Merge pull request #181 from pipsoft/master
Improving Documentation on Using BSCANE2 with Murax and OpenOCD
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Dolu1990
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# Implementing VexRiscv Based Murax SoC on Arty A7 Artix-7 PCB from Digilent and Enabling JTAG Connection through Xilinx’s BSCANE2 Debug IP
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**By**<br>
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**Pradeep Krishnamurthy – Student Research Assistant, OFFIS e.V.**<br>
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**Frank Poppen – Senior Research Engineer, OFFIS e.V.**<br>
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**www.offis.de**
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Acknowledgement
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This work was supported in part by the German Federal Ministry of Education and Research (BMBF) within the project
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SATiSFy under contract no. 16KIS0821K, and within the project Scale4Edge under contract no. 16ME0127.
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## 1. Introduction
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Up-to-date FPGA evaluation boards, like the Digilent Arty A7 mounting a Xilinx Artix-7 FPGA, come with an integrated
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FTDI chip which makes programming and debugging quite easy. In our work, we synthesized the VexRiscv based Murax
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processor to an Artix-7 FPGA and at first lead out the JTAG relevant signals of the Riscv core to the board’s Pmod
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Header to connect to a dedicated Olimex JTAG Adapter through a second USB cable. As it turns out, this extra effort
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on hardware can be minimized by use of some Xilinx Debug IP named BSCANE2. Collecting the required information on how
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to do this was tedious. So we came to the decision to document our path to success with this short report. We expect
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that the reader is familiar with the README.md to be found at https://github.com/SpinalHDL/VexRiscv and that the
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reader is capable of generating the Murax SoC as it is described there.
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## 2. SpinalHDL - Generation of Murax SoC with BSCANE2
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The BSCANE2 allows access between the internal FPGA logic and the JTAG Boundary Scan logic controller. This allows
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for communication between the internally running design and the dedicated JTAG pins of the FPGA.
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### Steps to enable Bscane2
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After cloning all files from https://github.com/SpinalHDL/VexRiscv, go to the path: `src/main/scala/vexriscv/demo`
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and find the `Murax.scala` file.
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* Comment out the following lines to remove the toplevel jtag I/O pins in `Murax.scala`. Be aware that line numbers
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as given could move with future changes to the file:
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```
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[164] val jtag = slave(Jtag())
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…
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[392] val jtagClkBuffer = SB_GB()
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[393] jtagClkBuffer.USER_SIGNAL_TO_GLOBAL_BUFFER <> io.jtag_tck
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[394] jtagClkBuffer.GLOBAL_BUFFER_OUTPUT <> murax.io.jtag.tck
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…
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[398] murax.io.jtag.tdi <> io.jtag_tdi
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[399] murax.io.jtag.tdo <> io.jtag_tdo
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[400] murax.io.jtag.tms <> io.jtag_tms
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```
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* In the `Murax.scala` file, delete the line:
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```
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[253] io.jtag <> plugin.io.bus.fromJtag()
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```
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* And add the lines:
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```
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[254] val jtagCtrl = JtagTapInstructionCtrl()
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[255] val tap = jtagCtrl.fromXilinxBscane2(userId = 2)
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[256] jtagCtrl <> plugin.io.bus.fromJtagInstructionCtrl(ClockDomain(tap.TCK))
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```
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Changing the above lines, removes the Murax SoC’s JTAG ports as pins of the FPGA and inserts the BSCANE2 Xilinx
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Debug IP to which the JTAG signals are now connected.
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* Add the following import statement at the beginning of `Murax.scala`:
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```
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import spinal.lib.com.jtag.JtagTapInstructionCtrl
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```
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With these changes in place, you generate the SoC with a demo program already in ram by use of:
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```
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sbt "runMain vexriscv.demo.MuraxWithRamInit"
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```
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A Verilog file is generated with the name `Murax.v` next to four `.bin` files inside the `VexRiscv` folder. These
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files are the input to the Xilinx FPGA synthesis. Inside the `Murax.v` file, we can see that the BSCANE2 ports are
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instantiated, confirming that the BSCANE2 has successfully been instantiated within the Murax SoC as a debug brige
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to JTAG.
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## 3. Xilinx Vivado - Programming Arty A7 FPGA
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There are many applications to program a FPGA. In our work we referred to the freely available Xilinx Vivado 2020
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application to synthesize and program the FPGA. Vivado is readily available at Xilinx website and free of cost to
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download. This document assumes that the reader is able to setup and execute FPGA synthesis projects. The
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following is not a step by step tutorial, but gives general guiding information.
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### Programming the FPGA
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* Create a new project and choose the board. In our case it is the Arty A7-35 (`xc7a35ticsg324-1L`).
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* Copy the mentioned files (.v and .bin) of the previous section from the Vexriscv folder into the Vivado project
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in e.g. the path: `project_name.srcs\sources_1\imports\Downloads`
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* Create a toplevel file by instantiating Murax I/O ports in it to blink the LED’s on the Digilent board. (Note: The program to blink the LED’s is already present in the four `.bin` files with the `Murax.v` file). The toplevel file and constraint `arty_a7.xdc` file, if required, can be found and reused from the path: `VexRiscv/scripts/Murax/arty_a7`, but you need to make sure that all the JTAG ports of Murax are commented or deleted in the toplevel file. Remember: we removed them in Section 2 and connected them internally to the BSCANE2 debug bridge.
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* Be aware that line numbers as given could move with future changes to the file. The lines to remove from toplevel file are:
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```
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[43] reg tesic_tck,tesic_tms,tesic_tdi;
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[44] wire tesic_tdo;
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[45] reg soc_tck,soc_tms,soc_tdi;
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[46] wire soc_tdo;
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[47]
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[48] always @(*) begin
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[49] {soc_tck, soc_tms, soc_tdi } = {tck,tms,tdi};
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[50] tdo = soc_tdo;
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[51] end
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…
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[56] .io_jtag_tck(soc_tck),
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[57] .io_jtag_tdi(soc_tdi),
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[58] .io_jtag_tdo(soc_tdo),
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[59] .io_jtag_tms(soc_tms),
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```
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* Also remove any JTAG port to pin assignments from any constraint file.
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* Next, click Generate Bitstream and program the FPGA with the bit file. You can see the LED’s blink and Murax SoC has been programmed into the FPGA.
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### 4. Debugging - Using OpenOCD and GDB
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* Clone and setup openocd with the steps as provided by https://github.com/SpinalHDL/openocd_riscv
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* You basically have to provide two files for OpenOCD to connect successfully through the FPGA into the Murax SoC inside it:
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1. `usb_connect.cfg` (interface configuration)
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2. `soc_init.cfg` (take over the control of the CPU)
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* `usb_connect.cfg`
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You can take it from ... https://github.com/SpinalHDL/SaxonSoc/blob/dev-0.3/bsp/digilent/ArtyA7SmpLinux/openocd/usb_connect.cfg ... without modifications as we would say. Be aware that it includes the two files `xilinx-xc7.cfg` and `jtagspi.cfg` which are part of the OpenOCD project ... https://github.com/riscv/riscv-openocd/tree/riscv/tcl/cpld , but make sure to check the path for the files. If required, adapt the find and path for the lines:
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```
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[29] source [find cpld/xilinx-xc7.cfg]
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[30] source [find cpld/jtagspi.cfg]
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```
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* `soc_init.cfg`
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https://github.com/SpinalHDL/SaxonSoc/blob/dev-0.3/bsp/digilent/ArtyA7SmpLinux/openocd/soc_init.cfg
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You can take it but you need to: `set cpu_count to 1` and remove lines 22 to 35 as shown in the result below:
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```
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set cpu_count 1
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for {set i 0} {$i < $cpu_count} {incr i} {
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target create saxon.cpu$i vexriscv -endian little -chain-position $TAP_NAME -coreid $i -dbgbase [expr $i*0x1000+0x10B80000]
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vexriscv readWaitCycles 40
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vexriscv cpuConfigFile $CPU0_YAML
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if {$SPINAL_SIM != "yes"} {
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vexriscv jtagMapping 3 3 0 1 2 2
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}
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}
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for {set i 0} {$i < $cpu_count} {incr i} {
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targets saxon.cpu$i
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poll_period 50
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init
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soft_reset_halt
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}
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puts " done"
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```
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* Run openocd:
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```
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openocd -c "set CPU0_YAML ../VexRiscv/cpu0.yaml" \
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-f tcl/interface/usb_connect.cfg \
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-f tcl/interface/soc_init.cfg
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```
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On success you should be able to see something like
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```
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Open On-Chip Debugger 0.10.0+dev-01231-gf8c1c8ad-dirty (2021-05-03-10:57)
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Licensed under GNU GPL v2
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For bug reports, read
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http://openocd.org/doc/doxygen/bugs.html
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../../cpu0.yaml
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Info : auto-selecting first available session transport "jtag". To override use 'transport select <transport>'.
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xc7.tap
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Info : set servers polling period to 50ms
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Info : clock speed 5000 kHz
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Info : JTAG tap: xc7.tap tap/device found: 0x0362d093 (mfg: 0x049 (Xilinx), part: 0x362d, ver: 0x0)
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Info : starting gdb server for saxon.cpu0 on 3333
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Info : Listening on port 3333 for gdb connections
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requesting target halt and executing a soft reset
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done
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Info : Listening on port 6666 for tcl connections
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Info : Listening on port 4444 for telnet connections
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```
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* Information on setting up a riscv compiler and debugger toolchain are to be found at:
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https://github.com/riscv/riscv-gnu-toolchain
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* With openocd running you can now connect a debugger to `port 3333`.
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* A demonstration software to compile and debug with the Murax SoC can be found at https://github.com/SpinalHDL/VexRiscvSocSoftware in the path `VexRiscvSocSoftware/projects/murax/demo`. With a `make` you create the `.elf` in the `build` directory from which you then give the command:
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```
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riscv64-unknown-elf-gdb demo.elf
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```
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* The riscv debugger is started with the `demo.elf` program and is ready to be connected to the CPU. Do so by issuing the following command in its window:
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* `target remote localhost:3333` This command will connect the GDB server to OpenOCD
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* `load` This command will load the program into the FPGA. Whenever you decide to make changes to the demo software and recompiled it, you need to upload the resulting new executable to the CPU in this way.
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* `monitor reset halt` This command resets the Murax CPU and halts it to receive further commands.
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* `continue` From here on you should be able to execute a regular debug session with your VexRiscv based Murax SoC on the FPGA.
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@ -1,138 +0,0 @@
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1. INTRODUCTION
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In recent times, modern FPGA’s come with an integrated FTDI chip which makes debugging easy with only a USB cable, thereby reducing an unnecessary extra hardware (JTAG Adapter).
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In this document, I am going to guide you through the steps in an experiment which I conducted along with my supervisor to debug an SoC named MURAX without using an external JTAG adapter on ARTY A7 FPGA.
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2. Generation of Bscane2 within Murax SoC in Linux
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The BSCANE2 allows access between the internal FPGA logic and the JTAG Boundary Scan logic controller. This allows for communication between the internal running design and the dedicated JTAG pins of the FPGA.
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Steps to create Bscane2
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• After cloning all the files from https://github.com/SpinalHDL/VexRiscv, go to this path : src/main/scala/vexriscv/demo and find the Murax.scala file.
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• Comment out the following lines to remove the toplevel jtag I/O pins in Murax.scala
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val jtag = slave(Jtag())
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val jtagClkBuffer = SB_GB()
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jtagClkBuffer.USER_SIGNAL_TO_GLOBAL_BUFFER <> io.jtag_tck
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jtagClkBuffer.GLOBAL_BUFFER_OUTPUT <> murax.io.jtag.tck
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murax.io.jtag.tdi <> io.jtag_tdi
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murax.io.jtag.tdo <> io.jtag_tdo
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murax.io.jtag.tms <> io.jtag_tms
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• In the Murax.scala file, delete the below line:
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io.jtag <> plugin.io.bus.fromJtag()
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And add the following lines :
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val jtagCtrl = JtagTapInstructionCtrl()
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val tap = jtagCtrl.fromXilinxBscane2(userId = 2)
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jtagCtrl <> plugin.io.bus.fromJtagInstructionCtrl(ClockDomain(tap.TCK))
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By deleting the line (io.jtag <> plugin.io.bus.fromJtag() ) and adding the above lines, the Murax SoC’s Jtag ports are removed and a Bscane2 bridge will be created inside the Murax SoC itself, thereby avoiding to add the Bscane2 IP while programming the FPGA.
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• Add the following import statement at the beginning in Murax.scala :
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import spinal.lib.com.jtag.JtagTapInstructionCtrl
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• Then to generate the SoC with a demo program already in ram, run:
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sbt "runMain vexriscv.demo.MuraxWithRamInit"
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• A verilog file will be generated with the name Murax.v and four .bin files will be generated inside VexRiscv folder which can be used to program the FPGA. Inside the Murax.v file, we can see that the Bscane2 ports will be instantiated, confirming that the Bscane2 has been created within the Murax SoC to debug it.
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3. Programming Arty A7 FPGA
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There are many applications to program a FPGA. I am using Xilinx Vivado 2020 Application to program the FPGA, which is an open source application and is readily available in Xilinx website and free of cost to download.
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Steps involved to program the FPGA
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• Create a new project and choose the board which are using and choose the constraint file.
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• As, I mentioned in the previous section a verilog file and four .bin files will be generated in the Vexriscv folder. Copy these files and paste them inside your vivado project in this path : project_name.srcs\sources_1\imports\Downloads
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• Create a toplevel file by instantiating Murax I/O ports in it to blink the LED’s on the FPGA. (Note : The program to blink the LED’s is already present in Murax.v file). The toplevel file and constraint file, if required can be found in this path :VexRiscv/scripts/Murax/arty_a7 , but make sure all the jtag ports of Murax are commented or deleted in the toplevel file.
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• The lines to remove from toplevel file are :
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reg tesic_tck,tesic_tms,tesic_tdi;
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wire tesic_tdo;
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reg soc_tck,soc_tms,soc_tdi;
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wire soc_tdo;
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always @(*) begin
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{soc_tck, soc_tms, soc_tdi } = {tck,tms,tdi};
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tdo = soc_tdo;
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end
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.io_jtag_tck(soc_tck),
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.io_jtag_tdi(soc_tdi),
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.io_jtag_tdo(soc_tdo),
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.io_jtag_tms(soc_tms),
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• Next, click Generate Bitstream and program the FPGA with the bit file. You can see the LED’s blink and Murax SoC has been programmed into the FPGA.
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4. Debugging via OpenOCD GDB in Linux
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• In a new terminal in Linux, after cloning and setting up openocd with the steps provided in this link : https://github.com/SpinalHDL/openocd_riscv , run the below command to establish a openocd connection with JTAG of FPGA.
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• You basically have to provide 2 files.
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usb_connect.cfg => interface configuration
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soc_init.cfg => take over the control of the CPU
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• For usb_connect.cfg
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you can take it from https://github.com/SpinalHDL/SaxonSoc/blob/dev-0.3/bsp/digilent/ArtyA7SmpLinux/openocd/usb_connect.cfg (without modifications I would say, but make sure to check the entire path in your system for the files
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xilinx-xc7.cfg and jtagspi.cfg) and write it as below, remove the word “find” and the square brackets.
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source ../openocd_riscv/tcl/cpld/xilinx-xc7.cfg
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source .. /openocd_riscv/tcl/cpld/jtagspi.cfg
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• For soc_init.cfg
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https://github.com/SpinalHDL/SaxonSoc/blob/dev-0.3/bsp/digilent/ArtyA7SmpLinux/openocd/soc_init.cfg
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You can take it but you need to : set cpu_count to 1 and remove Line 22 to 35 as shown below :
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set cpu_count 1
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for {set i 0} {$i < $cpu_count} {incr i} {
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target create saxon.cpu$i vexriscv -endian little -chain-position $TAP_NAME -coreid $i -dbgbase [expr $i*0x1000+0x10B80000]
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vexriscv readWaitCycles 40
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vexriscv cpuConfigFile $CPU0_YAML
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if {$SPINAL_SIM != "yes"} {
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vexriscv jtagMapping 3 3 0 1 2 2
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}
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}
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for {set i 0} {$i < $cpu_count} {incr i} {
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targets saxon.cpu$i
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poll_period 50
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init
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soft_reset_halt
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}
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puts done
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• To run openocd :
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Use the below command :
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src/openocd -c "set CPU0_YAML ../VexRiscv/cpu0.yaml" -f tcl/interface/usb_connect.cfg -f tcl/interface/soc_init.cfg
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• Prequisites to have before executing the next steps can be found here :
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https://github.com/riscv/riscv-gnu-toolchain
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• Then, after openocd is running, in new terminal, follow the below commands in VexriscvSocSoftware folder ( https://github.com/SpinalHDL/VexRiscvSocSoftware ).
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• Go to the path VexRiscvSocSoftware/projects/murax/demo/build and then give the below commands :
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riscv64-unknown-elf-gdb demo.elf
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- This command will initiate the already written demo program to blink the LED’s on the FPGA.
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target remote localhost:3333
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- This command will connect the GDB server
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load
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- This command will load the program into the FPGA
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monitor reset halt
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- This command will halt the blinking of LED’s
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continue
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- This command will continue the blinking of LED’s from the point it stopped.
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By,
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Pradeep Krishnamurthy - Research Assistant, Offis e.V
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Frank Poppen - Senior Research Engineer, Offis e.V
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@ -1,3 +1,9 @@
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if [info exists env(SPINAL_SIM)] {
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set SPINAL_SIM $::env(SPINAL_SIM)
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} else {
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set SPINAL_SIM no
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}
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set cpu_count 1
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@ -1,4 +1,4 @@
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interface ftdi
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adapter driver ftdi
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ftdi_device_desc "Digilent USB Device"
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ftdi_vid_pid 0x0403 0x6010
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ftdi_channel 0
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@ -6,7 +6,7 @@ ftdi_layout_init 0x00e8 0x60eb
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ftdi_tdo_sample_edge falling
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reset_config none
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adapter_khz 5000
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adapter speed 5000
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source [find cpld/xilinx-xc7.cfg]
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source [find cpld/jtagspi.cfg]
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