdout to /dev/null, but it doesn't seem like  
the ideal solution.  I'm just curious to see if anyone has seen any  
similar (or unexplained) bugs when running their simulations.  The  
best way to notice this has happened is by examining the console  
output from simics, and seeing that the output is obviously truncated  
in unexpected ways (in my case Xvid wrote half the frame information  
to the console and hung up, and this occurred a few hundred million  
cycles before I finished running the simulation).  I will likely cross  
post this over on the simics forum to see if anyone there can help as  
well, but I'd really like to get to the root of what is going on here.
Phil