these is a problem for me,i need some help.
how can i use verilog describe 2^n -1 the input interface is input[3:0] n; the output interface is output [15:0] result; i know can use a table ,but these is some other describe thanks链接已复制
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if it is just that simple you could write
module MyPower ( clk , In_N , Out_P ); input clk; input [ 3:0] In_N; output [15:0] Out_P; reg [15:0] Out_P; always @ ( posedge clk ) case ( In_N ) 4'd0 : Out_P <= 16'd1; 4'd1 : Out_P <= 16'd2; 4'd2 : Out_P <= 16'd4; 4'd3 : Out_P <= 16'd8; 4'd4 : Out_P <= 16'd16; 4'd5 : Out_P <= 16'd32; 4'd6 : Out_P <= 16'd64; 4'd7 : Out_P <= 16'd128; 4'd8 : Out_P <= 16'd256; 4'd9 : Out_P <= 16'd512; 4'd10 : Out_P <= 16'd1024; 4'd11 : Out_P <= 16'd2048; 4'd12 : Out_P <= 16'd4096; 4'd13 : Out_P <= 16'd8192; 4'd14 : Out_P <= 16'd16384; 4'd15 : Out_P <= 16'd32768; endcase endmodule but you could try to implement some kind of shift functionalityIf I understood the question (4 to 16 decoder) then MSchmitt's coding is how I would implement this as well. If you don't want the decoder registered then you would write it like this:
reg [15:0] Out_P; always @ (In_N) begin case (In_N) 4'd0 : Out_P = 16'd1; 4'd1 : Out_P = 16'd2; 4'd2 : Out_P = 16'd4; 4'd3 : Out_P = 16'd8; 4'd4 : Out_P = 16'd16; 4'd5 : Out_P = 16'd32; 4'd6 : Out_P = 16'd64; 4'd7 : Out_P = 16'd128; 4'd8 : Out_P = 16'd256; 4'd9 : Out_P = 16'd512; 4'd10 : Out_P = 16'd1024; 4'd11 : Out_P = 16'd2048; 4'd12 : Out_P = 16'd4096; 4'd13 : Out_P = 16'd8192; 4'd14 : Out_P = 16'd16384; 4'd15 : Out_P = 16'd32768; endcase endFirst could you clarify? Are you trying to get:
a) (2^n)-1 or b) 2^(n-1) I suspect it's a). If not let me know.
module pow_2toN(
input n,
output result
);
wire shift_reg;
assign shift_reg = {16'd0,16'hffff} << n;
assign result = shift_reg;
endmodule or... module pow_2toN(
input n,
output result
);
genvar i;
generate
for(i=0;i<16;i=i+1) begin : result_assigns
assign result = (i < n) : 1'b1 : 1'b0;
end
endgenerate
endmodule
or... module pow_2toN(
input n,
output reg result
);
integer i;
always @* begin
result = 16'd0;
for(i=0;i<16;i=i+1)
if(i<n) result = 1'b1;
end
endmodule
or... module pow_2toN(
input n,
output reg result
);
integer i;
always @* begin
result = 16'd1;
for(i=1;i<16;i=i+1)
if(i<=n) result = {result,1'b0};
result = result + 16'hffff;
end
endmodule
We could keep going but I digress. I may have some typos in there. What might be entertaining for you is to try all these variants and see what wildly different compilation results they produce. Jake
Oh Jake great , thats real fun to read and think about.
first example should be assign shift_reg = {16'd1,16'h0000} << n; to get the 1,2,4,8,... instead of 0,1,3,7,f,1f,... It's realy a lesson worth to go through them all and understand them ...--- Quote Start --- If I understood the question (4 to 16 decoder) then MSchmitt's coding is how I would implement this as well. If you don't want the decoder registered then you would write it like this: reg [15:0] Out_P; always @ (In_N) begin case (In_N) 4'd0 : Out_P = 16'd1; 4'd1 : Out_P = 16'd2; 4'd2 : Out_P = 16'd4; 4'd3 : Out_P = 16'd8; 4'd4 : Out_P = 16'd16; 4'd5 : Out_P = 16'd32; 4'd6 : Out_P = 16'd64; 4'd7 : Out_P = 16'd128; 4'd8 : Out_P = 16'd256; 4'd9 : Out_P = 16'd512; 4'd10 : Out_P = 16'd1024; 4'd11 : Out_P = 16'd2048; 4'd12 : Out_P = 16'd4096; 4'd13 : Out_P = 16'd8192; 4'd14 : Out_P = 16'd16384; 4'd15 : Out_P = 16'd32768; endcase end --- Quote End --- this is also a ROM can it describe wtih register?
--- Quote Start --- First could you clarify? Are you trying to get: a) (2^n)-1 or b) 2^(n-1) I suspect it's a). If not let me know.
module pow_2toN(
input n,
output result
);
wire shift_reg;
assign shift_reg = {16'd0,16'hffff} << n;
assign result = shift_reg;
endmodule or... module pow_2toN(
input n,
output result
);
genvar i;
generate
for(i=0;i<16;i=i+1) begin : result_assigns
assign result = (i < n) : 1'b1 : 1'b0;
end
endgenerate
endmodule
or... module pow_2toN(
input n,
output reg result
);
integer i;
always @* begin
result = 16'd0;
for(i=0;i<16;i=i+1)
if(i<n) result = 1'b1;
end
endmodule
or... module pow_2toN(
input n,
output reg result
);
integer i;
always @* begin
result = 16'd1;
for(i=1;i<16;i=i+1)
if(i<=n) result = {result,1'b0};
result = result + 16'hffff;
end
endmodule
We could keep going but I digress. I may have some typos in there. What might be entertaining for you is to try all these variants and see what wildly different compilation results they produce. Jake --- Quote End --- Hi jakobjones I am sorry it is (a) assign shift_reg = {16'd0,16'hffff} << n; Is this a RTL description?
--- Quote Start --- this is also a ROM can it describe wtih register? --- Quote End --- What I wrote wouldn't be synthesized as a ROM (in an Altera FPGA) since it's not synchronous. Instead you'll get the same muxing logic only the result isn't registered. Here is a good doc to take a look at to learn more about HDL coding styles and how they map to the FPGA logic: http://www.altera.com/literature/hb/qts/qts_qii51007.pdf The short forms using the shift operation I suspect will synthesize into the same multiplexer structure from the case statement. A variable shift operation (barrelshift) is a multiplexer of the same data under different shift distances. The shift amount maps to the select bits of the mux. Like others have said try various codings and see if any give better results. It's easier to try various things and let synthesis do all the heavy lifting instead of the other way around :)
I don't assume significant differences in the synthesis results. The expression for each output signal should fit a 4-input -LUT, so it can be expected, that all logical equivalent descriptions end up in the same circuit.
--- Quote Start --- What I wrote wouldn't be synthesized as a ROM (in an Altera FPGA) since it's not synchronous. Instead you'll get the same muxing logic only the result isn't registered. Here is a good doc to take a look at to learn more about HDL coding styles and how they map to the FPGA logic: http://www.altera.com/literature/hb/qts/qts_qii51007.pdf The short forms using the shift operation I suspect will synthesize into the same multiplexer structure from the case statement. A variable shift operation (barrelshift) is a multiplexer of the same data under different shift distances. The shift amount maps to the select bits of the mux. Like others have said try various codings and see if any give better results. It's easier to try various things and let synthesis do all the heavy lifting instead of the other way around :) --- Quote End --- BadOmenthank you very much . As you said,it will synthesize into the same multiplexer structure from the case statement so if i interface a ROM it can save so much resource ?
That is correct, you can use a small ROM as a lookup table based decoder. Just follow the ROM coding style in that link I posted. Keep in mind that this ROM will have a latency of one clock cycle.
