FPGA Programming with Linux
In order to show you what it's like to design custom digital hardware and how FPGA development software works, I've modified one of the demo circuits loaded into the Starter Kit, the DNA reader by Xilinx Senior Engineer Ken Chapman.
Spartan FPGAs have a unique ID number, called DNA. The DNA reader displays the intro string “DNA Reader by Ken Chapman”, and then this number is displayed on the LCD screen (Figure 5), working as shown in Figure 6. An Xilinx hardware macro called dna_port reads the DNA ID from the silicon. A PicoBlaze processor first displays the intro string, then gets the DNA ID from dna_port and finally sends it, one character at a time, to the LCD interface through the lcd_d data bus. The PicoBlaze code is stored into the dna_ctrl ROM.
My modification consists of a small extra circuit that overwrites the default intro string on the fly with one saying “M Fioretti Linux Journal”. Be warned that this is a hack made only for demo purposes. In the real world, if you actually needed to change that string, it would make much more sense to rewrite the PicoBlaze assembly code. Because this is an article about HDL design in FPGAs, however, I went for a solution based on easy-to-read HDL code whose effect is easily visible in one picture.
My extra circuit is shown in red in Figure 6: a counter and decoder that detect when the PicoBlaze is driving the LCD data port (lcd_d) and send different characters to it. The VHDL source code corresponding to this extra hardware is shown in Listing 1, which is not the complete, working VHDL file I used, but only an excerpt meant to give you an idea of how HDL coding works.
Lines 1–12 define input and output ports of the top-level circuit, the reading_dna module. You must declare all internal registers and wires before using them (lines 17–23). HDLs support hierarchy; you can instantiate other modules by declaring them and connecting all their ports to the right signals (lines 26–49). Line 53 shows a first example of a synchronous process. Depending on the value of the cnt_ops counter, whenever there is a positive edge of the clock (line 56) and the processor sets the signals write_strobe and port_id(6) high, the lcd_output_data register loads the character from the processor or the one from my extra logic (lines 62–68). The cnt_and_new_chars process starting at line 80 does the real work. First, it samples the LCD enable signal to count (line 91) the write accesses to the LCD. One cycle after a write occurs, working with the new counter value (line 99), the process calculates the next current_character that should be displayed. If you look at lines 101–125 you'll see that, instead of the DNA number, the display should show the ASCII string “M Fioretti Linux Journal”. A quick simulation (Figure 7) proves that the new process sends those characters to the display at the right times—that is, when the lcd_rs signal is high (low would indicate LCD configuration commands).
Listing 1. VHDL Source Code
1 entity reading_dna is 2 Port ( led : out std_logic_vector(7 downto 0); 3 lcd_d : inout std_logic_vector(7 downto 0); 4 lcd_rs : out std_logic; 5 lcd_rw : out std_logic; 6 lcd_e : out std_logic; 7 j2_30 : out std_logic; 8 j2_26 : out std_logic; 9 j2_22 : out std_logic; 10 j2_14 : out std_logic; 11 clk : in std_logic); 12 end reading_dna; 13 -- 14 architecture Behavioral of reading_dna is 15 -- 16 17 -- start extra signals for LJ demo 18 signal lcd_e_copy : std_logic; 19 signal lcd_e_del_1 : std_logic; 20 signal lcd_e_del_2 : std_logic; 21 signal current_character : std_logic_vector(7 downto 0); 22 signal cnt_ops : integer range 0 to 49999999 := 0; 23 -- end extra signals for LJ demo 24 begin 25 26 device_dna: dna_port 27 port map( din => dna_din, 28 read => dna_read, 29 shift => dna_shift, 30 dout => dna_dout, 31 clk => dna_clk); 32 33 processor: kcpsm3 34 port map( address => address, 35 instruction => instruction, 36 port_id => port_id, 37 write_strobe => write_strobe, 38 out_port => out_port, 39 read_strobe => read_strobe, 40 in_port => in_port, 41 interrupt => interrupt, 42 interrupt_ack => interrupt_ack, 43 reset => kcpsm3_reset, 44 clk => clk); 45 46 program_rom: dna_ctrl 47 port map( address => address, 48 instruction => instruction, 49 clk => clk); 50 51 kcpsm3_reset <= '0'; 52 53 output_ports: process(clk) 54 begin 55 56 if clk'event and clk='1' then 57 if write_strobe='1' then 58 59 -- 8-bit LCD data output address 40 hex. 60 61 if port_id(6)='1' then 62 -- lcd_output_data <= out_port; 63 --extra code for LJ demo 64 if ((cnt_ops >= 8 and cnt_ops <= 17) or 65 (cnt_ops >= 19 and cnt_ops <= 32)) then 66 lcd_output_data <= current_character; 67 else 68 lcd_output_data <= out_port; 69 end if; --end extra code for LJ demo 70 end if; 71 72 end if; 73 74 end if; 75 76 end process output_ports; 77 78 -- LCD interface 79 80 cnt_and_new_chars: process(clk) 81 begin 82 if clk'event and clk='1' then 83 84 if port_id(5)='1' and write_strobe='1' then 85 lcd_e_copy <= out_port(0); 86 end if; 87 88 lcd_e_del_1 <= lcd_e_copy; 89 lcd_e_del_2 <= lcd_e_del_1; 90 91 if (lcd_e_copy ='1' and lcd_e_del_1='0') then -- posedge 92 if cnt_ops=49999999 then -- inc counter 93 cnt_ops <= 0; 94 else 95 cnt_ops <= cnt_ops + 1; 96 end if; -- if cnt_ops=49999999 97 end if; -- end (lcd_e_copy ='1' and lcd_e_del_1='0') 98 99 if (lcd_e_del_1 ='1' and lcd_e_del_2='0') then -- posedge 100 case cnt_ops is -- character generator 101 when 8 => current_character <= "01001101"; -- M 102 when 9 => current_character <= "00100000"; -- space 103 when 10 => current_character <= "01000110"; -- F 104 when 11 => current_character <= "01101001"; -- i 105 when 12 => current_character <= "01101111"; -- o 106 when 13 => current_character <= "01110010"; -- r 107 when 14 => current_character <= "01100101"; -- e 108 when 15 => current_character <= "01110100"; -- t 109 when 16 => current_character <= "01110100"; -- t 110 when 17 => current_character <= "01101001"; -- i 111 112 when 19 => current_character <= "01001100"; -- L 113 when 20 => current_character <= "01101001"; -- i 114 when 21 => current_character <= "01101110"; -- n 115 when 22 => current_character <= "01110101"; -- u 116 when 23 => current_character <= "01111000"; -- x 117 when 24 => current_character <= "00100000"; -- space 118 when 25 => current_character <= "01001010"; -- J 119 when 26 => current_character <= "01101111"; -- o 120 when 27 => current_character <= "01110101"; -- u 121 when 28 => current_character <= "01110010"; -- r 122 when 29 => current_character <= "01101110"; -- n 123 when 30 => current_character <= "01100001"; -- a 124 when 31 => current_character <= "01101100"; -- l 125 when 32 => current_character <= "00100000"; -- space 126 127 when others => current_character <= "00100000"; -- space 128 129 end case; 130 end if; -- end (lcd_e_del_1 ='1' and lcd_e_del_2='0') 131 132 133 end if; -- clk'event and clk='1' 134 end process cnt_and_new_chars;
The procedure to transform this really simple HDL model into properly connected gates on silicon is equally simple. Double-click, one at a time, the icons in the left-center pane of the Project Navigator shown in Figure 1: synthesize, Implement Design, Generate Programming File and Configure Target Device. If you clicked directly on the last one, ISE would do all the previous steps in the right order anyway, but doing it in steps is a better way to learn. Eventually, you'll get the bit file and a final report like the one shown in Figure 8, showing how much silicon was used. Remember, what we just did is actual hardware—that is, transistors directly connected to do, in real time, what we ordered them to do. All that remains to make it actually happen is to load the bit file in the FPGA. Figure 9 shows the result.
Articles about Digital Rights and more at http://stop.zona-m.net CV, talks and bio at http://mfioretti.com
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
Free to Linux Journal readers.Register Now!
- SourceClear Open
- SUSE LLC's SUSE Manager
- Tech Tip: Really Simple HTTP Server with Python
- Linux in Government: Open Source Innovation within the DoD
- Managing Linux Using Puppet
- LAMP Development at Public Sector Web Sites
- Returning Values from Bash Functions
- July 2016 Issue of Linux Journal
- My +1 Sword of Productivity
- Linux Access in State and Local Government, Part VII
With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide