colwell@uunet.UUCP (Robert Colwell) (03/29/88)
We built in to the TRACE VLIW a facility that we call the PCQ, short for Program Counter Queue. This set of about 20 MSI chips and RAMs can collect 2K PC values. The user of this facility can control the start and stop criteria, such as starting collection on a given PC value and waiting N clocks afterwards before shutting down the PCQ. Other scanloop tools then dump the contents for analysis. We also provided this hardware with the ability to trap the CPU when half full. The trap handler then knows to dump the PCQ before allowing that user process to continue -- this mode is very useful for program tracing, instruction cache modelling and experimentation, and linker tweaking. There's lots more to it, but perhaps you get the idea. I am writing a paper describing this facility, but I'm having some trouble placing it in its proper context. In other words, what similar facilities have other manufacturers provided (and reported on)? I've heard, for instance, that the VAXes have a bus monitor built into the SBI such that the last N transfers are available for diagnosis. But I've not seen this reported in print. Cargill and Locanthi's ASPLOS-II paper is in the same spirit, but what we've provided is so far beyond what they're suggesting it's almost funny. Does anyone have references that would help? Thanks a lot. Bob Colwell mfci!colwell@uunet.uucp Multiflow Computer 175 N. Main St. Branford, CT 06405 203-488-6090