Simple blinking LED

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This design introduce FPGA usage on APF. The design will allow you to synthesize a design and configure the FGPA to blink a LED.

The design

VHDL code

The VHDL code above describe a clock divider by 48000000 to generate a 0.5 Hz clock that will blink the LED.

 library IEEE;
 use IEEE.numeric_std.all;
 entity led is
    Port ( 
           refclk : in  std_logic;
           led : out std_logic
 end led;
 architecture RTL of led is
    constant max_count : natural := 48000000;
    signal Rst : std_logic;

    Rst <= '0';
    -- 0 to max_count counter
    compteur : process(refclk, Rst)
        variable count : natural range 0 to max_count;
        if Rst = '1' then
            count := 0;
            led <= '1';
        elsif rising_edge(refclk) then
            if count < max_count/2 then
                count := count + 1;
                led <= '1';
            elsif count < max_count then
                led <= '0';
                count := count + 1;
                led <= '1';
                count := 0;
            end if;
        end if;
    end process compteur; 
 end RTL;


To synthesize this code, use Xilinx Web Pack, create a new project and add this VHDL module.

Note Note: Don't forget to power the FPGA IO bank as explained in datasheet

ISE/Quartus need to know where to branch LED pins on its IO, this pinout is describe in constraint file with extension .ucf.

  • For APF9328:
# Clock at 96MHz
NET "Clk" LOC = "P55";
NET "Clk" TNM_NET = "Clk";
TIMESPEC "TS_Clk" = PERIOD "Clk" 10.42 ns HIGH 50 %;
NET "led" LOC = "P118"| IOSTANDARD = LVCMOS33 ;
  • For APF27
# Clock at 100MHz
NET "Clk" LOC = "N9"; # CLK0
NET "Clk" TNM_NET = "Clk";
TIMESPEC "TS_Clk" = PERIOD "Clk" 10 ns HIGH 50 %;
NET "led" LOC = "C15"| IOSTANDARD = LVCMOS33 ; #IO_L24N_1
  • For APF51
# Clock at 92.85MHz
NET "Clk" LOC = "N8"; # EIM_BCLK
NET "Clk" TNM_NET = "Clk";
TIMESPEC "TS_Clk" = PERIOD "Clk" 10.77 ns HIGH 50 %;
  • For APF6_SP
# Clock is the differential PCIe clock (LVDS) at 100MHz
set_instance_assignment -name IO_STANDARD "1.5-V PCML" -to Clk
set_location_assignment PIN_V4 -to Clk
set_location_assignment PIN_U4 -to "Clk(n)"
# For the first apf6dev serie this pin must be used :
set_location_assignment PIN_M10 -to led 
# Others apf6dev will use PIN_K15

These constraints files examples can be found in Armadeus BSP's firmware/leds/blinking_led/src/ directory.

Generate bitstream


Once these two files are written, FPGA configuration file, also named "bitstream", can be generated by clicking on Synthetize - XST then Implement Design and finally Generate Programming File. If all these operations are correctly done, a file with ".bit" extension will be generated.


See the Quartus page for tutorials.

Configure FPGA

To configure FGPA the bitstream must be downloaded from Host to APF's memory and then from APF's memory to FPGA.

Host to APF

Downloading Bitstream from Host to APF can be done in different way : with tftp from U-Boot, with tftp from Linux, with serial from U-Boot or with nfs from Linux. Here the file is downloaded with tftp in U-Boot:

  • First copy bitstream in the host tftp directory:
 cp blinking_led_apfXX_200k.bit /tftpboot
  • Then download it in APF ram with U-Boot command :
 BIOS> tftpboot ${loadaddr} blinking_led_apfXX_200k.bit
 dm9000 i/o: 0x15c00000, id: 0x90000a46 
 MAC: 00:0e:32:00:00:01
 operating at 10M half duplex mode
 TFTP from server; our IP address is
 Filename 'Clk_div_led.bit'.
 Load address: 0x8000000
 Loading: T ##########################
 Bytes transferred = 131029 (1ffd5 hex)


Finally, to download bitstream in FPGA (to configure the FGPA) use the U-Boot fpga command:

 BIOS>fpga load 0 ${loadaddr} ${firmware_len}

FPGA configuration can also be done in Linux.

Enjoy the beauty of a blinking LED

To see the LED blinking, the FPGA bank must be powered as explain in the datasheet.