Re: [lowrisc-dev] BRAM logic in chip_top.sv

Hi Ahmed, Glad to hear that you find it interesting. I could probably spend the rest of the week talking about FuseSoC (just ask anyone who has been to ORConf :)), but I'll try to answer your questions short and informative. Please let me know where I can fill in details. Regarding modularity, it is supposed to be quite easy to add new tool backends and providers (methods for getting cores from remote sources). I'm currently working on adding support for a new core description format (a side effect of that is that it will be easier to plug in other core description formats as well) and generators, which is a facility to run external preprocessing functions, such as Chisel/Migen/MyHDL/IP-XACT->verilog generation or similar. One of the main goals of FuseSoC is battling the bad practices of dependency management which are prevelent among RTL designers. The most common ways are either to just dump code together will all dependencies in a big repo, or use submodules, but those are both quite clunky mechanisms. Especially when you're starting to have many cores that depend on some common functionality. FuseSoC resolves dependencies just as your normal software package manager would do, with version ranges (e.g. at least verison 2.5, exactly version 4.1 or anything but version 2.4) For information, I packaged version 1 of the complete Pulpino ecosystem already almost three years ago, and I have version 2.1 mostly packaged last year, but never found time to clean up and upload. The ambition in the LowRISC context is of course to package all of LowRISC to be used with FuseSoC and thereby reusing the packaging work already done on Pulpino. My hope is that once package management becomes more common in the open source silicon world, people will stop writing so much new code and just reuse existing stuff. Much more to say, but I'll leave it here :) //Olof On Thu, Nov 23, 2017 at 12:22 PM, Ahmed Khalaf <me(a)ahmedkhalaf.com <mailto:me@ahmedkhalaf.com>> wrote: Dear Olof, I checked the FuseSOC intro, it seems really interesting. Especially its extendable and can help building on different tool-chains and FPGA flows. The task of porting a SoC design to a different device is not an easy task, so in what aspects can FuseSOC help? Also, how modular is "modular"? this is in particular is interesting because of the increasing importance of updates and dependency tracking in a growing community. We had an interesting discussion earlier this month that could be relevant to this: https://listmaster.pepperfish.net/pipermail/lowrisc-dev-lists.lowrisc.org... <https://listmaster.pepperfish.net/pipermail/lowrisc-dev-lists.lowrisc.org... Thank you Regards, Ahmed Khalaf On Thu, Nov 23, 2017 at 12:57 PM, Dr Jonathan Kimmitt <jrrk2(a)cam.ac.uk <mailto:jrrk2@cam.ac.uk>> wrote: Dear Olof,   Our simulator of choice is verilator. We only use XSim when VHDL components are instantiated (such as for DDR controller simulation). All our memories take advantage of the Xilinx feature of being preloadable and writable. We would have to change this when we reach ASIC ready stability. Verilator does not support true dual-port RAM easily because of the way it schedules changes. So the situation when ADD_MINION_SD is enabled is not simulatable in Verilator. We will be looking for a different solution in our next release. The purpose in this case is to provide two way communication through dual-port RAM between Rocket and Minion processors. Jonathan Ok, so you are looking at creating a tool-agnostic RAM with initial contents, with byte enable, configurable width and depth which can also be used by vendor tools for post-implementation initialization? The good part is that I spent quite some time doing something very similar a few years ago. The bad part is that I found it was in practice impossible to do this in a tool-agnostic way. Either, the byte enable signals were ignored, or it didn't map efficiently to RAM resources in ISE, Quartus or Vivado. My conclusion was that it is actually better to do this as a tech-agnostic frontend with selectable backends using available FPGA primitives and a fallback to pure HDL for simulation. (In a wider scope this is one situation where my dream of HDL standard libraries would be very beneficial :) http://olofkindgren.blogspot.com/2017/01/the-dream-of-hdl-standard-librar... <http://olofkindgren.blogspot.com/2017/01/the-dream-of-hdl-standard-librar...>) Right now I also see that there are explicit instantiations of Xilinx primitives when ADD_MINION_SD is defined which means that it's not really tech-agnostic anyway. I would like to rewrite this part as a stand-alone component instead. Can't promise to find the time, but if I do, could you tell me a bit more about the details of this implementation. I sense that there is some extra trickery going on here that I haven't fully grasped yet. Are you trying to append two memories to a larger one when ADD_MINION_SD is defined? Do you need ISim support (the simulator in ISE) or is it really XSim (the simulator in Vviado) support you refer to with the comments? Do you want it as a RAM or would a ROM be good enough? //Olof