Rocket Chip on Zynq FPGAs
Warning: This repository is deprecated and does not track Rocket Chip master.
Freedom platform. Those looking for an FPGA-accelerated simulation environment (for obtaining cycle-accurate performance measurements) should use FireSim. Both of these tools regularly update their version of Rocket Chip.Those looking for an FPGA prototype of Rocket Chip should checkout SiFive’s
This repository contains the files needed to run the RISC-V rocket chip on various Zynq FPGA boards (Zybo, Zedboard, ZC706) with Vivado 2016.2. Efforts have been made to not only automate the process of generating files for these boards, but to also reduce duplication as well as the size of this repo. Prebuilt images are available in git submodules, and they are only shallowly cloned if requested.
How to use this README
This README contains 3 major sets of instructions:
Quick Instructions: This is the simplest way to get started - you'll download the relevant prebuilt images for your board and learn how to run binaries on the RISC-V Rocket Core. These instructions require only that you have a compatible board - neither Vivado nor the RISC-V Toolchain are necessary.
Pushing Your Rocket Modifications to the FPGA: These instructions walk through what we believe is the common case - a user wanting to utilize a custom-generated Rocket Core.
Building Everything from Scratch: Here, we discuss how to build the full stack from scratch. It is unlikely that you'll need to use these instructions, unless you are intending to make changes to the configuration of the Zynq ARM Core or
Finally, the bottom of the README contains a set of Appendices, which document some common operations that we believe are useful or provides more depth on commands described elsewhere in the documentation.
Note: If you are seeking to test your own modifications to rocket chip (RC) using this repository, it must be derived from RC commit fb476d1 or later, as this project expects both a debug module to be present, and links directly against RC to build a top-level project directly in chisel. Otherwise, you should use an older version of this repository bf6d00c2 or earlier, which has support for HTIF-based rocket chip instances.
- Overview of System Stack
- 1 - Quick Instructions
- 2 - Pushing Your Rocket Modifications to the FPGA
- 3 - Building Everything from Scratch
Our system will allow you to run a RISC-V binary on a rocket core instantiated on a supported Zynq FPGA. This section will outline the stack of all of the parts involved and by proxy, outline the rest of the documentation. Going top-down from the RISC-V binary to the development system:
RISC-V Kernel (proxy kernel or RISC-V Linux) runs on top of the rocket chip. The proxy kernel is extremely lightweight and designed to be used with a single binary linked against Newlib while RISC-V Linux is appropriate for everything else.
Rocket Chip (rocket core with L1 instruction and data caches) is instantiated on the FPGA. Many of its structures will typically map to various hard blocks including BRAMs and DSP slices. It communicates to the host ARM core on the Zynq via AXI.
Front-end Server (riscv-fesvr) runs on the host ARM core and provides an interface to the rocket chip running on the FPGA (connected via AXI).
Zynq ARM Core (actually dual Cortex A9) runs Linux and simplifies interfacing with the FPGA.
FPGA Board (Zybo, Zedboard, or ZC706) contains the Zynq FPGA and several I/O devices. At power on, the contents of the SD card are used to configure the FPGA and boot Linux on the ARM core.
External Communication (TTY over serial on USB or telnet/ssh over ethernet) allows the development system to communicate with the FPGA board.
Development System (PC with SD card reader) generates the images to configure the FPGA.
Using prebuilt images, run hello world and/or linux on rocket
First, enter into the directory for your board (current options are
zc706). From there, run the following to download all of the necessary images:
$ make fetch-images
Next, insert the SD card on the development system and copy over the images:
$ make load-sd SD=path_to_mounted_sdcard
Finally, eject the SD card, insert it into the board, set the board's boot jumper to "SD", and power the board on. Connect to the board with an ethernet cable (password is root) and run hello world:
$ ssh firstname.lastname@example.org root@zynq:~# ./fesvr-zynq pk hello hello!
Awesome! You can now run RISC-V binaries on Rocket. If you'd like to boot linux on the Rocket core, see Booting Up and Interacting with the RISC-V Rocket Core.
Requires: Vivado 2016.2 and its settings64.sh and a JVM that can run Scala
After you clone the repository for the first time, you must initialize the submodules rocket-chip and testchipip, as well as the first-level submodules of rocket-chip itself.
$ make init-submodules
If you have your own working rocket-chip directory that you would like to use, override the
ROCKET_DIR make variable set in common/Makefrag.
The verilog for the rocket chip is generated by Chisel and thus is not intended to be edited by humans. This project instantiates rocket chip as module larger top level chisel project, that includes an adapter to interface the ARM core with rocket chip's debug module.
The configuration used to generate the rocket chip comes from the
CONFIG environment variables. If
CONFIG isn't set by the environment, it is taken from the
Makefile for the current board. For this example, we use the Zybo which has a default configuration of
Enter into the directory for your board (current options are
zc706). After making changes within
common/src/main/scala, you can run the rocket chip generator and copy the newly generated verilog back into the board's src/verilog directory with:
$ make rocket
You can also explicitly set the
CONFIG variable from the command-line (can do this for any command):
$ make rocket CONFIG=MyFPGAConfig
By default this will look up a configuration specified in the rocket chip library. You may define a custom one without recompiling rocketchip, by defining in the zynq chisel sources at
common/src/main/scala, and instead calling:
$ make rocket CONFIG_PROJECT=zynq CONFIG=MyCustomZynqConfig
The generator will instead look for the configuration definition in the local project instead of the rocket chip library.
To generate a Vivado project specific to the board and the configuration (one project per configuration):
$ make project
This step only needs to be done once per configuration.
Once you have changed the design, you will need to generate a new bitstream and that will need to be packaged in
boot.bin also contains the binaries needed for startup (
u-boot.elf) but these can be reused. From within the board's directory (zybo in this example), to repack
$ make fpga-images-zybo/boot.bin
If you have modified the verilog for your project but not generated a new bitstream,
make should generate a new bitstream automatically. To use the new
boot.bin, copy it to the SD card, insert the SD card into the board, and power on the board.
This section describes how to build the entire project from scratch. Most likely, you will not need to perform all of these steps, however we keep them here for reference. Various other sections of this README may selectively refer to these sections. This section assumes that you've just pulled this repository and have sourced the settings file for Vivado 2016.2.
For ease of exposition, we will be describing all of the commands assuming that we are working with the
zybo and its default configuration
ZynqSmallConfig. Replacing references to the
zc706 will allow you to use these instructions for those boards.
From here on,
$REPO will refer to the location of the
First, we need to generate a Vivado project from the source files that are present in a particular board's directory.
$ cd $REPO/zybo $ make project
Next, let's open up the project in the Vivado GUI:
$ make vivado # OR $ cd zybo_rocketchip_ZynqSmallConfig $ vivado zybo_rocketchip_ZynqSmallConfig.xpr
If you wish to make any modifications to the project, you may now do so. Once you've finished, let's move on:
Inside Vivado, select Open Block Design followed by system.bd in the dropdown. This will open a block diagram for the Zynq PS Configuration and is necessary for correct FSBL generation.
Next, select Generate Bitstream. Vivado will now step through the usual Synthesis/Implementation steps. Upon completion, if you're interested in only the bitstream, you can stop here; the file you want is in:
Otherwise, let's continue on to select Open Implemented Design. This is again necessary to properly export the description of our Hardware for the Xilinx SDK to use.
At this point, select File -> Export -> Export Hardware. This will create the following directory:
This directory contains a variety of files that provide information about the hardware to the SDK. Let's continue on to building the FSBL.
This step assumes that you have just generated the bitstream. Inside the Vivado GUI, select "Launch SDK". This will open up the Xilinx SDK preconfigured with the description of our hardware. In order to generate the FSBL, do the following:
Select File -> New -> Application Project
In the new window, type "FSBL" as the Project name, and ensure that the rest of the properties are correctly set (disregarding the greyed out Location field):
Select Next, at which point you should be given a set of options. Select Zynq FSBL and Finish.
The SDK will proceed to automatically compile the FSBL. You can see the progress in the Console.
Once the build is finished, we need to build u-boot before returning to the SDK in order to create our BOOT.bin.
Returning to the command line, do the following from the directory corresponding to your board:
$ make arm-uboot
This target performs a variety of commands. It will first pull the u-boot source from the Xilinx repositories (see the submodule in
$REPO/common/u-boot-xlnx), patch it with the necessary files found in
$REPO/zybo/soft_config/, compile u-boot, and place the resulting u-boot.elf file in
At this point, we have built up all of the necessary components to create our
boot.bin file. Returning to the Xilinx SDK, select Xilinx Tools -> Create Zynq Boot Image.
First, you should fill in the Output BIF file path with
$REPO/zybo/deliver_output. If this directory has not already been created, you may go ahead and create it (this is where we will place all of the items that we will ultimately transfer to the SD card). See the below for a sample path. Performing this step will also fill in the Output path field, which specifies the location of the
BOOT.bin file that we desire.
Next, we will add the individual files that make up
BOOT.bin. Order is important, so follow these steps exactly:
- Select Add and in the window that opens, click Browse and specify the following location:
Once you have done so select the dropdown next to Partition type and select bootloader. You must perform this step after selecting the path, else the SDK will change it back to datafile, and your
BOOT.bin will not work.
At the conclusion of this step, the Add partition window will look something like:
Click _OK_to return to the previous window.
- Once more, click Add. In the new Add partition window, click Browse and specify the following location:
Ensure that Partition type is set to datafile and click OK.
- Click Add a final time. Click Browse and this time select our compiled
Again, ensure that Partition type is set to datafile and click OK.
- At this point, the window should match the following (click the image to zoom in):
Select Create Image. This will produce a
BOOT.bin file in the
If you make modifications to the project in the future, you can avoid having to perform this step manually and instead may reuse the output.bif file that the SDK generates the first time you use Create Zynq Boot Image. Use the following make target to do so:
$ make deliver_output/boot.bin
As part of our bootstrapping process, we need to boot linux on the ARM core in the Zynq. We can build this copy of linux like so (again assuming that we are in
$ make arm-linux
We additionally need to produce the
devicetree.dtb file that linux will use to setup peripherals of the ARM core. We can produce this like so:
$ make arm-dtb
At this point, the
$REPO/zybo/deliver_output directory contains the following files:
BOOT.bin- (the filename is case insensitive, you may see
boot.bin). This contains the FSBL, the bitstream with Rocket, and u-boot.
uImage- Linux for the ARM PS
devicetree.dtb- Contains information about the ARM core's peripherals for linux.
The only remaining file that we are missing at this point is
uramdisk.image.gz, the root filesystem for linux on the ARM Core. You can obtain it like so (it will be placed in
$ make fetch-ramdisk
Now, take the four files in
deliver_output/, and place them on the root of the SD card that we will insert into the Zybo. The layout of your SD card should match the following:
SD_ROOT/ |-> boot.bin |-> devicetree.dtb |-> uImage |-> uramdisk.image.gz
At this point, you have performed the necessary steps to run binaries on Rocket. See Section 3.8 for how to do so. If you are interested in running riscv-linux on Rocket, continue on to Section 3.7:
There are two options to obtain riscv-linux:
Method 1) Build from Source
To build riscv-linux for Rocket, follow the instructions here. These instructions will show you how to create a linux image that boots from an initramfs. We also now have support for block devices, so you can also boot from an ext2 image created by buildroot. To configure linux to boot from a block device, instead of selecting "Initial RAM filesystem and RAM disk", add the arguments "root=/dev/generic-blkdev rw" to the kernel command line under "Kernel Hacking" -> "Built-in Kernel Command String". To use the block device, you will need to use the ucbbar-all branch of riscv-linux.
Next, you'll need to build an instance of the Berkeley Bootloader(BBL) that contains your linux image as a payload. BBL is provided alongside the proxy kernel at this repository.
Finally, drop your bbl image into SD_ROOT/, which will be mounted as
/mnt/boot/ in the ARM core's filesystem.
Warning: If you are working with the Zybo, you need to make sure you compile with a version of the riscv-gnu-toolchain that targets RV64IMA, as the zybo configuration does not possess an FPU.
Method 2) Use the provided BBL instance
Included in the home directory of the ARM core's ramdisk we've provided an instance of bbl preloaded with a miniminal linux image. All you have to do is follow the instructions in the next section.
First, insert the SD card and follow the instructions in Appendix A to connect to your board. You can login to the board with username root and password root. Once you're at the prompt, you can run a basic hello world program on rocket like so:
root@zynq:~# ./fesvr-zynq pk hello hello!
To boot riscv-linux, run:
root@zynq:~# ./fesvr-zynq bbl vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv vvvvvvvvvvvvvvvvvvvvvvvvvvvv rrrrrrrrrrrrr vvvvvvvvvvvvvvvvvvvvvvvvvv rrrrrrrrrrrrrrrr vvvvvvvvvvvvvvvvvvvvvvvv rrrrrrrrrrrrrrrrrr vvvvvvvvvvvvvvvvvvvvvvvv rrrrrrrrrrrrrrrrrr vvvvvvvvvvvvvvvvvvvvvvvv rrrrrrrrrrrrrrrrrr vvvvvvvvvvvvvvvvvvvvvvvv rrrrrrrrrrrrrrrr vvvvvvvvvvvvvvvvvvvvvv rrrrrrrrrrrrr vvvvvvvvvvvvvvvvvvvvvv rr vvvvvvvvvvvvvvvvvvvvvv rr vvvvvvvvvvvvvvvvvvvvvvvv rr rrrr vvvvvvvvvvvvvvvvvvvvvvvvvv rrrr rrrrrr vvvvvvvvvvvvvvvvvvvvvv rrrrrr rrrrrrrr vvvvvvvvvvvvvvvvvv rrrrrrrr rrrrrrrrrr vvvvvvvvvvvvvv rrrrrrrrrr rrrrrrrrrrrr vvvvvvvvvv rrrrrrrrrrrr rrrrrrrrrrrrrr vvvvvv rrrrrrrrrrrrrr rrrrrrrrrrrrrrrr vv rrrrrrrrrrrrrrrr rrrrrrrrrrrrrrrrrr rrrrrrrrrrrrrrrrrr rrrrrrrrrrrrrrrrrrrr rrrrrrrrrrrrrrrrrrrr rrrrrrrrrrrrrrrrrrrrrr rrrrrrrrrrrrrrrrrrrrrr INSTRUCTION SETS WANT TO BE FREE [ 0.000000] Linux version 4.6.2 <more messages follow>
After linux boots you'll be presented with a busybox prompt from riscv-linux running on rocket!
If you are using a root filesystem on a seperate filesystem image, you can boot linux by running
root@zynq:~# ./fesvr-zynq +blkdev=rootfs.ext2 bbl
On the Zybo and Zedboard a single serial-USB cable is needed but on the ZC706 you will also need a USB type A to type B cable (and possibly some drivers). To connect:
$ screen /dev/tty.usbmodem1411 115200,cs8,-parenb,-cstopb
Note: The numbers following
tty.usbmodem may vary slightly. On the Zybo,
usbserial- and on the ZC706, replace it with
The board has an IP of 192.168.1.5 and can be accessed by username/password of root/root on telnet and ssh. For example:
$ ssh email@example.com
Note: Make sure your development system ethernet interface is configured to be on the 192.168.1.x subnet. The default configuration intends for the board to be directly attached to the development system (single cable). If you want to place the board on a larger network, we recommend changing the root password to something stronger and changing the IP configuration to mesh well with your network.
Copying Files over Ethernet
The easiest way to get a file onto the board is to copy it with scp over ethernet:
$ scp file firstname.lastname@example.org:~/
Note: Linux is running out of a RAMdisk, so to make a file available after a reboot, copy it to the SD card or modify the RAMdisk.
Changing the RAMDisk
Requires: u-boot and sudo
The RAMDisk (
uramdisk.image.gz) that holds Linux for the ARM cores is a gzipped cpio archive with a u-boot header for the board. To open the RAMdisk:
$ make ramdisk-open
When changing or adding files, be sure to keep track of owners, groups, and permissions. When you are done, to package it back up:
$ make ramdisk-close
A useful application of this is to add your SSH public key to
.ssh/authorized_keys so you can have passwordless login to the board.
Note: Since these ramdisk operations use sudo on files, they may not work on a network mounted filesystem. To get around this limitation, it is easiest to just copy it to a local filesystem when modifying the ramdisk.
Requires: Vivado 2016.2 and its settings64.sh sourced
First, enter into the directory for your board (current options are
zc706). To generate a bitstream, you will need a Vivado project. You should only need to generate it once, but the automation this repo provides makes it easy to generate again if you delete the project. To generate a Vivado project from scratch:
$ make project
To generate a bitstream from the command-line:
$ make bitstream
To launch Vivado in GUI mode:
$ make vivado
You can change the clockrate for the rocket chip by changing
RC_CLK_DIVIDE within a board's
src/verilog/clocking.vh. After that change, you will need to generate a new bitstream (and
Note: Although rarely needed, it is possible to change the input clockrate to the FPGA by changing it within the block design,
src/verilog/clocking.vh. This will also require regenerating
FSBL.elf, the bitstream, and of course
The SD card is used by the board to configure the FPGA and boot up the ARM core. All of these files are available within a board's fpga-images submodule, but they can also be built from scratch. Here is a summary of the files and their purposes:
boot.binis generated by the Xilinx SDK and is actually three files. To generate it from scratch, follow the instructions from Section 3 up through Section 3.5 Creating boot.bin. To repack it from existing components, follow Repacking boot.bin.
- Bitstream (
rocketchip_wrapper.bit) configures the FPGA with the rocket chip design. To build it with the GUI, see Section 3.2 Generating a Bitstream and to build it with the command-line, see: Working with Vivado.
- First Stage Bootloader (
FSBL.elf) - This bootloader configures the Zynq processing system based on the block design in the Vivado project. The FSBL will hand-off to
u-bootonce the processing system is setup. We build the FSBL using the Xilinx SDK and hardware information exported from Vivado. (see Section 3.3)
- u-boot (
u-boot.elf) - This bootloader takes configuration information and prepares the ARM processing system for booting linux. Once configuration is complete,
u-bootwill hand-off execution to the ARM linux kernel. We build
u-bootdirectly from the Xilinx u-boot repository, with some configuration modifications to support Rocket. (see Section 3.4)
- Bitstream (
- ARM Linux (
uImage) - This is a copy of linux designed to run on the ARM processing system. From within this linux environment, we will be able to run tools (like
fesvr-zedboard) to interact with the RISC-V Rocket Core. We build directly from the Xilinx linux repository, with a custom device tree file to support Rocket. (see Section 3.6)
- ARM RAMDisk (
uramdisk.image.gz) - The RAMDisk is mounted by ARM Linux and contains the root filesystem. For obtaining it, see Section 3.6, and for modifying it, see Appendix B.
devicetree.dtb- Contains information about the ARM core's peripherals for Linux. (See Section 3.6)
The riscv-fesvr repo provides against which the zynq-fesvr is linked. Additionally,
common/csrc includes source for main, and a simple driver, which hands off debug module requests and reponses between the ARM core and rocket chip. Before building, make sure the 2016.2 version of settings64.sh is sourced. To build the riscv-fesvr binary for Linux ARM target (to run on Zynq board), type:
$ make fesvr-zynq
and make sure you have the Xilinx SDK in your PATH, and the riscv-tools/riscv-fesvr submodule initialized in your rocket chip directory. When installing fesvr-zynq, don't forget to copy the library as well (
/usr/local/lib on the board).
The Zybo build was last tested with this version of the toolchain.
Because the Zybo board uses
ZynqSmallConfig, riscv-tools must be recompiled to omit floating point instructions. Add the
--with-arch=RV64IMA tag to the line in
build.sh that builds riscv-gnu-toolchain. It should read as follows:
build_project riscv-gnu-toolchain --prefix=$RISCV --with-arch=RV64IMA
./build.sh as normal.
When testing on spike, run spike with the
If pk does not work, make sure it is being built using this version of the toolchain, since it is specifically generated to not have floating point instructions. Also make sure any binaries you want to run on the Zybo are compiled using this toolchain.
In addition to those that contributed to rocket chip, this repository is based on internal repositories contributed by:
- Rimas Avizienis
- Jonathan Bachrach
- David Biancolin
- Scott Beamer
- Sagar Karandikar
- Deborah Soung
- Andrew Waterman