The Answer is 42!!: Elbert V2 VHDL Tutorial

It's time for another FPGA tutorial using the Elbert V2 board from Numato Systems!

I found a really good FPGA online course here...so rather than re-invent the wheel I'm going to apply it to the Elbert V2 board.

Hamsterworks FPGA Tutorials

You can download a full PDF of the course from that site if you wish...

I'm going to skip with the module 1 as I have already installed the Xilinx design suite and I'm ready to go. The tutorials are written using VHDL - which I haven't up to now been using however it is similar to verilog so we should be able to manage:

So lets begin at module 2:

I'm referencing this page here if people want to look at the original source material - Kudos to Hamsterworks:

http://hamsterworks.co.nz/mediawiki/index.php/Module_2

The idea of this module is to wire up two switches to two LEDS and have them controlled by an FPGA - in our case the Elbert V2 Development board from Numato Labs. I know we have already done this before but this time we are going to write the source code in VHDL and not in verilog. Hamsterworks' tutorials are very good but are written in VHDL only...so lets get started!!

The first thing to do is to start a new project in Xilinx ISE 14.7 - make sure you choose all of the correct settings as shown in the screenshot below:

Choose a suitable project name and directory etc and click Next when you are ready to continue...

Ensure you also apply all the settings in the screenshot above - especially select VHDL as that is the description language we are going to use...Click Next when you are ready to continue and the summary screen will be displayed:

Click the Finish button and the main Xilinx project screen will be displayed:

Right click in the project area and select add new source file:

Now choose to add a VHDL module - I called mine Switch_LEDS:

Click next to continue:

Now fill in the information for the inputs and outputs. I chose to follow the example by Hamsterworks but there is no reason why we couldn't have 8 switch inputs and 8 LED outputs.

Click Next to Continue and the source code summary page will be displayed:

Click finish to continue and return to the main screen which now looks like the screenshot below:

What we now need to do is edit the source code to our own satisfaction. There are several comments present which can be removed if required - it is entirely at the coder's discretion. We also need to make the code perform the function we want. In our case this means we want the LEDS to mirror the state the switches are in. I changed mine to the following:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity Switch_LEDS is
    Port ( Switch_One : in  STD_LOGIC;
           Switch_Two : in  STD_LOGIC;
           LED_One : out  STD_LOGIC;
           LED_Two : out  STD_LOGIC);
end Switch_LEDS;

architecture Behavioral of Switch_LEDS is

begin

 LED_One <= Switch_One;
 LED_Two <= Switch_Two;

end Behavioral;

So what does this code mean, how does it work etc...

The first line tells the compiler to use the standard library IEEE. The second line tells the compiler to use the IEEE standard representation of a logic value....

The fourth line entity Switch_LEDS is a bit like a setup function in C or C++. It tells the compiler that our design has inputs and outputs (ports) and that there are two inputs known as Switch_One and Switch_Two and also two Outputs known as LED_One and LED_Two.

The 'behaviour' of the function is decided on lines 15 and 16. The '<=' operators in this case mean that the LED_One mirrors the value of Switch_One and the same for LED_Two and Switch_Two

When you are ready save the source code file and click on the 'Green Arrow' on the left side of the screen - Implement top Module:

If the implementation all went according to plan you should be presented with the following in the bottom left corner:

Now we need to tell the compiler where on the Elbert V2 board the switches and LEDS are and which pins they are connected to on the FPGA. To that we need to implement a User Constraints file. Right click in the top right corner of the main project screen and again add a new source file:

This time select Implementation constraints file and give it a suitable file name:

Click Next when you are ready to continue:

Click Finish to continue. We now need to edit the constraints file with the information relating to the Elbert V2 Board. To do that we can look at the file already provided by Numato Labs and / or look at the schematic diagram which shows how the switches and LEDS are connected to the FPGA:

CONFIG VCCAUX = "3.3" ;

NET "MCLK" LOC = P129;
TIMESPEC TS_CLK = PERIOD "CLK" 12 MHz HIGH 50%;


############################################################################
# VGA
############################################################################

    #NET "HSync"              LOC = P93  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "VSync"              LOC = P92 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;

    #NET "Blue[1]"            LOC = P98  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "Blue[0]"            LOC = P96  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;

    #NET "Green[2]"           LOC = P102  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "Green[1]"           LOC = P101  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "Green[0]"           LOC = P99  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;

    #NET "Red[2]"             LOC = P105  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "Red[1]"             LOC = P104  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "Red[0]"             LOC = P103 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;

############################################################################
# Micro SD Card
############################################################################

    #NET "CLK"                LOC = P57  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "DAT0"               LOC = P83  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "DAT1"               LOC = P82  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "DAT2"               LOC = P90  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "DAT3"               LOC = P85  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "CMD"                LOC = P84  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;

############################################################################
# Audio
############################################################################

    #NET "AUDIO_L"            LOC = P88  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "AUDIO_R"            LOC = P87  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ; 

############################################################################
# Seven Segment Display
############################################################################

    #NET "SevenSegment[7]"    LOC = P114  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "SevenSegment[6]"    LOC = P115  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "SevenSegment[5]"    LOC = P116  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "SevenSegment[4]"    LOC = P117  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "SevenSegment[3]"    LOC = P110  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "SevenSegment[2]"    LOC = P111  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "SevenSegment[1]"    LOC = P112  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "SevenSegment[0]"    LOC = P113 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;

    #NET "Enable[3]"          LOC = P124 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "Enable[2]"          LOC = P121 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "Enable[1]"          LOC = P120  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;

############################################################################
# LED
############################################################################

    #NET "LED[8]"            LOC = P46  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "LED[7]"            LOC = P47  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "LED[6]"            LOC = P48  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "LED[5]"            LOC = P49  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "LED[4]"            LOC = P50  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "LED[3]"            LOC = P51  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "LED[2]"            LOC = P54  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "LED[1]"            LOC = P55  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;

############################################################################
# DP Switches
############################################################################

    #NET "DPSwitch[1]"       LOC = P70  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "DPSwitch[2]"       LOC = P69  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "DPSwitch[3]"       LOC = P68  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "DPSwitch[4]"       LOC = P64  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
 #NET "DPSwitch[5]"       LOC = P63  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "DPSwitch[6]"       LOC = P60  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "DPSwitch[7]"       LOC = P59  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "DPSwitch[8]"       LOC = P58  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;

############################################################################
# Switches
############################################################################

    #NET "Switch[1]"         LOC = P80  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "Switch[2]"         LOC = P79  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "Switch[3]"         LOC = P78  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "Switch[4]"         LOC = P77 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "Switch[5]"         LOC = P76 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "Switch[6]"         LOC = P75  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;

############################################################################
# GPIO
############################################################################
 
# HEADER P1

    #NET "gpio_P1[0]"        LOC = P31  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P1[1]"        LOC = P32  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P1[2]"        LOC = P28  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P1[3]"        LOC = P30  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P1[4]"        LOC = P27 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P1[5]"        LOC = P29 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P1[6]"        LOC = P24 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P1[7]"        LOC = P25 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;

# HEADER P6
   
 #NET "gpio_P6[8]"         LOC = P19  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P6[9]"         LOC = P21  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P6[10]"        LOC = P18  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P6[11]"        LOC = P20  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P6[12]"        LOC = P15  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P6[13]"        LOC = P16  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P6[14]"        LOC = P12 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P6[15]"        LOC = P13 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;

# HEADER P2

    #NET "gpio_P2[16]"        LOC = P10  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P2[17]"        LOC = P11  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P2[18]"        LOC = P7  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P2[19]"        LOC = P8  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P2[20]"        LOC = P3  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P2[21]"        LOC = P5  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P2[22]"        LOC = P4  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P2[23]"        LOC = P6  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;

# HEADER P4
    
 #NET "gpio_P4[24]"       LOC = P141  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P4[25]"       LOC = P143  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P4[26]"       LOC = P138  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P4[27]"       LOC = P139  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P4[28]"       LOC = P134  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P4[29]"       LOC = P135  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P4[30]"       LOC = P130 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P4[31]"       LOC = P132 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;


# HEADER P5
    
 #NET "gpio_P5[1]"       LOC = P125  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P5[2]"       LOC = P123  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P5[3]"       LOC = P127  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P5[4]"       LOC = P126  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P5[5]"       LOC = P131  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P5[6]"       LOC = P91  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P5[7]"       LOC = P142 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "gpio_P5[8]"       LOC = P140 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;

All the above code relates to the Elbert V2 board and how the external components are connected to the FPGA device. The schematic diagram on page two shows how the LEDS and switches are electrically connected:

So LED1 and LED2 are connected to pins 55 and 54 and the push button switch 1 and push button switch 2 are connected to pins 80 and 79. If we read through the template user constraints file we can cut and paste the required code from the switches and LEDS sections:

############################################################################
# Switches
############################################################################

    #NET "Switch[1]"         LOC = P80  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "Switch[2]"         LOC = P79  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "Switch[3]"         LOC = P78  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "Switch[4]"         LOC = P77 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "Switch[5]"         LOC = P76 | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    #NET "Switch[6]"         LOC = P75  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;

############################################################################
# LED
############################################################################

    #NET "LED[8]"            LOC = P46  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "LED[7]"            LOC = P47  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "LED[6]"            LOC = P48  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "LED[5]"            LOC = P49  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "LED[4]"            LOC = P50  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "LED[3]"            LOC = P51  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "LED[2]"            LOC = P54  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    #NET "LED[1]"            LOC = P55  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;

We can use this information to generate our own implementation constraints file for this project which will look something similar to:

############################################################################
# Switches
############################################################################

    NET "Switch_One"         LOC = P80  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;
    NET "Switch_Two"         LOC = P79  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST | PULLUP ;

############################################################################
# LED
############################################################################

    NET "LED_Two"            LOC = P54  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;
    NET "LED_One"            LOC = P55  | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = FAST ;

Copy and paste the above code into the text editor window in Xilinx and save the file:

Now it is time to click on the green arrow again to re-compile the project. If all went according to plan the following should be present in the bottom left hand corner of the screen:

Now is the time to generate the Bit stream file. Right click on the Generate programming file option in the bottom left part of the screen, ensure Create Binary Configuration file is checked and click 'run':

If that completes successfully load up the ElbertV2Config program and select the Communications port relating to your Elbert V2 PCB - make sure the board is connected to the PC via a cable and a free USB port - Mine was on COM12:

Then select the open file button and navigate to the folder containing the project we just completed. We need to select the Binary Configuration file and click on the program button:

Once the programming is complete the reset the elbert board and push the buttons! Pressing and holding buttons One and Two should cause the LEDS one and Two to turn off....

For fun reverse this behaviour so that the LEDS are off and pushing and holding the buttons causes then LEDS to illuminate:

It involves changing two of the lines of code with the NOT operator:

 LED_One <= NOT Switch_One;
 LED_Two <= NOT Switch_Two;

Thats all for now....Take care - Langster

The Answer is 42!!

Monday, 24 November 2014

Elbert V2 VHDL Tutorial

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