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Xilinx User Community Forums :
Embedded Solutions :
PicoBlaze :
Re: More basic than "hello world", this bare bones intro project blinks a single LED.
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More basic than "hello world", this bare bones intro project blinks a single LED.
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greglondon
Visitor
Posts: 20
Registered: 11-05-2009
Message 1 of 3
Viewed 157 times
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Here is a bare bones project using the picoblaze. It toggles an LED. It uses a clock in, a reset in (which is optional), and an LED output. Just about every evalutation board has at least a clock and one LED, many have an external pushbutton that can be used as reset. This is a good project for getting the kinks out of your environment, making sure everything is configured properly, confirm that your running the assembler correctly, and confirm that all your hardware is working. It's bare bones enough that you don't need any fancy test equipment, and just about any eval board should be able to run this configuration without adding external hardware or jumpers or whatever. And the LED blinks slowly enough that you don't need an oscilliscope to see the waveform. The assembly code is a simple counter to toggle the LED at a slow enough rate that you can see it with the naked eye. With a 16 Mhz clock, the LED will turn ON about two times a second. if you have a faster clock, you may want to increase the initial value of S2 from 0F to FF. If you have a user-controlled input signal, you can use that as "reset". In this design, reset (active high) will put the picoblaze in reset, but the LED will hold whatever value it last held. If it looks like your LED is always on, it may simply be toggling too fast for your eyes to see it. One way to check is to assert reset a number of times manually. While you push the reset button, the LED should stick to it's last value, on or off. It should be like a coin toss, about half and half. If you hit reset a bunch of times but the LED always stays on, then something isn't working. If you hit reset a bunch of times and the LED is a coin toss between on and off, then increase your S2 initial value or decrease your clock frequency. If you don't have a reset signal that you can control, just tie the signal to zero. module picoblaze_toggle( input FPGA_RESET, input CLK_16MHZ, output LED1 ); wire clock = CLK_16MHZ; // reset is active high. // if no reset signal input // then tie reset to zero here. wire reset = FPGA_RESET; wire [7:0] port_id; wire write_strobe; wire read_strobe; wire [7:0] out_port; wire [7:0] in_port=0; wire interrupt=0; wire interrupt_ack; embedded_kcpsm3 EMBEDDED( .port_id(port_id), .write_strobe(write_strobe), .read_strobe(read_strobe), .out_port(out_port), .in_port(in_port), .interrupt(interrupt), .interrupt_ack(interrupt_ack), .reset(reset), .clk(clock) ); // only one bit written to by picoblaze, the LED. // therefore don't need to decode port_id. // if write_strobe asserts, grab out_port[0] and // hold it in userbit. reg userbit = 0; always @(posedge clock) begin if(write_strobe) begin userbit <= out_port[0]; end end assign LED1 = userbit; endmodule This is the assembly for the toggle project. All the code does is count a really long time and then invert the LED. The total count is controlled by the initial values of s0, s1, s2. with a 16 mhz clock, this code ends up toggling the LED on 2 times a second. Increase S2 initial value from 0F to FF to slow the LED down even further. start: LOAD s9, 00 drive_wave: OUTPUT s9, 02 ; write s9 register to userbit LOAD S2, 0F ; S2 initial valueloop2: LOAD S1, FF ; S1 initial valueloop1: LOAD s0, FF ; S0 initial valueloop0: SUB s0, 01 JUMP NZ, loop0 SUB s1, 01 JUMP NZ, loop1 SUB s2, 01 JUMP NZ, loop2 ; XOR s9, FF ;toggle register JUMP drive_wave
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Solved!
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11-06-2009 08:13 PM
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Re: More basic than "hello world", this bare bones intro project blinks a single LED.
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greglondon
Visitor
Posts: 20
Registered: 11-05-2009
Message 2 of 3
Viewed 156 times
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See if I can get the carriage returns right this time: Here's the verilog: module picoblaze_toggle( input FPGA_RESET, input CLK_16MHZ, output LED1 ); wire clock = CLK_16MHZ; // reset is active high. // if no reset signal input // then tie reset to zero here. wire reset = FPGA_RESET; wire [7:0] port_id; wire write_strobe; wire read_strobe; wire [7:0] out_port; wire [7:0] in_port=0; wire interrupt=0; wire interrupt_ack; embedded_kcpsm3 EMBEDDED( .port_id(port_id), .write_strobe(write_strobe), .read_strobe(read_strobe), .out_port(out_port), .in_port(in_port), .interrupt(interrupt), .interrupt_ack(interrupt_ack), .reset(reset), .clk(clock) ); // only one bit written to by picoblaze, the LED. // therefore don't need to decode port_id. // if write_strobe asserts, grab out_port[0] and // hold it in userbit. reg userbit = 0; always @(posedge clock) begin if(write_strobe) begin userbit <= out_port[0]; end end assign LED1 = userbit; endmodule Here's teh assembly code: start: LOAD s9, 00 drive_wave: OUTPUT s9, 02 ; write s9 register to userbit LOAD S2, 0F ; S2 initial value loop2: LOAD S1, FF ; S1 initial value loop1: LOAD s0, FF ; S0 initial value loop0: SUB s0, 01 JUMP NZ, loop0 SUB s1, 01 JUMP NZ, loop1 SUB s2, 01 JUMP NZ, loop2 ; XOR s9, FF ;toggle register JUMP drive_wave
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 Accepted Solution
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11-06-2009 08:16 PM
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Re: More basic than "hello world", this bare bones intro project blinks a single LED.
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 kcmman
Xilinx Employee
Posts: 138
Registered: 09-05-2007
Message 3 of 3
Viewed 102 times
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Thank you for this; I am a great believer that there is no such thing as an example that is too simple. Regards,
Ken Chapman
Senior Staff Engineer, Applications Specialist, Xilinx UK
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11-10-2009 01:16 AM
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