OVERVIEW
This tutorial shows how to use Xilinx FPGA (Nexys3 board). In this example, we will run a soft core called PicoBlaze on Nexys3 and then light 8 LEDs. Code for this part is here
REQUIREMENTS
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Nexys3 | FPGA Board with Xilinx Spartan-6 FPGA |
ISE | IDE tool used to develop FPGA applications |
Adept | Tool to download bit file into FPGA |
Verilog| HDL to develop FPGA application |
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STEP 1: Download PicoBlaze Source Code
Go to the PicoBlaze Page to download the KCPSM6 ... zip file.
NOTE: There are several helpful materials in the source code file. For example, KCPSM6_User_Guide includes general design flow with PicoBlaze (P6-P13) and explanations of each instruction and so on. kcpsm6.exe is the compiler for PicoBlaze. The components and its connections of PicoBlaze can be found in user guide page 8.
After downloaded, open zip file and move into Verilog folder. In this folder, kcpsm6.v is the source code for PicoBlaze (also called CDPSM6). ROM_form.v would be used by kcpsm6.exe to generate the memory space. kcpsm6_design_template.v is also helpful even though it is only a template file. This is not a Verilog file that can be simulated or synthesis directly.
STEP 2: Write Assembly Code
The following instructions will light LEDs on Nexys3 with the position in 7, 5, 2, 1, 0. Edit and save them as xxx.psm file.
NOTE: PicoBlaze instruction set can be found in KCPSM6_User_Guide
CONSTANT Acheck, 10100111’b
CONSTANT LED_PORT, 02
Start: LOAD s0, Acheck
OUTPUT s0, LED_PORT
JUMP start
Run kcpsm6.exe to translate .psm into .v (NOTE: ROM_form.vhd will generate VHDL file. If you are using with Verilog, use ROM_form.v in verilog folder).
After compilation, xxx.v will be created. In addition, xxx.log stores detailed information about the assembly code and its corresponding binary code. xxx.hex is the machine code represented in hex.
STEP 3: Create New Project in IDE
Firstly, Open ise(ise_14.7 in this example) and create a new project. Select Spartan-6 FPGA and XC6SLX16, CS324 package. Set Preferred Language to Verilog.
After creating the project, import source files into the project: Right click and select Add Source to import PicoBlaze and memory into the project. Then create a new Verilog file to connect PicoBlaze and memory space and implement other hardware part (e.g. input & output, control 7-seg with hardware).
Copy paste the content in design template file to your top module file (new created file). The design template file includes instantiated PicoBlaze (KCPSM6) and memory space. You will need to change the name of memory space and set .C_FAMILY to S6 and .C_RAM_SIZE_KWORDS to 1 as picture shows below.
The rest of part in design template file gives an example of how to connect PicoBlaze’s input/output and so on. Modify them with your need. In the example, no input but only output is needed and therefore the code can be modified as follows.
STEP 4:Confirm the Correctness of the Design
Create a testbench and generate some input signals to provide in/out signal for top module as following picture shows.
Run simulation tool Isim. Select View as Simulation and start the simulation.
Here is the result. As we can see, output (led) always generate 10100111 which is the same as we expected. 00000000 is due to the fact that it takes time for processor to calculate the output. Each instruction in PicoBlaze takes 2 clock cycle to finish.
STEP 5: Generate Bit File and Download into FPGA Board
Once your design works correctly with simulation, you can generate a programming file and download it into the board.
Select Implementation view and import xxx.ucf file (Nexys3_master.ucf in our example). This file connects your defined port with the port on the board. Modify .ucf file as below picture shows.
Double click Generate Programming File and Synthesis tool will generate .bit file. This may take a while. Connect the board with USB cable and open Adept. Select the .bit and click Program to download the file into Nexys3 board.
After that, you will see LEDs light as you expected.
REF
[1] KCPSM6_User_Guide_30Sept14.pdf
[2] Nexys 3 Reference Manual
[3] https://www.youtube.com/watch?v=7tRkpudwL2g
