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When it comes time to send a packet with the i8254xGBe model hooked up to EtherTap and while running in KVM mode, the packet will first go to the EtherTap over the network style port between them. EtherTap, because it's not actually a model of anything in the simulation, will immediately pass the packet off to the real network and report that the transmission was successful to the i8254xGBe. The i8254xGBe will notice that it still has stuff it can send (the KVM mode CPU has no trouble keeping it full) and will, without returning and collapsing the stack, immediately call back into EtherTap with the next packet. This loop repeats, continually deepening the stack, until gem5 crashes with a segfault. To break this loop, a few small changes have been made. First, txFifoTick has been repurposed slightly so that it continuously keeps track of whether there's still work to do to flush out the fifo during the current tick. The code in txWire has been adjusted slightly so that it clears that variable at the start (also removing some redundancy), so that other code can set it again if more work needs to be done. Specifically, the ethTxDone function will set that flag. If there's more work to be done flushing the Fifo while in tick(), it will loop until txFifoTick stays cleared, meaning either the Fifo is empty, or the object on the other end hasn't said it's done yet. Finally, a new bool member called inTick has been added which keeps track of whether the tick() function is still active somewhere in the callstack. If it is, then the tick event shouldn't be rescheduled in ethTxDone, since tick will take care of that before it returns. It won't check to see if it needs to, and so without this check there's a panic from scheduling the same event twice. It's not completely clear that the Fifo should send packets over and over as fast as the other side accepts them within the same tick, although it's not clear that it shouldn't either. If not, then probably all that would need to change would be to remove the "while" loop so that the tick event would be rescheduled, and the Fifo would be further emptied the next time around. Change-Id: I653379b43389d0539ecfadb3fc6c40e38a8864c2 Reviewed-on: https://gem5-review.googlesource.com/3642 Reviewed-by: Andreas Hansson <andreas.hansson@arm.com> Maintainer: Gabe Black <gabeblack@google.com>
This is the gem5 simulator. The main website can be found at http://www.gem5.org A good starting point is http://www.gem5.org/Introduction, and for more information about building the simulator and getting started please see http://www.gem5.org/Documentation and http://www.gem5.org/Tutorials. To build gem5, you will need the following software: g++ or clang, Python (gem5 links in the Python interpreter), SCons, SWIG, zlib, m4, and lastly protobuf if you want trace capture and playback support. Please see http://www.gem5.org/Dependencies for more details concerning the minimum versions of the aforementioned tools. Once you have all dependencies resolved, type 'scons build/<ARCH>/gem5.opt' where ARCH is one of ALPHA, ARM, NULL, MIPS, POWER, SPARC, or X86. This will build an optimized version of the gem5 binary (gem5.opt) for the the specified architecture. See http://www.gem5.org/Build_System for more details and options. With the simulator built, have a look at http://www.gem5.org/Running_gem5 for more information on how to use gem5. The basic source release includes these subdirectories: - configs: example simulation configuration scripts - ext: less-common external packages needed to build gem5 - src: source code of the gem5 simulator - system: source for some optional system software for simulated systems - tests: regression tests - util: useful utility programs and files To run full-system simulations, you will need compiled system firmware (console and PALcode for Alpha), kernel binaries and one or more disk images. Please see the gem5 download page for these items at http://www.gem5.org/Download If you have questions, please send mail to gem5-users@gem5.org Enjoy using gem5 and please share your modifications and extensions.